Final report for LNE14-333
Project Information
Replacement ewe lambs can comprise 30% of the breeding flock and are the vehicle for genetic improvement of the flock and the means through which the size of the flock is maintained or expanded. Therefore, the fertility and productivity of replacement ewe lambs has a major impact on the overall productivity and profitability of the flock. Most reports indicate the productivity of ewe lambs is substantially lower than that of adult ewes. Lambing rates (lambs born per ewe exposed) of ewe lambs as low as 27-38% have been previously reported compared to in excess of 125% in adult ewes. Our recent studies indicate that replacement females produce 35 less lambs per 100 females than adult ewes. In WV where ~5000 replacements are bred annually this translates into a reduction in revenue of between $350,000-425,000/year. Additionally, mortality rates are higher and growth rate is slower in lambs born to ewe lambs, and ewe lambs that fail to lamb receive a significantly discounted price when sold at an older age as culled yearlings. Delaying breeding to the second breeding season when females are 18-20 months old decreases profitability due to the higher cost involved, and, a lower lifetime productivity compared to females bred to lamb as yearlings. The fertility of replacement ewe lambs can be improved by nutritional manipulation to ensure females are bred for the first time at heavier weights through selection adjusting the month of breeding and by reproductive management techniques including treatment with progesterone containing CIDR devices. In a survey of 100 producers all 60 respondents, reported lower performance of their replacement ewe lambs and considered it a serious problem. However, despite the potential ability of selection, nutritional and reproductive management strategies to enhance the productivity and profitability of replacement females, few producers (8/60) employed management practices to address the problem and none (0/60) was able to quantify the economic impact of lower reproductive performance in replacement females. Further, despite the potential negative impact on lifetime productivity of the female and associated losses, most respondents (46/60) delayed breeding replacement females for the first time until 15-20 months. Our preliminary studies show a 20-30% lower lambing rate in older replacement females, similar to that of ewe lambs. Sixty six percent of producers indicated interest in learning about practices to improve reproductive performance, and increase profits associated with rearing ewe lambs.
At the end of the first full-year of our studies, we demonstrated that increasing the plane of nutrition and the use of progesterone pretreatment can increase lambing rates and in so doing increase profitability for producers. We also demonstrated that the age at first breeding can be reduced to 9 months without negatively impacting fertility and in so doing reduce the cost of raising replacement females.
Further, we showed that progesterone pretreatment and gonadotropin stimulation can be used to successfully breed fall-born ewe lambs during the anestrous period, facilitating the implementation of out-of-season breeding programs and higher prices for lambs born from such breeding programs. The use of anti-Mullerian hormone (AMH) as a marker of fertility in replacement females is currently being examined. Findings of our studies have been presented to approximately 75 producers in Pennsylvania and West Virginia.
Introduction:
Replacement ewe lambs can comprise 30% of the breeding flock and are the vehicle for genetic improvement of the flock and the means through which the size of the flock is maintained or expanded. Therefore, the fertility and productivity of replacement ewe lambs has a major impact on the overall productivity and profitability of the flock. Most reports (12) indicate the productivity of ewe lambs is substantially lower than that of adult ewes. Lambing rates (lambs born per ewe exposed) of ewe lambs as low as 27-38% have been previously reported (12) compared in excess of 125% in adult ewes. Our recent studies indicate that replacement females produce 35 less lambs per 100 females than adult ewes. In WV where ~5000 replacements are bred annually this translates into a reduction in revenue of between $35,000-425,000/year. Additionally, mortality rates are higher and growth rate is slower in lambs born to ewe lambs (1), and ewe lambs that fail to lamb receive a significantly discounted price when sold at an older age as culled yearlings. Delaying breeding to the second breeding season when females are 18-20 months old decreases profitability due to the higher cos involved, and, a lower lifetime productivity compared to females bred to lamb as yearlings (6). The fertility of replacement ewe lambs can be improved by nutritional manipulation to ensure females are bred for the first time at heavier weights (3,5,11), through selection (11), adjusting the month of breeding and by reproductive management techniques (15) including treatment with progesterone containing CIDR devices. In a survey of 100 producers all 60 respondents reported lower performance of their replacement ewe lambs and considered it a serious problem. However, despite the potential ability of selection, nutritional and reproductive management strategies to enhanced the productivity and profitability of replacement females, few producers (8/60) employed management practices to address the problem and none (0/60) was able to quantify the economic impact of lower reproductive performance in replacement females. Further, despite the potential negative impact on lifetime productivity of the female and associated losses, most respondents (46/60) delayed breeding replacement females for the first time until 15-20 months. Our preliminary studies show a 20-30% lower lambing rate in older replacement females, similar to that of ewe lambs. Sixty-six percent of producers indicated interest in learning about practices to improve reproductive performance, and increase profits associated with rearing ewe lambs.
This project engages sheep producers in WV, PA and MD in an education program on management practices that enhance productivity of ewe lambs, including reproductive management, selection, health and disease, nutritional, and economic and financial benefits of improved productivity of replacement ewe lambs. The in-farm research trials investigate the use of newer reproductive technologies and strategic feeding on performance and profitability of replacement ewe lambs.
The management of replacement ewe lambs has been chosen as the focus of this research project because of the low level of productivity, resulting in significant loss of revenue and lower profitability of sheep operations, and due to the low rate of adoption of selection, nutritional and reproductive management strategies and technologies are capable of increasing the lambing rate of replacement females. The different management strategies have the potential for additive effects on replacement female productivity, therefore, they can be collectively or independently adopted by a wide cross section of sheep producers including “green” producers. Replacement females derived from dams with high reproductive performance, those with genetic potential for rapid post weening gains have a higher probability of becoming pregnant in the first year of life, and therefore, improving selection can ensure females with the highest probability of becoming pregnant are retained. Irrespective of age, females that are heavier at the beginning of the breeding season have a higher probability of becoming pregnant retaining pregnancy and having multiple births, therefore, nutritional management strategies will increase lambing rates of replacement females by ensuring optimal body weights and body condition are attained at the start of the breeding season. Pre-treatment with progestogens increase the total number of females becoming pregnant early and throughout the breeding season. Pre-treatment with CIDRS, which contains the natural hormone, progesterone is now available to sheep producers in the USA and can increase the proportion of females becoming pregnant early in the breeding season. Ultrasonographic pregnancy diagnosis allows the early detection of non-pregnant females, females culled early in life can be sold as market lambs without significant price discounts and without incurring significant additional feeding cost. The management strategies employed will increase the productivity of replacement lambs by 20-50%, thereby enhancing revenue generated by $70-85 per replacement female in the breeding flock, while simultaneously reducing losses associated with maintain non-productive females.
The objective of the research component of the project is to assess and demonstrate the efficacy of various replacement ewe lamb management strategies. We will use ewe lambs that are 7-15 months at breeding to test the following hypotheses: 1. the fertility and prolificacy increases with weight at breeding independent of age 2. Fertility of ewe lambs increases with progesterone pretreatment independent of age 3. Fertility in ewe lambs is positively correlated with serum concentrations of AMH. The project also includes a comprehensive educational program and on-farm trials on approaches to enhance the productivity of ewe lambs.
On conclusion we project that 60 sheep producers will adopt reproductive and other management practices (selection, nutrition) to enhance productivity of 3000 ewe lambs costing an additional of $8-10 per animal treated, and will increase lambing rate by 30-40%, producing 900 more lambs valued at ~$220,000 each year.
Cooperators
Research
The objective of the research component is to assess and demonstrate the efficacy of various replacement ewe lamb management strategies. We will use ewe lambs that are 7-15 months at breeding to test the following hypotheses: 1. the fertility and prolificacy increases with weight at breeding independent of age 2. Fertility of ewe lambs increases with progesterone pre-treatment independent of age 3. Fertility in ewe lambs is positively correlated with serum concentrations of anti-mullerian hormone.
Experiment 1:
The procedures used in these studies were approved by the West Virginia University Animal Care and Use Committee (ACUC # 13-1101). All animals were older than the age normally associated with attainment of puberty for the breed/type and possessed a BCS of ≥3. Three studies were conducted to evaluate the effect of progesterone pre-treatment and gonadotropic stimulation on the reproductive performance of nulliparous females. The first study utilized ewe lambs of mixed breeding (N = 191) born in mid-October through mid-December of 2010 and 2011 and was conducted during the mid-anestrous period (May to early July) of 2011 and 2012 on five farms located in West Virginia and south-western Pennsylvania. The second and third studies were conducted beginning in May (study 2) and late August (study 3) at a farm located in southwestern Pennsylvania. The animals used in these studies consisted of spring-born Dorset X Texel yearlings (N = 120, 15-months-old and N = 104, 17-months-old for studies 2 and 3, respectively). In the third study a single blood sample was collected via jugular venipuncture and assayed for progesterone as described by Sheffel et al. (1982). The limit of detection was 0.1 ng/mL, and the intra and interassay coefficients of variation were 7.1 and 18%, respectively. Animals with concentrations of progesterone >1 ng/mL (N = 11) were considered to be ovulatory and were removed from the study. Animals were not previously exposed to rams and were managed on mixed grass:legume pastures with ad libitum access to water and shade.
To evaluate the effect of gonadotropic stimulation on fertility of fall-born ewe lambs and yearlings during the mid-anestrous period (May through July), a controlled internal drug releasing (CIDR) device (containing 0.3 g of progesterone; Pfizer Animal Health, New York, NY, now Zoetis Animal health, Kalamazoo, MI) was applied to each ewe for 5 days prior to ram introduction. At CIDR removal, ewes were assigned randomly to receive either gonadotropic stimulation with an injection of the gonadotropin mixture [3 mL P.G. 600®, i.m. (240 IU eCG, 120 IU hCG), Intervet, Millsboro, DE; CIDRPG] or no further treatment (CIDR) and were joined with a group of sexually mature rams at a ratio not less than 1 ram per 18 nulliparous ewes. To evaluate the effect of gonadotropic stimulation on yearling nulliparous ewes during late anestrous or early breeding season were treated similar to the first 2 studies, but also included a group of ewes that did not receive either progesterone or gonadotropic stimulation (Control).
Experiment 2:
The procedures used in these studies were approved by the West Virginia University Animal Care and Use Committee (IACUC # 13-1201). This experiment was conducted during the fall of 2013, 2014 and 2015 on three farms located in West Virginia and southwestern Pennsylvania. The animals used in this study consisted of Dorset x Texel (8.7 ± 0.1 months [range 4 – 10.4 months]; 38.9 ± 0.58 kg [range 23.1- 70.3 kg]), Katahdin (6.9 ± 0.04 months [range 3.6 – 5.6 months]; 23.6 ± 0.57 kg [range 13.1 – 35.8 kg]), and Suffolk (40.5 ± 0.75 kg [range 28.2 – 53.1 kg]) replacement females. Two months prior to beginning of the breeding season, replacement females were provided with a grain supplement (15% crude protein, 65% total digestible nutrients concentrate) ranging in amounts of 0.23 to 0.68 kg per head per day. All animals were managed on mixed grass legume pastures and were allowed ad libitum access to water and shade.
Study 1: To determine the effect of breed of sheep on the concentration of AMH, a single blood sample was collected from Dorset/Texel (n = 238), Suffolk (n = 44) and Katahdin (n = 77) replacement females (Table 4) and assayed for AMH. To determine the relationship between age and concentration of AMH, blood samples were collected from Dorset/Texel and Katahdin replacement females ranging in age from 6 to 12 and 6 to 8 months, respectively.
Study 2: To determine the relationship between the concentration of AMH and fertility, the concentration of AMH was determined from a single blood sample collected 2 months prior to breeding. Females within the Katahdin breed and Dorset/Texel crosses, were placed into LOW, MEDIUM and HIGH groups respectively, equivalent to < mean - ½ standard deviation, ≥ mean - ½ standard deviation < mean + ½ standard deviation and ≥ mean + ½ standard deviation, respectively. Females within the Suffolk breed was not used as the producer experienced significant loss of animals due to sickness. All females were separated from rams prior to the beginning of the experiment and received progesterone via a CIDR device (containing 0.3g of progesterone; InterAg; Hamilton, New Zealand) for 5 days prior to ram introduction. At CIDR removal, replacement females were exposed to a group of sexually mature rams at a ratio not less than one ram per 15 replacement females.
TREATMENTS
Ewe lambs 7-13 months old would be randomly assigned to receive either a high or low plane of nutrition with or without progesterone pre-treatment. Treatment 1: Main effect nutrition level: Two months prior to beginning of the breeding season ewe lambs would either be assigned to a low plane (LP) of nutrition –free access to average quality forage, 10% CP, 55%TDN or high plane (HP) of nutrition by providing 1.5lbs supplement of a 15% CP, 65% TDN concentrate and free access to forage. Significant evidence exist that heavier weight at breeding is associated with increase pregnancy rates, lower embryonic mortality and higher prolificacy irrespective of age, thereby, providing a non-pharmaceutical approach to increase performance of replacement ewe lambs. Treatment 2: Main effect progesterone-pretreatment: Prior to introduction rams of ½ of the ewe lambs in each nutrition plane will be pre-treated with progesterone containing CIDR devices for 5 days, the other ½ of the ewes will not be treated. Previous research, as well as our preliminary data using FDA approved progesterone containing CIDR devices indicate that pre-treatment with progesterone increases fertility of ewe lambs and it may have an additive effect with heavier weight at breeding.
METHODS
A 2x2 factorial arrangement of treatment will be used to determine the effect of weight at breeding and
progesterone pre-treatment on the fertility of replacement ewe lambs. Ewe lambs (N = 900-1000) on 10-15 farms ranging in age from 5-10 months by September will be randomly assigned within age (5,6,7,8, 9 or >10 months) to the High (HP) or Low (LP) plane of nutrition treatment for 60 days projected to produce live weight gains of 20-25lbs and 10-12 lbs, respectively. Beginning in December half of the ewe lambs in each nutritional plane treatment group would be assigned to either receive progesterone via CIDR devices (HPCIDR, LPCIDR) or remain untreated (HPControl, LPControl). Following CIDR removal rams with harnesses with crayons would be introduced to ewe lambs (< 25 :1, female to ram ratio) for a 35 day breeding period. Observation for raddle marks would be used to assess the occurrence of estrus. Blood samples and ewe lamb weights would be taken at the start of the experiment and at biweekly intervals. Ultrasonography would be conducted at days 25-30 and 45-50, 65-75, 90-100 after introduction of rams to detect pregnancy and embryonic survival and lambing data would be recorded at birth.
DATA COLLECTION
Blood samples would be analysed for progesterone as an indicator of puberty (> 1 ng/ml), and AMH as a potential indicator of ewe lamb fertility. The effect of feeding program (HP, LP) and progesterone pre-treatment (CIDR, Control) and their interaction would be used to determine the effect on estrus, response, pregnancy rate, embryonic survival, percent ewes lambing, prolificacy, lambing rate and total lamb birth weight. Pooled data would be used to determine the effect of weight gain, weight at breeding, concentration of AMH (high vs low, 50 percentile) on reproductive performance variables. Cost of all inputs for treatment combinations and value of lambs produced and cost saved would be determined and used in economic analyses. Continuous variables will be analyzed using the GLM procedure of SAS, where interactions are present means would be separated using Tukey’s HSD. Categorical data would be analyzed using contingency Chi Square
Experiment 3:
OBJECTIVE:
To evaluate the effects of pre-breeding nutritional management and weight changes on ewe lamb fertility.
MATERIALS AND METHODS:
Materials
The procedures used in these studies were approved by the West Virginia University Animal Care and Use Committee (IACUC #___). The Controlled Internal Drug Release Device (CIDR) was obtained from Zoetis Animal Health, Kalamazoo, MI.
Replicate 1:
Farm and animals
Research was conducted during the breeding seasons of 2014 and 2015 at West Virginia University’s Reymann Memorial Farm in eastern West Virginia and at Wherry Farm in Scenery Hill, Pennsylvania.
A total of 126 Dorset X Texel (DT) ewe lambs and 69 Katahdin (KD) ewe lambs were utilized. At the start of the experiment, DT lambs were on average 6.6 ± 0.1 months of age and 36.9 ± 0.7 kg; whereas, KD lambs averaged 4.8 ± 0.2 months of age and 23.3 ± 0.8 kg liveweight. All animals were reared on pasture with ad libitum forage and water, and supplemented concentrate.
Experimental protocol
Lambs were randomly selected to receive either high (0.68 kg/head/day) or low (0.23 kg/head/day) grain supplementation containing 14% crude protein. Respective diets were supplemented for two months prior to estrous synchronization and live weights were recorded biweekly. Weight data
were used to calculate changes in weight for the supplementation period, average daily gains for the treatment period, and lifetime average daily gains.
Prior to ram introduction (d-5), half of each treatment group were randomly selected to receive a progesterone pretreatment using an intravaginal CIDR (ZOETIS EAZI-BREED™ CIDR® 0.3g progesterone). Progesterone treatment was removed on d0 prior to ram introduction. All rams had fertility previously proven and were equipped with marking harnesses to determine estrous response.
Replicate 2:
Farm and animals
Research was conducted during the breeding season of 2016 at two affiliate farms: one located in southern Pennsylvania and one located in north central West Virginia.
A total of 125 Dorset X Texel (DT) ewe lambs ewe lambs were utilized for experimentation. All animals were reared on pasture with ad libitum forage and water, and supplemented concentrate according to the respective treatment group.
Experimental protocol
Lambs were randomly selected to receive either high (0.91 kg/head/day) or low (0.45 kg/head/day) grain supplementation (14% crude protein). Respective diets were supplemented for four weeks prior to estrous synchronization and liveweights were recorded biweekly. Weight data was utilized to calculate changes in liveweight, average daily gains, and agerage daily gains for the life of each lamb.
Blood collection and progesterone quantification
Blood samples were collected bi-weekly via jugular venipuncture at the start of the feeding period until CIDR insertion to determine if the ewe lambs were cycling at the begging of the experiment and if they were cycling at breeding. Blood samples were collected into heparinized tubes (EDTA; Monoject, 15% EDTA K3 liquid, Tyco Healthcare Group, Mansfield, Massachusetts, USA) and centrifuged for 20 minutes at 3000 rotations per minute. Plasma was harvested and stored at -20ᵒC until quantification of progesterone via I-125 radioimmunoassay (ImmuChem™ Double Antibody Progesterone 125-1 RIA Kit, MP Biomedicals, Costa Mesa, CA). Progesterone concentration was measured in individual plasma samples and expressed in terms of nanograms per milliliter (ng/ml). Values of greater than 1 ng/ml indicated puberty and was used to determine ovulatory status of each female.
Estrous detection and ultrasonography
Estrous response was determined by observation of raddle marks 96 hours after ram introduction. Following synchronization of estrus, pregnancy diagnosis using transrectal ultrasonography (Aloka 500 Corometrics Medical Systems, Wallingford, CT, USA with a 7.5 MHz linear transducer) was conducted one month after ram introduction and overall pregnancy was determined two months after ram introduction. Lambing data was recorded. This data was used to determine conception rates, pregnancy to first service, overall pregnancy rates, and lambing rates.
Breeding weight category, average daily gains category, and weight day average category
Animals within each respective breed were classified by breeding weight, average daily gains for the treatment period, and weight day averages to determine their effects on reproductive responses. Groups were divided by calculating the mean ± one half of the standard deviation: light: L < µ- ½ STD, moderate: µ- ½ STD < M < µ+ ½ STD, heavy: He > µ+ ½ STD. Characteristics of each breed for breeding weight category, average daily gain category, and weight day average category are reported in Table 1.
Table 1 Description of ewe lamb characteristics
|
|
Replicate 1 |
Replicate 2 |
Replicate 3 |
|
|
Dorset X |
Katahdin |
Dorset X |
Dorset X |
|
|
Breeding Weight Category (kg) |
||||
|
Heavy |
51.4±0.4 |
36.6±0.7 |
47.1±0.4 |
|
|
Moderate |
40.1±0.4 |
30.1±0.3 |
41.6±0.4 |
|
|
Light |
32.8±0.6 |
23.4±0.5 |
35.4±0.4 |
|
|
|
Average Daily Gain Category (g) |
|||
|
Heavy |
138±3 |
163±10 |
99±6 |
|
|
Moderate |
67±3 |
100±7 |
43±5 |
|
|
Light |
-27±5 |
53±7 |
-34±6 |
|
|
|
Weight Day Average Category (g) |
|||
|
Heavy |
198±2 |
176±4 |
|
198±2 |
|
Moderate |
159±2 |
148±4 |
|
159±2 |
|
Light |
117±2 |
116±2 |
|
117±2 |
Pooled Replicate:
Dorset X Texel cross ewe lambs from both replicates were pooled for statistical analysis to determine the main effects of nutritional treatment, progesterone pretreatment, breeding weight category, average daily gain category, weight day average category, and each respective interaction. on this specific breed.
Statistical analysis
A two-way Analysis of Covariance (ANCOVA) was conducted using the PROC MIX procedure of SAS (Statistical Analysis System version 9.4 for Windows; SAS Institute, Cary, NC, USA) to determine the effect of nutritional treatment group, breed, progesterone pretreatment, breeding weight category, average daily gain category, weight day average category, and each respective interaction. Breeding age was used as a covariate in the statistical model to increase the power to detecting treatment effects. Additionally, an ANCOVA using the PROC MIXED procedure with breeding age as a covariate was used on the pooled replicate to determine if breeding weight, average daily gain for the treatment period, and weight day average differed in lambs experiencing a positive of negative reproductive outcome. All one degree comparisons were conducted using Tukey’s LSD. All results are presented as least squares means ± the standard error of the mean (LS Means ± SEM). Results were considered significant at a confidence level of P < 0.05, and a tendency when 0.05 < P < 1.0
Experiment 1: Effect of stimulation with a gonadotropin mixture on reproductive outcome in nulliparous ewes bred during seasonal anestrus and early breeding season:
- Fall-born ewe lambs and spring-born yearling nulliparous ewes can be successfully bred during the non-breeding season when pre-treated with progesterone prior to introduction of rams (Tables 1 and 2). Further gonadotropin stimulation at progesterone withdrawal improves the reproductive outcome in fall-born ewe lambs (Table 1) but not in spring-born yearling nulliparous ewes (Table 2) bred during the non-breeding season. In fall-born ewe lambs bred during the anestrous period (Table 1), gonadotropic stimulation increased estrous response (P = 0.0002), pregnancy rate to the first service period (P = 0.0007), proportion of ewes lambing to the first service period, proportion lambing overall (P = 0.03) and the lambing rate (P = 0.01). Treatment decreased the number of days from ram introduction to lambing (P = 0.05) and the mean lambing day (P = 0.02). The mean conception rate (81.5 ± 3.5%) and the proportion of fall-born ewe lambs lambing to the second service period (3.2 ± 1.3%) were not affected by gonadotropin stimulation. Gonadotropic stimulation increased estrous response (P = 0.03; Table 2) but did not modify other measures of reproductive performance in yearling females exposed to rams during seasonal anestrus.
- Progesterone pre-treatment without gonadotropin stimulation is sufficient to improve reproductive outcome in spring-born yearling nulliparous ewes bred during the breeding season (Table 3). During the transition into the breeding season, progesterone pre-treatment increased the proportion of yearling females exhibiting estrus during the first 3 days after ram introduction (P = 0.0001), pregnancy rate and proportion of females lambing to the first service period (P = 0.003 and P = 0.02, respectively; Table 3). The proportion of females lambing to the second service period was lower in progesterone-pretreated yearlings (P = 0.05; Table 3). Gonadotropic stimulation of progesterone pre-treated yearlings decreased the proportion of females lambing to the first service period (P = 0.02; Table 3) but did not modify other reproductive performance variables measured.
Table 1: Effect of gonadotropic stimulation with 240IU of eCG and 120IU of hCG (P.G. 600®) administered on the last day of a 5-day progesterone pre-treatment on reproductive responses in fall-born ewe lambs exposed to rams during the mid-anestrus (Study 1).
|
Variable |
Treatment |
P-value |
|
|
CIDR |
CIDR+P.G. 600® |
||
|
n |
95 |
95 |
|
|
Estrous response (%) |
52.6 ± 4.7 (n = 95) |
77.9 ± 4.7 (n = 95) |
0.0002 |
|
Conception rate (%) |
78 ± 5.5 (n = 50 ) |
83.7 ± 4.5 (n = 74) |
NS |
|
Pregnancy rate (%) 1st service a |
41.1 ± 5.0 (n = 95 ) |
65.3 ± 5.0 (n = 95) |
0.0007 |
|
Prolificacy first service b |
1.31 ± 0.1 (n = 36) |
1.5 ± 0.08 (n = 51) |
NS |
|
Overall Prolificacy |
1.32 ± 0.1 (n = 38 ) |
1.47 ± 0.08 (n = 53) |
NS |
|
Lambing to 1st service (%)c |
37.9 ± 5.1 (n = 95 ) |
53.7 ± 5.1 (n = 95 ) |
0.03 |
|
Lambing to 2nd service (%)d |
4.2 ± 1.8 (n = 95 ) |
2.1 ± 1.8 (n = 95 ) |
NS |
|
Pregnancy retention 1st service (%)e |
92.3 ± 5.2 (n = 39 ) |
85.5 ± 4.1 (n = 62) |
NS |
|
Proportion of females lambing (%) |
40.0 ± 5.1 (n = 95 ) |
55.8 ± 5.1 (n = 95) |
0.03 |
|
Lambing rate (%) f |
52.6 ± 8.3 (n = 95 ) |
82 ± 8.2 (n = 95) |
0.01 |
|
Ram introduction to lambing (d)g |
148.6 ± 0.5 (n = 38) |
147.3 ± 0.4 (n = 53) |
0.05 |
|
Lambing day (d) h |
8.4 ± 0.5 (n = 38) |
6.8 ± 0.4 (n = 53) |
0.02 |
Not all variables were measured for all animals. n’s are indicated for each variable under treatment groups.
aNumber of ewes diagnosed pregnant on day 30 to 35 as a percentage of all ewes exposed to rams.
bLambs born per ewe lambing to the first service period (first 14 days of lambing season.)
cProportion of ewes lambing by day 14 of the lambing period.
dProportion of ewes lambing between day 15 to day 30 of the lambing period.
eEwes lambing that were diagnosed pregnant to the first service period.
fLambs born per ewe exposed to rams.
g Mean number of days from ram introduction to lambing.
h Mean day ewe gave birth within the lambing period (day 1 = day the first ewe lambed).
Values are least squares means ± SEM (number of animals).
Table 2: Effect of gonadotropic stimulation with 240IU of eCG and 120IU of hCG (P.G. 600®) administered on the last day of a 5-day progesterone pre-treatment on reproductive responses in yearling nulliparous ewes exposed to rams during the mid-anestrus (Study 2).
|
Variable |
Treatment |
P-value |
|
|
CIDR |
CIDR+P.G. 600® |
||
|
n |
61 |
59 |
|
|
Age (days) |
446.9 ± 6 |
433.6 ± 5.8 |
|
|
Estrous response (%) |
80.3 ± 4.3 |
93.2 ± 4.3 |
0.03 |
|
Conception rate (%) |
69.4 ± 6.6 |
70.9 ± 6.3 |
NS |
|
Pregnancy rate (%) 1st service a |
55.7 ± 6.2 |
66.1 ± 6.3 |
NS |
|
Prolificacy 1st service b |
1.46 ± 0.1 |
1.48 ± 0.1 |
NS |
|
Overall Prolificacy |
1.38 ± 0.1 |
1.47 ± 0.09 |
NS |
|
Lambing to 1st service (%)c |
42.4 ± 6.5 |
43.1 ± 6.6 |
NS |
|
Lambing to 2nd service (%)d |
8.2 ± 3.6 |
8.5 ± 3.6 |
NS |
|
Pregnancy retention 1st service (%)e |
73.5 ± 8 |
65.8 ± 7.6 |
NS |
|
Proportion of females lambing (%) |
50.8 ± 6.6 |
51.7 ± 6.6 |
NS |
|
Lambing rate (%) f |
70 ± 10.7 |
75.9 ± 10.7 |
NS |
|
Ram introduction to lambing (d)g |
147.1 ± 1.17 |
147.1 ± 1.17 |
NS |
|
Lambing day (d) h |
9.1 ± 1.17 |
9.1 ± 1.17 |
NS |
aNumber of ewes diagnosed pregnant on day 33 as a percentage of all ewes exposed to rams.
bLambs born per ewe lambing to the first service period (first 14 days of lambing season).
cProportion of ewes lambing by day 14 of the lambing period.
dProportion of ewes lambing between day 15 to day 30 of the lambing period
eEwes lambing that were diagnosed pregnant to the first service period.
fLambs born per ewe exposed to rams.
g Mean number of days from ram introduction to lambing.
h Mean day ewe gave birth within the lambing period (day 1 = day the first ewe lambed).
Values are least squares means ± SEM.
Table 3: Effect of progesterone pre-treatment and gonadotropin stimulation with 240IU of eCG and 120IU of hCG (P.G. 600®) administered at progesterone removal on reproductive responses in spring-born yearling ewes exposed to rams during late anestrus/early breeding season (Study 3).
|
Variable |
Treatment |
P-Value |
|||
|
|
Control |
CIDR |
CIDR+ P.G.600® |
Control vs CIDR |
CIDRPG vs CIDR |
|
n |
30 |
31 |
32 |
|
|
|
Age |
509 ± 8.9 |
512 ± 9.1 |
510 ± 8.6 |
NS |
NS |
|
Estrous response (%) |
16.6 ± 8.1 |
61.3 ± 8.0 |
71.9 ± 7.8 |
0.0001 |
NS |
|
Conception rate (%) |
50.0 ± 25.8 |
52.9 ± 12.5 |
47.8 ± 10.8 |
NS |
NS |
|
Pregnancy rate (%) 1st service a |
10.0 ± 8.1 |
45.2 ± 8.0 |
34.4 ± 7.8 |
0.003 |
NS |
|
Pregnancy rate (%) 2nd service b |
44.8 ± 9.3 |
58.1 ± 9.0 |
43.8 ± 8.9 |
NS |
NS |
|
Pregnancy rate (%) 3rd service c |
72.4 ± 8.4 |
71 ± 8.1 |
74.2 ± 8.1 |
NS |
NS |
|
Pregnancy rate (%) 4th service d |
80.0 ± 7.4 |
87.1 ± 7.3 |
71 ± 7.3 |
NS |
NS |
|
Prolificacy 1st service e |
1.50 ± 0.3 |
1.2 ± 0.1 |
1.6 ± 0.2 |
NS |
NS |
|
Overall Prolificacy |
1.52 ± 0.1 |
1.35 ± 0.1 |
1.33 ± 0.1 |
NS |
NS |
|
Lambing to 1st service (%)f |
6.9 ± 7.2 |
38.7 ± 7.0 |
18.1 ± 7.0 |
0.02 |
0.02 |
|
Lambing to 2nd service (%)g |
34.5 ± 7.7 |
16.1 ± 7.4 |
18.1 ± 7.4 |
0.05 |
NS |
|
Lambing to 3rd service (%)h |
40 ± 8.4 |
25.8 ± 8.2 |
25 ± 8.2 |
NS |
NS |
|
Proportion of females lambing (%) |
76.7 ± 7.6 |
86.7 ± 7.6 |
66.7 ± 8.1 |
NS |
0.08 |
|
Lambing rate (%) i |
101 ± 13.6 |
113 ± 13.6 |
88.9 ± 14.3 |
NS |
NS |
|
Ram introduction to lambing (d)j |
178 ± 4.5 |
172 ± 4.2 |
170 ± 5.2 |
NS |
NS |
|
Lambing day (d)k |
33 ± 4.5 |
25.1 ± 4.3 |
24.6 ± 5.2 |
NS |
NS |
a-dNumber of ewes diagnosed pregnant on day 35, 50, 75 and 90 respectively, as a percentage of all ewes exposed to rams.
eLambs born per ewe lambing to the first service period (first 14 days of lambing season).
fProportion of ewes lambing by day 14 of the lambing period.
gProportion of ewes lambing between day 15-30 of the lambing period.
hProportion of ewes lambing after day 30 of the lambing period.
iLambs born per ewe exposed to rams.
J Mean number of days from ram introduction to lambing.
K Mean day ewe gave birth within the lambing period (day 1 = day the first ewe lambed).
Values are least squares means ± SEM.
Experiment 2: The relationship between the concentration of anti-mullerian hormone (AMH) and fertility in replacement females
2.1 Relationship between concentration of AMH, breed and age
The mean breeding age of the replacement females were 8.3 ± 0.01 months. The mean systemic concentration of AMH for Dorset, Katahdin and Suffolk replacement females were 337 ± 14, 566 ± 37 and 237 ± 22 pg/ml, respectively. AMH was higher in Katahdin replacement females than Dorset and Suffolk replacement females (P < 0.001). AMH decreased linearly with age (Figure 4a; P = 0.03) in Dorset/Texel replacements with age but there was no relationship between age and AMH in Katahdin replacement females (Figure 4b).
2.2 Relationship between concentration of AMH and reproductive outcomes in Dorset and Katahdin replacement females
There was a significant interaction of breed x AMH on conception rate (Table 5: P = 0.02) and lambing to the first service (Table 5; P = 0.01). More Katahdin replacement females with HIGH AMH conceived (P = 0.005; 90.0 ± 13.0 vs. 41.6 ± 11.9 %) and lambed to the first service period (P = 0.004; 90.6 ± 15.4 vs. 31.5 ± 13.6 %) compared to Katahdin females with LOW AMH. However, conception rate and proportion of females lambing to the first service did not differ among Dorset replacement females with LOW, MEDIUM and HIGH AMH.
Dorset replacement females (Table 6) had a higher estrous response (P = 0.01), pregnancy rate to first service (P = 0.002), pregnancy rate to second service (P = 0.002), prolificacy to first service (P = 0.03), percentage lambed (P < 0.001) and lambing rate (P < 0.001) than Katahdin replacement females. In addition, Dorset females tended to have a higher conception rate (P = 0.08) and overall prolificacy (P = 0.09) than Katahdin females.
More replacement females with HIGH AMH lambed to the first service period compared to females with LOW and MEDIUM AMH (Table 6; P = 0.04). Replacement females with HIGH AMH tended to have a higher conception rate (P = 0.07) lower number of days from ram introduction to lambing (P = 0.07), lambed earlier within the lambing period (P = 0.08) and lower age to first lambing (P = 0.08).
2.3 AMH Concentrations in plasma according to binary reproductive responses
AMH was higher in replacement females that conceived (P = 0.01; 471 ± 25 vs. 360 ± 37 pg/ml) compared to females that did not conceive. There was a significant interaction (Table 7; P = 0.0007) of breed x conception. Katahdin replacement females that conceived had a higher (P = 0.0008) concentration of AMH compared to Katahdin females that did not conceive. However, AMH did not differ between Dorset replacement females that conceived and Dorset females that did not conceive.
There was a significant interaction (Table 7; P = 0.009) of breed x pregnancy to the first service on AMH. Dorset replacement females that were pregnant to the first service had a lower (P = 0.03) AMH compared to Dorset females with HIGH that did not become pregnant to the first service.
AMH was higher in replacement females that lambed to the first service (P = 0.005; 507 ± 29 vs. 382 ± 34 pg/ml) compared to replacement females that did not lamb to the first service. There was a significant interaction (Table 7; P = 0.0009) of breed x lambing to first service. Katahdin replacement females that lambed to the first service had a higher (P = 0.0007) concentration of AMH compared to Katahdin females that did not lamb to the first service. However, AMH did not differ between Dorset replacement females that lambed to the first service and Dorset females that did not lamb to the first service.
Table 4: Concentration of AMH used to classify animals as low, medium and high and total number of animals
|
Breed |
Concentration of AMH (pg/ml)
|
N |
||
|
Low |
Medium |
High
|
|
|
|
Dorset |
< 227 (n = 89) |
227 – 447 (n = 89) |
> 447 (n = 60) |
238
|
|
Katahdin |
< 403 (n = 24) |
403 – 728 (n = 33) |
> 728 (n = 20) |
77
|
|
Suffolk |
< 164 (n = 17) |
164- 311 (n=18) |
> 311 (n= 9) |
44
|
Table 5: Effect of breed (Dorset/Texel Crosses, n = 238 and Katahdin, n = 77) and concentration of AMH (Low, Medium and High) on reproductive responses of replacement females. Values are least square means ± SEM. Significant interaction P < 0.05.
|
Reproductive Variable |
Breed of Replacement female (B)
|
P-value |
|||||
|
Dorset/Texel Cross |
Katahdin
|
||||||
|
Concentration of AMH (pg/ml)
|
|||||||
|
Low |
Medium |
High |
Low |
Medium |
High |
Interaction (B x AMH) |
|
|
Conception rate (%)a
|
81.2 ± 5.0 |
84.1 ± 4.9 |
75.7 ± 6.7 |
41.6 ± 11.9 |
66.6 ± 10.7 |
90.0 ± 13.0 |
0.02 |
|
Pregnancy rate (%) 1st serviceb
|
61.8 ± 5.3 |
64.9 ± 5.1 |
46.4 ± 6.3 |
25.7 ± 10.8 |
34.2 ± 9.0 |
46.8 ± 11.0 |
0.07 |
|
Prolificacy 1st servicec
|
1.34 ± 0.08 |
1.23 ± 0.07 |
1.32 ± 0.1 |
1.03 ± 0.23 |
1.04 ± 0.17 |
1.03 ± 0.17 |
0.09 |
|
Lambing to 1st service (%)d
|
59.4 ± 6.7 |
68.1 ± 6.1 |
53.6 ± 7.8 |
31.5 ± 13.6 |
62.4 ± 13.7 |
90.6 ± 15.4 |
0.01 |
|
Table 6: Main effects of breed (Dorset/Texel crosses, n = 238 and Katahdin, n = 77) and concentration of AMH (Low, Medium and High) on reproductive responses of replacement females. Significant difference P < 0.05.
|
Reproductive Response |
Breed of Replacement Female
|
Concentration of AMH (pg/ml) |
P-Value |
||||
|
Dorset/Texel Cross |
Katahdin
|
Low (L) |
Medium (M) |
High (H) |
Breed |
AMH H vs. L
|
|
|
Estrous Response (%)a
|
71.5 ± 3.0 |
54.4 ± 5.9 |
67.8 ± 5.5 |
64.1 ± 4.8 |
56.9 ± 5.9 |
0.01 |
NS |
|
Conception rate (%)b
|
80.3 ± 3.2 |
66.1 ± 7.2 |
61.4 ± 4.4 |
75.3 ± 5.9 |
82.8 ± 7.3 |
0.08 |
0.07 |
|
Pregnancy rate (%) 1st servicec
|
57.7 ± 3.3 |
35.6 ± 6.2 |
43.8 ± 5.9 |
49.6 ± 6.3 |
46.6 ± 6.3 |
0.002 |
NS |
|
Pregnancy rate (%) 2nd serviced
|
82.3 ± 2.7 |
63.0 ± 5.3 |
74.2 ± 5.0 |
72.2 ± 4.5 |
71.5 ± 5.3 |
0.002 |
NS |
|
Prolificacye
|
1.18 ± 0.04 |
1.03 ± 0.08 |
1.11 ± 0.07 |
1.10 ± 0.07 |
1.09 ± 0.07 |
0.09 |
NS |
|
Prolificacy 1st servicef
|
1.30 ± 0.05 |
1.03 ± 0.11 |
1.19 ± 0.12 |
1.13 ± 0.09 |
1.17 ± 0.09 |
0.03 |
NS |
|
Lambing to 1st service (%)g
|
60.4 ± 4.0 |
61.5 ± 8.4 |
45.5 ± 7.5 |
65.2 ± 7.4 |
72.1 ± 8.6 |
NS |
0.04 |
|
Lambed (%)
|
68.7 ± 3.1 |
41.0 ± 5.9 |
60.5 ± 5.5 |
51.9 ± 5.0 |
52.1 ± 6.0 |
< 0.001 |
NS |
|
Lambing rate (%)h
|
83.9 ± 4.2 |
39.9 ± 8.1 |
68.2 ± 7.6 |
58.7 ± 6.8 |
58.7 ± 8.1 |
< 0.001 |
NS |
|
Ram introduction to lambing (d)i
|
155.9 ± 0.9 |
159.04 ± 2.0 |
160.7 ± 1.7 |
155.4 ± 1.7 |
156.3 ± 2.0 |
NS |
0.08 |
|
Lambing day (d)j
|
14.6 ± 0.9 |
13.6 ± 2.0 |
17.4 ± 1.8 |
12.1 ± 1.8 |
12.8 ± 2.0 |
NS |
0.08 |
|
Age to first lambing (d)
|
398.61 ± 1.71 |
401.60 ± 1.9 |
403.3 ± 1.7 |
398.2 ± 1.7 |
398.8 ± 2.0 |
NS |
0.08 |
aNumber of replacement females marked by rams of all ewe lambs exposed
bNumber of replacement females diagnosed pregnant as a percentage of ewe lambs marked by rams
cNumber of replacement females diagnosed on day 30 to 35 as a percentage of all ewe lambs exposed to rams
dNumber of replacement females diagnosed on day 50 to 55 as a percentage of ewe lambs not pregnant on day 30 -35
eLambs born per replacement female lambing
fLambs born per replacement female lambing to the first service period (first 14 days of lambing season)
gProportion of replacement females lambing by day 14 of the lambing period
hLambs born per replacement female exposed
IMean number of days from ram introduction to lambing
JMean day replacement female gave birth within the lambing period (day 1 = day the first ewe lambed).
Table 7: The relationship between concentration of AMH and reproductive responses in Dorset/Texel crosses (n = 238) and Katahdin breed (n = 77) ewe lambs. Values are least square means ± SEM. Significant difference and interaction P < 0.05.
|
Reproductive Response (RR) |
Breed of Replacement Female
|
P – Value |
|||||
|
Dorset/Texel Cross
|
Katahdin |
||||||
|
Incidence of Event AMH Concentration (pg/ml) |
Reproductive Response (RR)
|
Breed (B) |
Interaction (B X RR) |
||||
|
|
Yes |
No |
Yes
|
No |
|
|
|
|
Estrous Response
|
316.30 ± 18.7 |
395.8 ± 31.3 |
559.2 ± 40.8 |
571.70 ± 39.2 |
NS |
< 0.001 |
NS |
|
Conceptiona |
313.0 ± 19.0 |
355.5 ± 39
|
629.8 ± 47 |
365.5 ± 64 |
0.01 |
0.0006 |
0.0007 |
|
Pregnancy to 1st serviceb |
315.9 ± 21.1 |
384.7 ± 25.3
|
632.8 ± 51 |
519.0 ± 37 |
NS |
< 0.001 |
0.009 |
|
Lambing to 1st servicec |
330.4 ± 24.3 |
354.7 ± 30.7
|
683.3 ± 52.7 |
408.7 ± 62.0 |
0.005 |
< 0.001 |
0.0009 |
|
Lambed
|
335.3 ± 20.1 |
362.5 ± 30.4
|
534.8 ± 42.8 |
573.2 ± 45.5 |
NS |
< 0.001 |
NS |
aNumber of replacement females diagnosed pregnant and marked by rams
bNumber of replacement females diagnosed pregnant on day 30 to 35 of all ewes exposed to rams
cNumber of replacement females lambing by day 14 of the lambing period
Experiment 3:
RESULTS:
Replicate 1:
Breed, nutritional treatment, and progesterone pretreatment
There was a significant breed effect for pregnancy to first service, and proportion having exhibited estrous cyclicity prior to breeding (Table 2). However, there was no significant effect of breed on overall fertility as indicated by the results of the overall pregnancy rate, proportion lambing, and prolificacy.
Additionally, there was no significant effect of nutritional treatment on overall fertility (Table 2). There was a tendency for the elevated plane of nutrition females to have an increased prolificacy and there tended (P=0.1265) to be an interaction between nutrition and breed for estrous response primarily due to a difference in the Dorset X high and Katahdin X high nutritional treatment groups being significantly different (P=0.0014, 75±4 v 49±7).
There was no significant effect of progesterone pretreatment on reproductive responses (Table 2). Though, there was a significant difference in the proportion of females that had initiated cyclicity prior to breeding. A greater proportion of ewe lambs that did receive a CIDR had initiated cyclicity prior to breeding.
There tended to be an interaction between CIDR and Breed (0.0514) for conception rate due to a significant difference between DT and KT females that did not receive a CIDR having various conception rates (P= 0.0073, 85±5 v 53±10% respectively), and no difference in conception rate for KT that did and did not receive a CIDR (73±10 v 53±10% P=0.1679). There was a significant CIDR by breed interaction for PD1 (P=0.0320) due to there being no difference in the KT proportion pregnant to PD1 no differing between the KT that received a CIDR (30±8 v 44±9, P=0.2215). There tended to be a breed by CIDR interaction for puberty at breeding (P=0.0839) due to a strong significance between the DT females that did and did not receive a CIDR (20±3 v 9±7, P<0.0001), a lack of significant difference between the number of KT females that did and did not receive a CIDR (5±7 v 9±7 P=0.6607).
Breeding Weight Category
Animals that were heavier at breeding exhibited a significant effect on reproductive response by increasing estrous response, pregnancy rates, proportion lambing, and lambing rate, and decreasing the average age at first lambing (Table 3). However, there tended to be a breed X breeding weight interaction for estrous response, and there was a significant breed by breeding weight interaction for conception rate, pregnancy to first service, and age at first lambing.
Average daily gain category
There was no difference in estrous response for the different average daily gain categories; however, animals that grew at a faster rate during the immediate prebreeding period tended to have an increase conception rate (Table 4). These animals exhibited a significantly greater proportion pregnant to the first service period, a greater proportion lambing, and an increased lambing rate compared to those that grew at a slower rate during the treatment period. There were no significant interactions between breed and ADG categories for any reproductive response.
Weight day average category
Increased weight day averages significantly increased fertility response (Table 5). The animals that averaged the moderate to the highest weight day averages had a greater estrous response, pregnancy to first service, overall pregnancy rate, proportion lambing, lambing rate, and proportion achieve puberty by breeding. Additionally, there was a significant interaction for breed X weight day average category for various reproductive responses.
Table 2 Effects of breed (Dorset X v Katahdin), nutritional treatment (High v Low), and progesterone pretreatement on reproductive responses in nulliparous female sheep prior to breeding.
|
|
Breed |
Nutritional Treatment |
Progesterone Pretreatment |
||||||
|
Dorset |
Katahdin |
p-value |
High |
Low |
p-value |
Yes |
No |
p-value |
|
|
Age at breeding (months) |
9.1±0.1 |
6.9±0.2 |
<0.0001 |
8.0±0.2 |
8.0±0.2 |
NS |
8.7±0.1 |
8.7±0.02 |
NS |
|
Weight at breeding (kg) |
43.2±0.5 |
29.5±0.9 |
<0.0001 |
42.9±0.7 |
41.2±0.7 |
NS |
|
|
0.0655 |
|
Average daily gain (g) |
77±4 |
97±8 |
<0.0001 |
160±7 |
135±7 |
0.0075 |
|
|
|
|
Estrous response (%) |
74±3 |
57±6 |
0.0057 |
62±4 |
69±4 |
NS |
66±4 |
66±4 |
NS |
|
Conception rate (%) |
77±3 |
63±8 |
0.0939 |
66±6 |
74±5 |
NS |
73±5 |
69±6 |
NS |
|
Pregnancy 1st service (%)a |
57±3 |
38±6 |
0.0049 |
43±4 |
52±5 |
NS |
49±5 |
49±5 |
NS |
|
Pregnancy overall (%) |
75±3 |
65±6 |
NS |
70±4 |
70±5 |
NS |
75±4 |
65±4 |
0.0988 |
|
Proportion lambing (%) |
60±3 |
54±6 |
NS |
56±4 |
58±5 |
NS |
60±5 |
56±5 |
NS |
|
Lambing rate (%)b |
69±4 |
60±8 |
NS |
67±6 |
63±7 |
NS |
68±6 |
63±6 |
NS |
|
Age 1st lambing (days) |
420±1 |
423±2 |
NS |
422±1 |
421±1 |
NS |
421±1 |
422±1 |
NS |
|
Number born |
1.18±0.03 |
1.10±0.06 |
NS |
1.2±0.046 |
1.1±0.5 |
0.0936 |
1.1±0.05 |
1.1±0.05 |
NS |
|
Puberty by breeding (%) |
26±2 |
8±5 |
0.0031 |
16±4 |
18±4 |
NS |
13±4 |
26±4 |
0.0121 |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 3 Effect of breeding weight on reproductive responses in nulliparious females of the Dorset X and Katahdin breeds.
|
|
Dorset |
Katahdin |
P-Value |
|||||||
|
Heavy |
Medium |
Light |
Heavy |
Medium |
Light |
H v M |
M v L |
H v L |
Breed X WtDayAve |
|
|
Estrous response (%) |
90±4 |
72±4 |
49±5 |
59±9 |
68±8 |
41±9 |
NS |
0.0004 |
<0.0001 |
0.0987 |
|
Conception rate (%) |
89±4 |
74±4 |
46±7 |
59±12 |
60±10 |
76±15 |
NS |
NS |
NS |
0.0147 |
|
Pregnancy 1st service (%)a |
80±4 |
53±4 |
23±6 |
35±10 |
40±9 |
31±10 |
0.1202 |
0.0074 |
<0.0001 |
0.0020 |
|
Pregnancy overall (%) |
86±4 |
76±4 |
50±5 |
71±9 |
75±8 |
43±9 |
NS |
<0.0001 |
<0.0001 |
NS |
|
Proportion lambing (%) |
71±4 |
62±4 |
42±6 |
58±10 |
62±10 |
35±11 |
NS |
0.0033 |
0.0015 |
NS |
|
Lambing rate (%)b |
90±6 |
67±6 |
43±8 |
61±14 |
69±12 |
39±14 |
NS |
0.0085 |
0.0012 |
NS |
|
Age 1st lambing (days) |
418±1 |
419±1 |
432±2 |
426±3 |
423±3 |
421±4 |
NS |
0.0317 |
0.0747 |
0.0013 |
|
Number born |
1.29±0.04 |
1.1±0.04 |
1.03±0.08 |
1.0±0.10 |
1.1±0.09 |
1.0±0.10 |
NS |
NS |
NS |
NS |
|
Puberty by breeding (%) |
39±4 |
21±4 |
11±5 |
10±9 |
6±8 |
6±9 |
0.0761 |
NS |
0.0161 |
NS |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 4 The reproductive responses of the average daily gains category.
|
|
Average Daily Gain Category |
|
||||
|
Heavy |
Medium |
Light |
H v M |
M v L |
H v L |
|
|
Estrous response (%) |
73±6 |
66±4 |
61± |
NS |
NS |
NS |
|
Conception rate (%) |
76±7 |
72±6 |
57±7 |
NS |
0.0941 |
0.0550 |
|
Pregnancy 1st service (%)a |
56±6 |
49±5 |
36±6 |
NS |
0.0772 |
0.0204 |
|
Pregnancy overall (%) |
70±6 |
72±4 |
63±6 |
NS |
NS |
NS |
|
Proportion lambing (%) |
65±7 |
60±5 |
45±6 |
NS |
0.0508 |
0.0223 |
|
Lambing rate (%)b |
79±9 |
64±6 |
51±8 |
NS |
NS |
0.0162 |
|
Age 1st lambing (days) |
420±2 |
423±1 |
423±2 |
NS |
NS |
NS |
|
Number born |
1.2±0.06 |
1.1±0.04 |
1.1±0.07 |
0.0609 |
NS |
NS |
|
Puberty by breeding (%) |
18±5 |
19±4 |
12±5 |
NS |
NS |
NS |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 5 Reproductive responses of weight day average category by breed.
|
Reproductive Response |
WT day ave Category |
|
Breed X Weight/ Day Average |
|||||||
|
Dorset |
Katahdin |
|||||||||
|
Heavy |
Medium |
Light |
Heavy |
Medium |
Light |
H v M |
M v L |
H v L |
||
|
Estrous response (%) |
89±4 |
78±4 |
39±5 |
67±9 |
80±9 |
55±8 |
NS |
<0.0001 |
<0.0001 |
0.0216 |
|
Conception rate (%) |
90±4 |
71±5 |
54±8 |
64±13 |
69±11 |
81±13 |
NS |
NS |
NS |
0.0301 |
|
Pregnancy 1st service (%)a |
77±4 |
56±5 |
19±6 |
44±10 |
56±10 |
45±9 |
NS |
0.0013 |
0.0001 |
0.0005 |
|
Pregnancy overall (%) |
87±4 |
73±5 |
52±6 |
76±10 |
83±9 |
57±9 |
NS |
0.0008 |
0.0002 |
NS |
|
Proportion lambing (%) |
73±4 |
62±5 |
36±6 |
63±11 |
76±10 |
44±10 |
NS |
0.0002 |
0.0004 |
NS |
|
Lambing rate (%)b |
89±6 |
75±7 |
28±8 |
71±14 |
85±13 |
56±12 |
NS |
0.0002 |
0.0002 |
0.0923 |
|
Age 1st lambing (days) |
418±1 |
421±1 |
427±2 |
424±3 |
421±3 |
419±3 |
NS |
NS |
NS |
0.0219 |
|
Number born |
1.3±0.04 |
1.2±0.05 |
0.9±0.07 |
1.1±0.11 |
1.3±0.10 |
1.2±0.11 |
NS |
NS |
NS |
0.0182 |
|
Puberty by breeding (%) |
32±3 |
42±4 |
-3±5 |
18±9 |
14±8 |
14±8 |
NS |
0.0004 |
0.0024 |
0.0014 |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Replicate 2:
Nutritional treatment, and progesterone pretreatment
The nutritional treatment increased estrous response but had no significant overall effects on fertility (Table 6). Reproductive response did not differ with progesterone pretreatment. There was no significant nutritional treatment X CIDR interactions for reproductive responses.
Breeding Weight Category
Breeding weight had no significant effects on fertility for replicate 2 (Table 7). There tended to be an increase in conception rate with heavier ewe lambs.
Average daily gain category
Animals that grew at faster rates had greater reproductive responses than the ewe lambs that experienced limited growth rates. This is evident by significant, pregnancy to first service and proportion of females lambing. There tended to be an effect for conception rate, overall pregnancy rate, and lambing rate.
Table 6 Effects of nutritional treatment (High v Low) and progesterone pretreatment
|
Reproductive Responses
|
Nutritional Treatment |
Progesterone Pretreatment |
||||
|
High |
Low |
p-value |
Yes |
No |
p-value |
|
|
Age at breeding (months) |
10.5±0.5 |
10.6±0.5 |
NS |
10.2±0.5 |
10.9±0.5 |
NS |
|
Weight at breeding (kg) |
42±2 |
40.2±0.8 |
0.0740 |
42.6±0.8 |
39.8±0.8 |
0.0110 |
|
Average daily gain (g) |
51±9 |
28±9 |
0.0936 |
49±9 |
30±9 |
NS |
|
Estrous response (%) |
100±5 |
77±7 |
0.0039 |
89±5 |
89±6 |
NS |
|
Conception rate (%) |
58±9 |
78±8 |
NS |
67±9 |
68±9 |
NS |
|
Pregnancy 1st service (%)a |
58±9 |
62±8 |
NS |
61±9 |
59±9 |
NS |
|
Pregnancy overall (%) |
45±9 |
62±8 |
NS |
52±8 |
55±9 |
NS |
|
Proportion lambing (%) |
44±9 |
52±10 |
NS |
43±9 |
52±10 |
NS |
|
Lambing rate (%)b |
47±10 |
56±11 |
NS |
50±11 |
52±11 |
NS |
|
Age 1st lambing (days) |
443±20 |
471±24 |
NS |
459±1 |
456±1 |
NS |
|
Number born |
1.1±0.1 |
1.1±0.1 |
NS |
1.16±0.09 |
0.99±0.08 |
NS |
|
Puberty by breeding (%) |
34±9 |
37±8 |
NS |
32±8 |
39±9 |
NS |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 7 Effects of breeding weight on reproductive responses in Dorset X females.
|
Reproductive Responses |
Breeding Weight Category |
|
||||
|
Heavy |
Medium |
Light |
H v M |
M v L |
H v L |
|
|
Estrous response (%) |
90±7 |
88±7 |
87±7 |
NS |
NS |
NS |
|
Conception rate (%) |
84±11 |
61±10 |
56±12 |
NS |
NS |
0.0970 |
|
Pregnancy 1st service (%)a |
76±11 |
53±10 |
51±11 |
NS |
NS |
NS |
|
Pregnancy overall (%) |
61±11 |
53±10 |
47±12 |
NS |
NS |
NS |
|
Proportion lambing (%) |
55±12 |
53±10 |
28±14 |
NS |
NS |
NS |
|
Lambing rate (%)b |
60±13 |
57±11 |
29±15 |
NS |
NS |
NS |
|
Age 1st lambing (days) |
458±2 |
458±1 |
455±3 |
NS |
NS |
NS |
|
Number born |
1.09±0.09 |
1.07±0.08 |
1.04±0.18 |
NS |
NS |
NS |
|
Puberty by breeding (%) |
38±11 |
30±10 |
39±11 |
NS |
NS |
NS |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 8 The reproductive responses of the average daily gain categories for experiment 2.
|
Reproductive Responses
|
Average Daily Gain Category |
|
||||
|
High |
Medium |
Low |
H v M |
M v L |
H v L |
|
|
Estrous response (%) |
88±7 |
92±7 |
83±8 |
NS |
NS |
NS |
|
Conception rate (%) |
67±10 |
78±10 |
49±12 |
NS |
0.0637 |
NS |
|
Pregnancy 1st service (%)a |
59±10 |
75±10 |
40±11 |
NS |
0.0231 |
NS |
|
Pregnancy overall (%) |
51±10 |
67±10 |
40±12 |
NS |
0.0815 |
NS |
|
Proportion lambing (%) |
49±10 |
62±11 |
24±13 |
NS |
0.0273 |
NS |
|
Lambing rate (%)b |
50±12 |
67±12 |
30±15 |
NS |
0.0596 |
NS |
|
Age 1st lambing (days) |
459±1 |
458±1 |
454±2 |
NS |
NS |
0.0761 |
|
Number born |
1.0±0.08 |
1.08±0.07 |
1.24±0.13 |
NS |
NS |
NS |
|
Puberty by breeding (%) |
29±10 |
40±10 |
37±11 |
NS |
NS |
NS |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 9 The reproductive responses of the weight day average categories for experiment 2.
|
Reproductive Responses
|
Weight Day Average Category |
|
||||
|
High |
Medium |
Low |
H v M |
M v L |
H v L |
|
|
Estrous response (%) |
95±5 |
86±8 |
85±7 |
NS |
NS |
NS |
|
Conception rate (%) |
81±9 |
48±11 |
52±10 |
0.0017 |
0.0271 |
0.0057 |
|
Pregnancy 1st service (%)a |
71±10 |
48±11 |
44±10 |
0.0795 |
NS |
NS |
|
Pregnancy overall (%) |
85±8 |
56±12 |
59±11 |
0.0031 |
0.0218 |
0.0053 |
|
Proportion lambing (%) |
68±11 |
35±9 |
39±10 |
0.0132 |
NS |
0.0577 |
|
Lambing rate (%)b |
74±13 |
41±15 |
39±10 |
0.0230 |
NS |
0.0561 |
|
Age 1st lambing (days) |
58±12 |
35±12 |
27±10 |
NS |
NS |
NS |
|
Number born |
1.08±0.23 |
1.17±0.13 |
0.99±0.41 |
NS |
NS |
NS |
|
Puberty by breeding (%) |
457±4 |
456±2 |
459±7 |
NS |
NS |
NS |
Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Pooled Replicate:
Nutritional treatment and progesterone pretreatment
Nutritional treatment had little effect on fertility with no difference observed for estrous response, pregnancy rates, proportion lambing and age at first lambing (Table 10). The high plane of nutrition group had a significant increase in prolificacy, and tended to have an increase the lambing rate.
A significantly higher amount of females that did not receive progesterone pretreatment were diagnosed pregnant to the first service, and tended to have a higher conception rate than ewe lambs that did receive a CIDR.
There tended (P=0.1050) to be a nutritional treatment X progesterone pretreatment interaction for overall pregnancy rates, and there was a significant interaction (P=0.0177) for nutritional treatment X progesterone pretreatment for puberty at breeding.
Breeding weight category
At the start of the experimentation period, there was no different in the percentage of ewe lambs that had initiated estrous cyclicity (Table 11). However, at breeding, the heavier females has a significantly higher proportion of ewe lambs having reached puberty compared to the medium and light weight breeding groups. The heavy and the medium breeding weight categories were significantly younger than the light breeding weight category.
Animals that were heavier at breeding had an increased fertility response. As breeding weight increased, estrous response, conception rate, pregnancy to first service, overall pregnancy rate, proportion lambing, and lambing rate increased respectively. Additionally, the heavy females had a significantly higher prolificacy compared to medium and light breeding weight ewe lambs.
Average daily gain category
Though there was no significant difference observed for estrous response, elevated levels of average daily gains during the treatment period significantly increased fertility by increasing the proportion that conceived, was diagnosed pregnant to the first service, and was pregnant overall. Additionally, an increased rate of liveweight gains in the pre-breeding period increased the proportion lambing, lambing rate, and prolificacy, but did not affect age at first lambing. Further, animals that averaged greater gains during this period tended to have a greater proportion undergo puberty prior to breeding. 12
Weight day average
Weight day average significantly impacts reproductive responses and overall fertility. Greater weight day average growth rates result in a successive increase in estrous response, conception rate, pregnancy outcomes, proportion lambing, lambing rate, and prolificacy. The animals that higher weight day averages were younger than the animals that grew at a slower rate. Additionally, an increased weight day average resulted in a significantly decreased age at first lambing compared to those that grew more slowly. 13
Average breeding weight, average daily gains, and weight day averages for positive and negative reproductive outcomes
Positive reproductive outcomes were associated with greater breeding weights, increased average daily gains, and elevated weight day averages (Table 14). Additionally, heavier breeding weights, average daily gains, and weight day averages were associated with the ewe lamb’s ability to support and successfully lamb multiple fetuses.
Table 10: Effects of nutritional treatment (High v Low), and progesterone pretreatment on reproductive responses on all Dorset X ewe lambs
|
Reproductive Responses
|
Nutritional Treatment |
Progesterone Pretreatment |
||||
|
High |
Low |
p-value |
Yes |
No |
p-value |
|
|
Age at breeding (months) |
9.3±0.2 |
9.2±0.2 |
NS |
9.2±0.2 |
9.5±0.2 |
0.0155 |
|
Weight at breeding (kg) |
45±1 |
43±1 |
NS |
42±1 |
46±1 |
0.0008 |
|
Average daily gain (g) |
94±6 |
65±6 |
0.0007 |
74±5 |
86±7 |
0.1364 |
|
Estrous response (%) |
77±3 |
75±3 |
NS |
74±3 |
81±5 |
NS |
|
Conception rate (%) |
76±4 |
79±4 |
NS |
74±3 |
84±5 |
0.0988 |
|
Pregnancy 1st service (%)a |
58±4 |
59±4 |
NS |
55±3 |
68±5 |
0.0319 |
|
Pregnancy overall (%) |
76±4 |
73±3 |
NS |
76±3 |
70±5 |
NS |
|
Proportion lambing (%) |
63±4 |
60±4 |
NS |
60±3 |
65±5 |
NS |
|
Lambing rate (%)b |
79±5 |
66±5 |
0.0802 |
71±5 |
75±7 |
NS |
|
Age 1st lambing (days) |
429±1 |
431±1 |
NS |
430±1 |
430±2 |
NS |
|
Number born |
1.3±0.04 |
1.1±0.04 |
0.0046 |
- |
- |
- |
|
Puberty by breeding (%) |
26±4 |
39±4 |
0.0206 |
21±3 |
43±5 |
0.0001 |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 11: Effect of breeding weights on reproductive responses in all Dorset X ewe lambs.
|
Reproductive Responses |
Breeding Weight Category |
|
||||
|
Heavy |
Medium |
Light |
H v M |
M v L |
H v L |
|
|
Estrous response (%) |
91±4 |
73±4 |
50±5 |
0.0005 |
0.0003 |
<0.0001 |
|
Conception rate (%) |
89±4 |
74±4 |
47±7 |
0.0108 |
0.0011 |
<0.0001 |
|
Pregnancy 1st service (%)a |
81±4 |
54±4 |
24±6 |
<0.0001 |
<0.0001 |
<0.0001 |
|
Pregnancy overall (%) |
85±4 |
75±4 |
49±5 |
0.0698 |
<0.0001 |
<0.0001 |
|
Proportion lambing (%) |
71±4 |
61±4 |
41±6 |
NS |
0.0091 |
0.0001 |
|
Lambing rate (%)b |
91±6 |
67±6 |
43±8 |
0.0067 |
0.0212 |
<0.0001 |
|
Age 1st lambing (days) |
427±1 |
429±1 |
441±2 |
NS |
<0.0001 |
<0.0001 |
|
Number born |
1.3±0.04 |
1.1±0.05 |
1.0±0.08 |
0.0048 |
NS |
0.0065 |
|
Puberty by breeding (%) |
41±4 |
23±4 |
13±5 |
0.0016 |
NS |
<0.0001 |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 12 Effect of average daily gain categories and total weight gained during the feeding period on reproductive responses in Dorset X ewe lambs.
|
Reproductive Responses |
Average Daily Gain Category |
|
||||
|
Heavy |
Medium |
Light |
H v M |
M v L |
H v L |
|
|
Estrous response (%) |
78±4 |
77±4 |
68±5 |
NS |
NS |
NS |
|
Conception rate (%) |
82±4 |
82±4 |
59±6 |
NS |
0.0032 |
0.0026 |
|
Pregnancy 1st service (%)a |
64±4 |
63±4 |
40±6 |
NS |
0.0024 |
0.0014 |
|
Pregnancy overall (%) |
80±4 |
74±4 |
64±6 |
NS |
NS |
0.0189 |
|
Proportion lambing (%) |
68±4 |
61±4 |
49±6 |
NS |
NS |
0.0131 |
|
Lambing rate (%)b |
86±6 |
66±6 |
58±9 |
0.0164 |
NS |
0.0078 |
|
Age 1st lambing (days) |
430±1 |
431±1 |
433±1 |
NS |
NS |
NS |
|
Number born |
1.3±0.04 |
1.1±0.048 |
1.2±0.08 |
0.0029 |
NS |
NS |
|
Puberty by breeding (%) |
31±4 |
29±4 |
19±6 |
NS |
NS |
0.0869 |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 13 Effect of weight day average category on reproductive responses in Dorset X ewe lambs.
|
Reproductive Responses |
Weight Day Average Category |
|
||||
|
Heavy |
Medium |
Light |
H v M |
M v L |
H v L |
|
|
Estrous response (%) |
92±4 |
81±4 |
43±5 |
0.0505 |
<0.0001 |
<0.0001 |
|
Conception rate (%) |
91±4 |
73±5 |
55±7 |
0.0044 |
0.0396 |
0.0001 |
|
Pregnancy 1st service (%)a |
81±4 |
60±5 |
23±6 |
0.0007 |
<0.0001 |
<0.0001 |
|
Pregnancy overall (%) |
87±4 |
74±4 |
53±5 |
0.0235 |
0.0028 |
<0.0001 |
|
Proportion lambing (%) |
75±4 |
63±5 |
38±6 |
0.0932 |
0.0012 |
<0.0001 |
|
Lambing rate (%)b |
92±6 |
79±7 |
32±8 |
NS |
<0.0001 |
<0.0001 |
|
Age 1st lambing (days) |
427±1 |
431±1 |
436±2 |
0.0480 |
0.0202 |
0.0002 |
|
Number born |
1.3±0.04 |
1.2±0.05 |
0.9±0.07 |
NS |
0.0004 |
<0.0001 |
|
Puberty by breeding (%) |
41±4 |
23±4 |
13±5 |
0.0016 |
NS |
<0.0001 |
- Number of ewes diagnosed pregnant on day 30-35 as a percentage of all ewes exposed to rams.
- Lambs born per ewe exposed to ram.
Values are least square means ± SEM (number of animals).
Table 14 Weight day averages, breeding weights, and average daily gains for animals experiencing positive reproductive outcomes.
|
|
Estrous response |
Conception Rate |
Pregnancy 1st service |
Pregnancy overall |
||||||||
|
Yes |
No |
P-Val |
Yes |
No |
P-Val |
Yes |
No |
P-Val |
Yes |
No |
P-Val |
|
|
Bred weight (kg) |
45±1 |
36±1 |
P<0.0001 |
47±1 |
40±1 |
P<0.0001 |
47±1 |
39±1 |
P<0.0001 |
45±1 |
39±1 |
P<0.0001 |
|
ADG (g) |
83±5 |
64±8 |
0.0344 |
91±5 |
58±9 |
0.0011 |
91±5 |
62±6 |
0.0003 |
87±4 |
54±8 |
0.0002 |
|
Weight day average (g) |
171±2 |
144±3 |
P<0.0001 |
174±2 |
151±3 |
P<0.0001 |
177±2 |
148±2 |
P<0.0001 |
170±2 |
149±3 |
P<0.0001 |
|
|
Proportion Lambing |
Lambing to 1st |
Prolificacy |
Puberty breeding |
|||||||||||
|
Yes |
No |
P-Val |
Yes |
No |
P-Val |
3 |
2 |
1 |
1v2 |
1v3 |
2v3 |
Yes |
No |
P-Val |
|
|
Bred weight (kg) |
45±1 |
40±1 |
P<0.0001 |
47±1 |
41±1 |
P<0.0001 |
61±5 |
51±1 |
44±1 |
P<0.0001 |
0.0016 |
0.0883 |
48±1 |
42±1 |
P<0.0001 |
|
ADG (g) |
91±5 |
64±6 |
0.0007 |
96±6 |
72±5 |
0.0025 |
169±44 |
114±12 |
85±5 |
0.0221 |
0.0613 |
0.2342 |
92±8 |
72±5 |
0.0261 |
|
Weight day average (g) |
172±2 |
155±3 |
P<0.0001 |
178±3 |
158±2 |
P<0.0001 |
227±18 |
189±5 |
167±2 |
P<0.0001 |
0.0008 |
0.0353 |
177± |
159±2 |
P<0.0001 |
Experiment 1:
Gonadotropic stimulation following progesterone pre-treatment can be used to improve reproductive outcome in fall-born ewe lambs bred during the mid-anestrous period with estrous response and pregnancy rate to the first service period comparable to that observed in adult females. Progesterone pre-treatment alone was sufficient to induce fertile estrus and advance the breeding season in yearlings bred during mid- and late-anestrus.
Experiment 2:
A single measure of concentration of AMH of replacement females may be a useful tool to select replacement females with a high reproductive performance. However, it is important to consider breed when developing threshold values to delineate the potential for high and low reproductive outcome as the concentration of AMH varies among breeds of sheep.
Experiment 3:
- Increased weight at breeding significantly impacts overall fertility in ewe lambs and this is consistent with current literature.
- There is some evidence that increasing the level of nutritional supplementation and increasing average daily gains in the immediate prebreeding period can impact fertility. However, a short term increase in supplementation may not be enough to overcome previous nutrient restrictions or light weight gains.
- Therefore, achieving higher gains over the animal’s lifetime rather than focusing on the prebreeding period may be a better management strategy than focusing on peri-breeding nutritional management
- Knowing specific breeding weights, average daily gains, and weight day averages for ewe lambs experiencing positive reproductive outcomes speaks to the economic benefits of efficient nutritional management to optimize reproductive performance in the first breeding season. Overfeeding and achieving a breeding weight that is substantially higher than the average is not economically beneficial. Fertility of animals that are bred at light breeding weight is low resulting in a missed opportunity to lamb by 1 year of age.
- Fertility in ewe lambs can be increased by managing nutritional supplementation and weight gains prior to puberty; however, the level of supplementation required and subsequent impact will vary with breed.
Education
This project combined a comprehensive educational program and on-farm trials on approaches to enhance the productivity of ewe lambs. Workshops created awareness of the problem including potential losses and gain feedback on planned project activities. Workshops on “Management Practices to Enhance Productivity of Replacement Ewe Lambs” were conducted. Farm visits will be made to collaborating producer operations to plan, discuss and implement off-farm trials and to complete recording templates. Producers attended field days held at collaborating producers where the project team, together with the producers discussed the research activities, results and benefits and where the use of CIDRs, ultrasonography, body condition scoring, and breeding soundness examinations were demonstrated. The combined educational and research project increased farmers knowledge and skills on reproductive management, selection and feeding practices to enhance replacement ewe lambs productivity and to assess the cost of rearing replacement ewe lambs
Topics covered included:
- Assessing productivity including pregnancy rates, lambing rates, total weight of lambs weaned
- Determining production cost of replacement ewe lambs and assessing profitability using breakeven analysis and partial budgets
- Factors influencing productivity of replacement ewe lambs (age, month of breeding, nutrition, genetics including economically relevant traits, breed)
- Selecting replacement females including use of individual performance and pedigree information, and visual observation
- Feeding replacement females including nutritional requirements, feeding to achieve desired weight gains and breeding weights and feeding the lactating replacement ewe lamb
- Reproductive management practices for increasing productivity of replacement ewe lambs including body condition scoring, breeding soundness examination, CIDR-based estrus synchronization protocols, pregnancy diagnosis and benefits of early pregnancy detection
Milestones
550 sheep producers in WV, PA, and MD learn about the replacement ewe program and receive an online and paper survey about their management practices.
550
500
August 31, 2014
Completed
August 31, 2014
Producers were contacted and sent information, follow up phone calls made, surveys completed and information collated and analysed.
150 producers return the survey and 100 agree to participate in the education program and 25 agree to host on farm trials and demonstrations.
25
15
September 30, 2014
Completed
October 07, 2014
80 producers attend workshop and become familiar with the project performance target, estimating cost of rearing replacements and, management strategies to enhance reproductive performance.
80
75
1
March 31, 2015
Completed
March 31, 2015
Three (3) meeting conducted where producers are informed of project. This was supplemented with over 25 field visits to further discuss the project.
8-10 producers initiate on-farm trials with support of project team.
8
5
November 30, 2014
Completed
September 01, 2015
817 replacement females ranging in age from 6.5-16 months from 5 farms were used to evaluate the effects of age, progesterone, nutrition supplementation and gonadotropin stimulation on fertility of ewe lambs.
50 producers attend on-farm trials and learn about CIDR devices, body condition scoring (BCS), breeding soundness exams (BSE), selection of replacement females and pregnancy diagnosis and life-cycle feeding strategies.
50
20
March 31, 2015
Completed
March 31, 2016
We used a combination of workshops, on farm visits with demonstrations to surrounding farmers to accomplish this milestone.
10 cooperating farmers submit production records.
10
4
May 31, 2015
Completed
June 01, 2016
We collected data throughout the trials and collected and verified all lambing data from producers. This was done by producers submitting lambing data electronically as well as farm visits during the lambing period to ensure appropriate records were collected and to address discrepancies in data submitted electronically.
100 producers attend workshop and discuss results of initial trials, 15 additional cooperating procedures are selected for farm trials and 60 additional producers agree to implement management practices and receive production records templates.
100
120
August 31, 2015
Completed
October 14, 2016
Data from the first replicate was collated and presented to farmers and presented at scientific meetings. These presentations were made as components of larger workshops including Women in Agriculture Conference and annual producer meetings. Additionally field visits were used to discuss the individual results with participating producers.
10-15 new producers initiate on-farm trials, 70 additional producers implement replacement ewe management practices.
10
8
November 30, 2015
Completed
October 31, 2016
We were able to generate significant interest in the program. Many farmers expressed interest in implementing the management practice but did not want to be in the actual research project. This was due to time commitments, the need to individually identify their animals and the recording and reporting requirements. We were able to get an additional 4 producers to start in the second round of trials and another 4 producers to implement the practice. In total over 1500 ewe lambs were added to the project.
50 producers provide feedback, receive management team support to implement management practices and complete management records.
50
22
December 31, 2015
Completed
March 30, 2018
As a result of the project we were frequently asked to participate in a number of activities , including on farm where we demonstrated pregnancy diagnosis, breeding soundness examinations, selection of replacement females, use of CIDRs and discussed appropriate records that should be maintained. These areas were also discussed at various producer meetings.
60 producers submit production records.
60
15
May 31, 2016
Completed
June 01, 2017
While several farmers participated in implementing management practices fewer were interested in being a formal part of the project and even less kept the required records. Therefore less than 25% of the projected number of producers submitted records for analysis. This data was compiled and analyzed and was sufficient for drawing conclusions and publication.
60 producers document number of ewe lambs receiving new management practices and changes in productivity and revenue by submitting completed verification information to project team. 100 producers attend workshop and discuss results of trials.
60
65
September 30, 2016
Completed
October 01, 2017
At least 15 producers have adopted the full suite of management practices recommended and another 50-60 producers attempt to breed replacement females at ewe lambs. Some provide additional nutritional supplementation while others simply turn the rams in with the ewe lambs. This represents a significant change in management of replacement females. Most producers of the 60 producers we routinely engage with have adopted or will be attempting this management practice in the future.
Milestone Activities and Participation Summary
Educational activities:
Participation Summary:
Learning Outcomes
The major verifiable area of change was increase willingness to breed replacement females at a younger age. This was verified by increase interest to get involved in the trials or guidance on getting ewe lambs bred. Also cooperating farmers increased the number of replacement females they assigned to the management protocols. Other areas of change: Increase use of progesterone pre-treatment to synchronize and induce estrus in ewe lambs, increase use of pregnancy diagnosis to confirm pregnancy and to identify non-pregnant animals that can be culled, Increase use of grain supplements in feeding ewe lambs, increase interest and practice of weighing and monitoring weight changes in animals, interest in purchasing animals with genetic values for traits of interest.
Performance Target Outcomes
Target #1
50
Manage 4500 ewe lambs to be bred for the first time at 7-9 months of age using a combination of improved nutritional management and progesterone pre-treatment.
Observed improvements in lambing rate varied from 13 to 50% across various treatment categories. Assuming an average improvement of 30% this will equate to 1350 more lambs
1350 more lambs produced annually valued at $270,000
Target #2
Adoption of various practices was verified primarily through field visits and one on one discussions.
- Increase interest and adoption of breeding ewe lambs was verified by increases in the number of producers requesting assistance for implementing the strategy, increasing number of producers actually implementing the strategy, increase in the number of ewe lambs participating producers used in implementing the strategy and phone survey of producers.
- Increase interest and use of pre-breeding feeding programs and phone survey of producers willingness to implement feeding strategies.
- Increase use of pregnancy diagnosis; Verified by increase request for conducting pregnancy diagnosis and the number of animals we conducted this procedure on.
- Increase interest and use of purchasing replacement females with breeding values; Verified by interest in sour ces of such animals and increase sales form producer with animals with known EBVs
Additional Project Outcomes
From a medium-sized sheep producer in Pennsylvania. "I was not sure that breeding ewe lambs to lamb at 1 year of age would work. it is just something I never did. So I was pretty sure breeding ewe lambs to during the spring and summer would not work. To my surprise it did. I now know that using the right nutrition and reproduction strategies can make breeding ewe lambs possible"
Information Products
- Effect of stimulation with a gonadotropin mixture onreproductive outcome in nulliparous ewes bred duringseasonal anestrus and early breeding season
- The Relationship between the Concentration of Anti-Mullerian Hormone (AMH) and Fertility in Replacement Females
- LIFETIME PRODUCTIVITY OF THE EWE FLOCK STARTS WITH THE EWE LAMB