Enhancing the productivity of ewe lambs through the use of reproductive management

Enhancing the productivity of ewe lambs through the use of reproductive management

Summary

Replacement ewe lambs comprise 30% of the breeding flock but their productivity is 30-40% lower than that of adult ewes resulting in significant loss in revenue. Delaying breeding of females until they are 15-18 months increases cost of production and does not consistently improve performance.

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.

Objectives/Performance Targets

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.

Accomplishments/Milestones

Research Component

1. In the second phase of our study we used 455 replacement females ranging in age from 4-10 months to evaluate the effects of age, progesterone, and nutrition supplementation on the fertility of ewe lambs bred during the breeding season. Our preliminary findings suggest the following: a. Progesterone pretreatment improves the conception rate by 22% and the proportion of ewe lambs lambing and the lambing rate by 10 (50 vs 59.6) and 17 (50 vs 67.3) percentage points b. Increasing the plane of nutrition 2 months prior to breeding resulted in a doubling of the weight gain of ewe lambs and increased conception rate by 16% but only increased lambing rates by 8.3 %

2. Replacement ewes bred at 6-7 months showed lower lambing rates (55%) than those bred at 7-8 (69%) and 8-12 (71%) months. Lambing rate to the first service period and prolificacy was higher in ewe lambs bred at 8-12 months of age (51 and 120%) than at younger ages (30 and 100 %). Overall lambing rates was not different among replacements bred between 7-8 and 8-12 months.

3. Blood samples from 437 replacement females have been analyzed to determine circulating concentrations of anti-Mullerian hormone (AMH). Mean AMH concentration in ewe lambs was 472 pg/ml and varied with breed (416 and 592 pg/ml for wool and Katahdin breeds respectively; breed was confounded with farm). Our preliminary findings suggest that concentration of AMH is not a reliable marker of fertility in ewe lambs
 

4. A third replicate using another 175 ewe lambs was initiated in September.
 

Educational Component

1. Four educational meetings (one in Pennsylvania and three in West Virginia) were conducted where the benefits of improving the fertility of replacement females were discussed and initial findings were presented to a total of 133 producers.

2. A manual on raising replacement females is being prepared

3. Four educational meetings are planned for spring 2017 including one in Delaware, January 10^th 2017.

4. Preliminary findings were published as an abstract and presented at a major conference: Redhead, A.K., Adebiyi, A.E., Paul, C.D., Keller, E.N., Powell, K.J. and Knights, M. The effect of age, plane of nutrition, and progesterone pretreatment on lambing rate in nulliparous females bred during the breeding season. Midwestern Section of ASAS and Midwest Branch ADSA, Des Moines, Iowa, USA. March 14-16, 2016. J. Anim. Sci. 94: (supp. 2): 27-27 doi:10.2527/msasas2016-059

Table 1: Effect of Age of breeding, progesterone pre-treatment and nutrition supplementation on reproductive outcome in ewe lambs¹.

¹ Ewe lambs between 4-10 months of age were provided with a daily grain supplement (0.2 or 0.7 kg/d) for 60 days prior to the breeding.  Half of the ewe lambs in each supplementation group were pretreated with progesterone for 5 days prior to ram introduction using a CIDR-g device (0.3 g progesterone).

Impacts and Contributions/Outcomes

Our direct efforts from the studies conducted on this project in 2015/2016 resulted in lower ewe lamb replacement costs and produced 250 additional lambs on four farms valued at more than $50,000. Additionally, our training and workshops are projected to change management practices of an additional 50 more producers who will breed at additional 2500 ewe lambs and derive 1200 additional lambs each year.

We also demonstrated that progesterone pretreatment can be beneficial in assisting ewe lambs to be bred as early as 8 months without compromising fertility. Implementation of early breeding of ewe lambs will reduce the cost of raising replacements by 33-50%.

Two graduate students (one PhD, one MSc.) are projected to complete their research on studies in this project and graduate in 2017

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Collaborators: