Final Report for GW08-001
The impact of partially substituting bluegrass straw (BGS) for alfalfa hay to reduce N and P intake in early lactation cows was determined. Cows were fed a control ration or a ration in which 10% of alfalfa hay was replaced by BGS. Feed intakes were higher for the BGS ration whereas in vitro digestibility, feed costs, income-over feed cost, fecal P and N, and feeding behavior were unaffected. Milk yield and income was reduced but not income-over-feed costs. Thus, BGS in diets of lactating cows reduced the %P and %N, N intake, and aided nutrient management.
The greatly accelerated production of ethanol in the U.S. increased prices of feed grains but also increased the availability of distillers grains & solubles (DGS) for livestock feeds. Because DGS contains comparatively high fiber content, most DGS is fed to cattle. The high phosphorus (P) and crude protein (CP) content of DGS challenges existing nutrient management plans for dairy farms, most of which already have excess P imports and face increased scrutiny concerning ammonia emissions. Feed ingredients containing low concentrations of P and N need to be included in rations to offset the high P and N in the DGS. Recently, bluegrass straw (BGS) was added to diets of cows entering their final 100 days of lactation without affecting milk yield or composition (O’Rourke et al., 2007). In addition, incorporating BGS into diets instead of field burning the bluegrass seed residue reduces particulate emissions, which can reach 159 kg PM2.5 per acre (Johnston and Golob, 2004).
Environmental stewartship involves developing and adopting sustainable agricultural practices that must be economicaly viable. Currently, a challenge to environmental stewardship is incorporating the available DGS from ethanol production into livestock diets without overloading soils with P from livestock manure, thus significantly increasing P in surface water and increasing ammonia emissions from dairies. When corn grain is used for ethanol production, approximately 1 kg of dried DGS is produced from 3 kg of corn, thus as ethanol production and the availability of DGS increase, the availability of corn as a feed grain decreases. Because DGS contains more than 0.65% P and nearly 30% CP (Stein et al., 2006), replacing 5 kg of corn with DGS increases the concentration of CP in lactation diets by 4% units and P by 0.08% units. Accordingly, a basal diet that contained 16% CP and 0.4% P contains 20% CP and 0.48% P when DGS is substituted for about half of the corn. These dietary levels of CP and P (20% and 0.48%, respectively) are unacceptably high from the standpoint of P loads and ammonia emissions.
Perhaps the best way to lessen the impact of dietary DGS on N and P excretion of cattle is to increase use of feed ingredients that contain low CP and P concentrations. For example, BGS contains only 8% CP and 0.19% P. O’Rourke (2007) found when BGS partially replaced alfalfa hay, the %CP in the lactation diet was reduced from 18.9% CP in the Control diet to 17.8% in the diet with 10% BGS, and 17.5% CP in the diet with 15% BGS. This equates to a daily reduction of 57 g of N/cow/day or an annual reduction of over 20 kg of N/cow/year. Dairy cattle producing 41 kg of milk/day and fed diets with 19% CP excrete about 0.5 kg N/cow/day (Nennich et al., 2005), emit about 170 kg of ammonia/cow/year (Rumburg et al., 2004), of which 55 kg of ammonia is lost via an open anaerobic dairy waste lagoon (Rumburg et al., 2008). Reducing N intakes of cows is the most effective way to reduce N excretion and ammonia emissions. Similarly, the low concentration of P in BGS can be used to offset the high concentration of P in DGS (Lemenager et al., 2006).
O’Rourke (2007) found feeding 10% BGS as a partial replacement for alfalfa hay reduced daily feed costs by about $27/day for 100 cows or nearly $10,000 per year for 100 cows. In addition to reducing feed costs for dairies, use of BGS in lactation diets gives bluegrass seed growers an additional market for their bluegrass straw and reduces particulate emissions from field burning. In the Pacific Northwest there are about 152,000 acres of Kentucky bluegrass grown (Holman and Thill, 2005). Total emissions from burning the residue on bluegrass fields are estimated at 13.6 to 56 kg of PM2.5 per acre in eastern Washington to 159 kg of PM 2.5 per acre in northern Idaho (Johnston and Golob, 2004).
The results of a previous Western SARE Graduate Student Fellow Grant (O’Rourke et al., 2007) with using BGS in lactation diets were: 1) bluegrass straw can be added at levels up to 15% (in replacement of alfalfa hay) of diets fed to lactating cows in late lactation (219 days-in-milk at the start of the study) without affecting milk yield or milk composition; 2) partial replacement of alfalfa hay with bluegrass straw reduced the %CP in diets, thus reducing N excretion; and 3) partial replacement of alfalfa hay with bluegrass straw reduced feed cost without adversely affecting milk yield or composition. Likewise, in the previous study (O’Rourke et al., 2007), partial replacement of alfalfa hay with bluegrass straw had a larger effect of reducing N excretion than P excretion because the difference in CP between BGS and alfalfa hay is much larger than the difference in P between BGS and alalfa hay. Because the results of the previous study showed BGS can be added to diets of lactating cows without affecting milk production, there is justification to expand the use of BGS in dairy diets. This proposal extends previous work of feeding BGS to late lactation cows and proposes to use BGS to reduce N and P excretion of cows in mid-lactation fed diets contains DGS. The proposed study also considers income over fee costs. Thus, the hpothesis is that BGS in diets will reduce N and P excretion in early to mid-lactation cows fed DGS and improve net income of dairies.
- The objectives are to determine if:
1. bluegrass straw can be used in diets to offset the increased excretion of nitrogen and phosphorus of cattle fed distillers grains & solubles;
2. bluegrass straw can be fed to cows in early to mid-lactation without affecting milk yield and composition; and
3. income over feed costs is affected when bluegrass straw is incoporated into lactation diets.
SUBJECTS, HOUSING AND EXPERIMENTAL DESIGN
Two pen groups of 60 Holstein cows were housed in freestall barns with headlock gates in the feed alleyways. Pen 1 contained 75 headlock gates, 80 freestalls and had a bunk length of 45m; Pen 2 contained 66 headlock gates, 56 freestalls and had a bunk length of 40m. Thus, there was 0.75m and 0.67m of feed bunk space per cows in Pens 1 and 2, respectively. Headlock gates provided approximately 0.6m of space per gate. Pens were floored entirely in concrete and the freestalls were bedded with sawdust. Feed was delivered on the concrete floor in the alley in front of the headlock gates. Two subsets of 12 cows in early to mid lactation were selected based on days in milk (DIM) and milk yield from within the two larger pen groups for data collection. Selected cows were between 60 and 200 DIM with an average of 114 DIM. Cows were paired between the two pens based on milk yield so that each subset of 12 cows contained a similar range of milk production. All cows within a pen were assigned either a control TMR or a TMR containing 10% BGS (dry matter basis). Cows were fed once per day at 0800 h and milked twice per day at 0900 and 2100 h. Each morning, cows were locked in the headlock gates prior to daily delivery of fresh feed and headlock gates were released 30 to 40 min post feed delivery. This was to allow for cleaning of the pens and herd management. Feed was pushed up periodically throughout the day, and 24 h refusals were scraped from the feed alley 30 min prior to daily delivery of fresh feed. Cows were fed ad libitum and pen groups were fed for approximately 10% refusals.
The ingredient composition of the diets is listed in Table 1. Control and BGS diets were mixed immediately prior to feeding. The BGS was chopped in a tub grinder prior to being added to the feed mixer truck. Cows within each pen were fed their respective diet for 3 weeks (Period 1). The diets were then switched between pens and cows were fed the alternate diet for an additional 3 weeks (Period 2). Cows in Pen 1 received the control diet in Period 1 followed by the BGS diet in Period 2,whereas the reverse was true for the cows in Pen 2. Daily feed intake data were collected for the entire pen. Behavioral, fecal, milk and serum data were collected from the subset of 24 focal cows. In wk 3, one cow suffered from an injured teat and was totally removed from the study. In wk 6, one cow was diagnosed with pneumonia and data from this cow were removed from Period 2.
Feeding behavior was observed on d 1, 8, 15, 22, 29 and 36. On observation days, the cows were
not handled outside the normal feeding and milking routine. Cows were observed twice per day
for 30 min immediately following delivery of fresh feed at approximately 0800 h and again for
30 min between 1600 and 1700 h. Cows were marked with grease-pens for ease of identification
during observation. The cow’s ID number was written in large numbers on each side of the
rump, and a unique mark was placed on the face directly between the eyes for identification in
the headlock gates. Each treatment group was observed separately. Because a different TMR was mixed for each pen, there was a 30 to 45 min time difference in time of feed delivery to each pen. Morning observation began immediately following delivery of fresh feed, so the pen fed first was observed first. The control diet was always fed first, and the BGS diet fed second throughout the study. During the entire observation period, cows were locked in headlock gates. The afternoon observation period occurred when there ws relatively little physical activity at the dairy. Cows were not locked up and were able to move freely about the pen. The pen receiving the control diet was also observed first in the afternoon observation sessions. Behavior was recorded every minute in an instantaneous scan sample. Behaviors were defined as follows: (1) Present at feed bunk: Cows’s ears are through the headlock gate; (2) Chewing: Cow is present at feed bunk, head at any height, jaws are moving rhythmically in chewing motion. Intra-observer concordance was established by making 10 min videos of each group of cows at the feed bunk on three occasions one month prior to the start of the study. The observer collected behavioral data twice independently from each video. On average, there was 97% concordance between the two sets of data from each video.
Feed and Fecal Sample Collection
Fresh TMR was sampled each day immediately after fresh TMR delivery to each pen. Grab samples (~150 g) of TMR were obtained at 1 m intervals along the feed alley and combined. Orts were collected in 150 g grab samples from random places in the ort pile after they were removed from the feed alley. Particle size separation was performed on 200 g subsamples of fresh TMR and orts, after which the remainder of the sample was frozen for further analysis. Daily feed intake and feed cost data were collected for each pen using the TMR Tracker Lite ™ computer program.
Fecal samples were obtained by rectal grab sampling on d 2, 16 and 37. Between 100 and 200g
of wet feces were collected from each focal cow using a disposable OB glove and brought back
to the lab for analysis. Samples were collected between 0800 and 0900 h on sampling days.
Blood and Milk Sample Collection
On d 2, 16 and 37, blood was collected from the coccygeal vein of each focal cow and allowed to
clot in the collection tube. Samples were placed on ice and taken back to the lab for serum
extraction and analysis. Milk was collected on d 2, 9, 16, 23, 30 and 37. Samples from both morning and night milking within cow were combined. A milk subsample for each cow was preserved with bronopol and sent to the Washington State Dairy Herd Information testing laboratory for analysis of milk fat, protein, lactose, somatic cell count, and solids-not-fat. A second subsample was untreated and frozen until analysis for milk urea nitrogen (MUN) was performed. Daily milk yield data were collected for the subset of 24 cows.
Data for morning and afternoon observations were analyzed separately because the cows were locked up in the headlock gates in the morning whereas in the afternoon they were free to choose their activity. For both sessions, the proportion of scans in which each cow was observed to be chewing while present at the feed bunk was calculated. For afternoon sessions, the proportion of scans in which each cow was at the feed bunk out of total scans was also calculated.
Particle size separation of both fresh TMR and orts was determined using a Penn State Particle
Separator (Lammers et al., 1996). Two hundred grams of feed was weighed and placed in the top
separator screen. The separator was then shaken back and forth 4 times in each direction for a
total of 16 times. The contents of each screen were weighed and recorded.
Feed and fecal samples were dried in a 60°C oven for 48 h to determine DM (AOAC, 2005). Once dry, samples were ground through a 2-mm screen in a Wiley mill (Arthur H. Thomas and Co., Philadelphia, PA).Total DM was determined by drying a subsample of the ground sample
in a 100°C oven for 24 h. Feed and fecal samples were analyzed in duplicate for ash, crude
protein (CP; AOAC, 2005), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid
detergent lignin (ADL), and P (AOAC, 2005).
Crude protein was determined using a Leco FP-528 Nitrogen Analyzer (Leco Corporation, St.
Joseph, MI; AOAC, 2005). The N concentration of the sample was converted to CP concentration by multiplying N by 6.25. Neutral detergent fiber and ADF were determined using an Ankom Fiber Analyzer (Ankom Technology, Macedon, NY; AOAC, 1995). Fiber bags were analyzed for NDF, weighed back and then analyzed for ADF. Post ADF analysis, samples were analyzed for lignin using the protocol for acid detergent lignin (ADL) from Ankom Technology (Ankom, 2005). Sample bags
were submerged in 72% H2SO4 for 3 h and then rinsed with distilled water until pH > 6.0.
Samples were soaked in acetone for 5 min and then removed from acetone and allowed to dry.
After all the acetone had evaporated, samples were dried for 2 h. After ashing (AOAC, 2005) samples were assayed for P. Samples were boiled in 5 mL of 3N HCl for 10 min and then diluted to 50 mL in distilled water. Prior to P analysis, samples were diluted 1 to 4 in deionized water. Phosphorus was measured using a colorimetricc assay in a 96 well plate with 25 uL of sample and 100 uL of vandomolybdate reagent added to each well. Concentrations of ADL, P and N in the TMR and feces were used to estimate nutrient digestibility. Acid detergent lignin was used as a marker. Phosphorus and N digestibility was
calculated using the equation:
Digestibility = (% marker in feed / % marker in feces) * (% nutrient in feces / % nutrient in feed)
Total in vitro digestibility (IVTD) was determined on feed samples using an Ankom DaisyTMIncubator (Ankom Technology, Macedon, NY, USA). A composite sample of each diet was
obtained by combining a 100g subsample of each week’s ground fresh feed samples. Composite
samples were divided among fiber bags and placed in glass jars containing 1600mL of buffer
solution (pH 6.8) pre-warmed to 39°C. Ruminal inoculum was obtained from fistulated Angus
beef cows housed at the WSU Beef Center and fed a 100% BGS diet (Mabjeesh et al., 2000).
Blood was allowed to clot for approximately 2 h and then centrifuged at 2000 x g for 20 min to
obtain serum. Serum was transferred to microcentrifuge tubes and stored in a freezer at -20°C. Blood was thawed at 4°C prior to assay for P, non-esterified fatty acids (NEFA) and blood urea nitrogen (BUN). Serum was deproteinated using a 4:1 ratio of serum to 10% TCA prior to P assay. Serum P concentration was determined using a colorimetric assay (AOAC, 2001). BUN was determined using BioAssay Systems QuantiChrom Urea assay kit (DIUR-500). Serum
NEFA was determined using a WAKO HR series NEFA-HR(2) kit (Wako Diagnostics,Richmond, VA).
Milk samples were analyzed for fat, protein, lactose, somatic cell count and solids not fat. Fat corrected milk (FCM) was calculated using the equation:
FCM = 0.432 * milk yield (kg) + 16.32 * milk fat (kg; Brog, 1971).
4% energy corrected milk (ECM) was calculated using the equation:
ECM = [(383 * % fat + 242 * % protein + 163.2 * % lactose)/3140] * milk yield (kg; Sjaunja et
Milk was deproteinated using a 2:1 ratio of milk to 10% TCA prior to MUN analysis using the
BioAssay Systems QuantiChrom Urea assay kit (DIUR-500). One milliliter of milk was
combined with 0.5mL of 10% TCA and centrifuged at 14,000 rpm for 5 min. Supernatant was
transferred to a clean microcentrifuge tube and stored at 4°C. Five microliters of supernatant and 200uL of reagent were pipetted into a 96-well plate and read at 520nm for urea content.
The behavioral data were not normally distributed. Data were analyzed both untransformed andranked, and similarity between results for both analyses indicated reliability of the ranked data analysis (Zar, 1999). Only results from analysis of the ranked data are presented. Changes in proportion of time spent present at the feed bunk (afternoon only), proportion of time spent chewing at the feed bunk (morning and afternoon) for each period, and the effect of order of presenting the two diets to each pen were assessed using PROC MIXED of SAS (v. 9.1; SAS Institute Inc., Cary, NC). The model included pen, time, and pen by time. Cows were the subjects, time in weeks was a repeated measure, and an unstructured covariance structure was used. Mean comparisons were performed on least squared means with Tukey’s adjustment for multiple comparisons. No effects of week were found and, therefore, the PROC MIXED analysis was re-run after pooling the data for each 3-wk period. Using pooled data for each cow in each period, Wilcoxon matched pairs tests were performed to compare the difference in the number of scans that each focal cow was present at the feed bunk (afternoon only), and proportion of scans in which each cow was chewing while at the feed bunk (morning and afternoon), when fed the control vs. BGS diet. Because BGS was a novel feed ingredient for the cows, Wilcoxon matched pairs tests were also performed to assess differences in chewing frequency during the first and third week that the cows received each diet.
Statistical analysis on feed, feces, serum, and milk data was performed using PROC GLM of
SAS (v. 9.1; SAS Institute Inc., Cary, NC). Serum measurements, fecal data, and milk data from cows were analyzed for the effects of treatment, period and treatment by period interaction usinginitial values as a covariate to eliminate cow effect. The linear model was:
Yijk = u + Di + Pj + DPij + Covijk + Eijk
Yijk = the response of the kth cow in the ith diet and jth period and covijk was the initial valueFeed intake, feed costs, income and income over feed cost data were analyzed for the effects of treatment and period. The linear model was: Yijk = u + Di + Pj + DPij + Eijk
Yijk = the response of the kth observation in the ith diet and jth period
Total in vitro digestibility was analyzed for effects of sample and run. The linear model was:
Yijk = u + Si + Rj + SRij + Eijk
Yijk = the response of the kth observation in the ith sample type and jth run.
Bluegrass straw was much lower than alfalfa hay in CP (22.4 vs 6.9%), P (0.33 vs 0.11%) and higher in NDF (39.8 vs 73.7%). Therefore, partial replacement of alfalfa hay with 10% BGS reeuced dietary P by 8% and the CP concentration decreased by 8%. The comparatively high fiber content of the BGS did not affect the NDF and ADF concentration in the BGS diet cmpared to the control diet. ADL was also unaffected by inclusion of BGS in the diet. Total in vitro digestibility, as measured using the Dairy Incubator, was not affected by inclusion of BGS in the diet. Although BGS is less digestible than alfalfa hay, the relatively low inclusion rate of BGS and similar ADF and ADL content of the diets did not yield a significant difference i in vitro digestibility. Microbial protein production, as predicted using the CPM-Dairy mdoel, was reduced by 200g/d (from 4119 to 3911 g/d) by addition of BGS to the diet. Metaboliszable protein content of the diet was reduced by 78 g/d (from 1545 to 1467 g/d) in the BGS diet. Although overall DMI was higher for BGS fed cows, weekly DMI was only affected by inclusion of BGS during wk 4 and 6. During these weeks, DMI actually decreased in BGS fed cows. During wk 4 there was an increase in ambient temperature that could have contributed to the reduction in DMI in BGS fed cows. More heat is produced in the rumen from fermentation of fiber than from concentrates (Fuquay, 1981) and, because the BGS diet was higher in %NDF, it is possible that cows consumed less of the diet to compensate for heat production in the rumen. The decrease in milk production during wk 4 and 6 corresponds with the decrease in DMI.
Inclusion of BGS in the diet had no effect on the proportion of scans that cows spent chewing out of total scans at the feed bunk for both morning and afternoon observation sessions. Total chewing events for period 1 did not differ from total chewing events in period 2 regardless of which dietary tretment was provided first. In cows fed BGS in period 1, there was no difference in morning feeding behavior between wk 1, when the BGS diet was novel, and wk 3. However, in cows fed BGS during period 2, there was a difference in chewing frequency during the morning observation session in the first and third week of receiving the BGS diet. Inclusion of BGS in the diet had no effect on proportion of scans spent present at the feeder out of total scans for afternoon observation sessions. Overall proportion of scans in which chewing was recorded out of the total scans when cows were present at the feed bunk was not affected by inclusion of BGS in the diet. Time spent chewing was approximated by 1-0 scan sampling at 1-min intervals for each 30-min observation session. The exact number of chews performed during the observation period was not recorded due to the difficulty in simultaneously observing all 12 cows within each pen group of 60 cows. Although overall frequency of chewing was not affected by addition of BGS, cows fed BGS during period 2 were observed chewing less frequently on their first day of receiving the BGS than in the last week of receiving this diet. This finding could explain the lower DMI and milk yield for BGS fed cows during wk 4. Although cows may have initially found the BGS diet less palatable than the control diet in both periods, they may have decreased their intake of BGS in period 2 because of the heat wave.
Particle size distribution was affected by the partial replacement of alfalfa hay with BGS in the TMR. Inclusion of chopped BGS increased the long particle (>19 mm) fraction of the diet and decreased the percentage of particle between 8 and 1.18 mm in length. Sorting of the TMR by cows occurred for both the control and BGS diets. Orts of the BGS diet had a higher percentage of long particles than control orts, and a lower percentage of particles 8 to 19 mm. However, the percentages of long particles in the orts of both TMRs increase by about 27 percentage points, thereby indicating similar amounts of sorting against the long particles. Sorting of the TMR by cows is influenced by dietary forage content, chop length of forage, moisture content of the diet and forage quality. Cows sort for the concentrate portion of the diet and discriminate against long fibers. Leonardi and Armentano (2003) reported that feed sorting increased as the chop length of the forage increased. These researchers also found that increasing the quality of the alfalfa (from 44.5% to 34.5% NDF) in the TMR did not affect the feed sorting behavior of cows (Leonardi and Armentano, 2003). In the current study, although the long fiber portion of the diet was increased by the addition of BGS, sorting was unaffected. This could be because the increase in long fibers was not sufficient to cause an increase in feed sorting. Cows were fed for approximately 10% refusal rate, meaning they did not have to
consume all of the long particles of the diet before being supplied with fresh feed. Dairy cows
are typically fed for a refusal rate of 5% or greater to avoid empty feed bunks and allow access to feed at all times. If the refusal rate was lowered to less than 5% on the current study, less feed sorting, a greater intake of BGS, and consequently a reduction in fecal N and P concentration,might have been seen.
Cows sorted their feed regardless of dietary treatment, and the fraction of the diet sorted against(the long fraction) contained the lowest %P and CP of the diet components. Inclusion of BGS
increased the long particle (>19.0 mm) fraction of the diet. Both control and BGS diets had more
long particles than recommended (Heinrichs and Kononoff, 2002). Orts from the BGS diet had a
higher percentage of long particles than control, which could indicate greater sorting in cows fed BGS. However, when the percentage of long particles in the orts was compared to the percentage of long particles in the fresh TMR, the long particle fraction increased the same number of percentage points for both diets. The BGS orts contained a higher proportion of long particles than control orts because the BGS diet started out with a higher portion of long particles, indicating that degree of feed sorting was not increased by addition of BGS.
When the length of the forage is longer, cows increasingly discriminate against the long particles in the diet (Leonardi and Armentano, 2003). Although inclusion of BGS did not lead to increased feed sorting, reducing the chop length of the BGS could be a method used to encourage the cows to consume more of the BGS in the diet. However, chop length of BGS should be no less than two inches, as any finer chop than that results in increased ruminal passage and decrease of physically effective fiber (Yang and Beauchemin, 2007).
Phosphorus Intake and Fecal Excretion
Although % dietary P was reduced by inclusion of BGS, estimated P intake between treatment
groups was not affected. Dry matter intake increased in cows fed BGS, which resulted in similar P intakes. Because there was no difference in P intake, fecal excretion of P was not affected by addition of BGS. Serum inorganic P was unaffected by inclusion of BGS, indicating no change in the amount of P absorbed with similar amounts of P intake. Because fecal P excretion is highly correlated to P intake, similar P intakes resulted in similar levels of fecal P excretion regardless of dietary treatment. Ekelund et al. (2005) reported 23% reduced fecal P excretion when dietary P was reduced from 0.49 to 0.40%. Valk et al. (2002) found that a 34% drop in fecal P occurred when P intake was reduced from 0.33 to 0.28% P DM in cows with similar milk yields. Because there was no treatment effect on P intake, milk P secretion and fecal P excretion, overall P balance was unaffected by inclusion of BGS in the diet. Although BGS is a low P feed, the increase in total feed intake offset the lower % P such that BGS addition to the diet did not affect fecal excretion of P into the environment.
Nitrogen Intake and Fecal Excretion
Estimated daily N intake was reduced by the addition of BGS (P<0.05). However, calculated N
digestibility of the TMR was reduced by inclusion of BGS (P<0.05). This could be caused by reduced milk production in BGS fed cows, leading to less N leaving in the milk which would
show up as a decrease in apparent N absorption. Because BGS has less readily fermentable
carbohydrate for microbial protein production and a greater proportion of longer particles than
the control diet, increased cud chewing, salivation and thus N recycling to the rumen could account for the decrease in calculated N digestibility (Lapierre and Lobley, 2001; Table 2). Data obtained from the CPM-Dairy model suggested that BGS reduced microbial protein production in the rumen. Microbial protein production depends on amount of N and fermentable
carbohydrate supplied to the rumen (Leng and Nolan, 1984). A fibrous feedstuff such as BGS
has a low CP content as well as a low energy content, therefore BGS fermentation does not yield the same amount of microbial protein as a higher CP, higher energy feed such as alfalfa hay. Thus incorporation of BGS in the diet reduces the ability of microbes to synthesize microbial protein from the diet. A decrease in microbial protein production can result in an increase of ruminal bypass protein (Roseler et al., 1993). The CPM-Dairy model predicted a 10% increase in unavailable CP with the addition of BGS to the diet. Thus, the decrease in microbial production is indicative of a reduction in N digestibility by incorporating BGS into the diet.
Blood urea N was unaffected by inclusion of BGS, and although within the normal range of 8.0
to 22.4 mg/dL, values were high compared to target BUN values between 13 and 17 mg/dL for
cows producing 36 kg of milk per day (Lane and Campbell, 1966; Jonker, 1998). High levels of
BUN are indicative of inefficient N utilization by the cow, and can be caused by high levels of
dietary CP or inadequate amounts of readily digestible carbohydrate (Nousiainen et al., 2004).
Data obtained from the CPM-Dairy model suggest that the overall carbohydrate digestibility of
the BGS diet was lower and the amount of unavailable carbohydrate was higher than the controldiet . Kauffman and St-Pierre (2001) reported decreased efficiency of N utilization as dietary CP increased. The high BUN levels found in the current study are likely because both control and BGS diets were higher in CP (19.9 and 18.3%, respectively) than the recommended 16.5 to 17.5% of DM (NRC, 2001).
As dietary CP increases, BUN and MUN increase, hence BUN values were highly correlated
with MUN values. However, MUN was reduced in cows fed BGS though BUN was unaffected. Wang et al. (2007) reported MUN values of 9.8 mg/dL for cows fed diets containing 11.9% CP, and 19.1 mg/dL for cows fed 15.4% CP. Roseler et al. (1993) found that a decrease in dietary CP in the diet from 15.2 to 12.2% lowered the MUN levels to 5.6 mg/dL whereas an increase in CP to 17.6% increased MUN to 17.8 mg/dL. In the current study, a reduction in dietary CP by addition of BGS led to a reduction in MUN values. However fecal N excretion was not reduced. Urinary N excretion was not determined in this study. Yan et al. (2006)reported that lactating dairy cows consuming 486 g N/d and averaging 21.4 kg milk/d excreted 72.2% of N intake in the feces. However, Devant et al. (2000) reported dietary CP at 14 and 17%
of the diet DM had no effect on fecal N excretion in dairy heifers. Van Vuuren et al. (1993)reported increased fecal N values with increased levels of indigestible CP in the small intestine.
Fecal N was not affected by dietary treatment in the current study and supports the hypothesis
that urinary N excretion is more likely to reflect N intake than fecal N excretion. Fecal N is influenced by milk N secretion (Wilkerson et al., 1997). Wilkerson et al. (1997) reported a decrease in fecal N when milk yield increased, with secretion of N in the milk increasing as milk yield increased. Ideally, dietary CP levels are lower than the diets fed in the current study. BUN and MUN values were consistent with cows fed high CP diets, indicating that further measures to reduce dietary CP are needed.
Milk Yield and Composition
Previous studies have successfully incorporated low CP, high fiber feeds into lactating dairy cow
diets without affecting milk yield and DMI. Wu (2005) reported that milk yield was unaffected
in high producing dairy cows (97 DIM, 43 kg/d) when 10% soy hulls were substituted for 6% of
the alfalfa hay in the diet. Although soy hulls are a high fiber feed, their small particle size may result in fast ruminal passage and not reduce total DMI of cows. Wu et al. (2003) found that reducing dietary P (0.33 vs. 0.42% DM) and increasing the fiber portion of the diet (48% vs.
58% DM) did not affect DMI but lowered milk yield (34.0 vs. 36.5 kg/d). O’Rourke (2007)
reported that milk yield was unaffected by 10% inclusion of BGS in the diet in late lactation
cows. However, in the current study (114 DIM) average daily DMI was increased by 1.4 kg/d
and milk yield was reduced by 1.7 kg/d by 10% inclusion of BGS. The reduction in energy
content of the diet by addition of BGS caused cows to increase DMI to support milk production.
However, the increase in DMI was not sufficient to meet energy demands for lactation, and milk
yield was reduced. Although BGS-fed cows were not able to consume an adequate amount of
energy to support the same level of milk production as control-fed cows (P<0.05), serum NEFA levels were unaffected (Table 5). NEFA levels in cows in greater than 100 DIM are not sensitive to small dietary energy changes and, therefore, any dietary energy deficiency has to be fairly large for NEFA levels to increase (Martin and Sauvant, 2007). As BGS-fed cows did not utilize body fat stores, this finding indicates that incorporation of 10% BGS into the TMR did not result in a dramatic energy deficit and weight loss situation. Valk and Sebek (1999) investigated the effects of a low P diet (0.28% P) in lactating cows and found no effect on milk fat, protein and lactose, though milk yield was reduced. Likewise, Wu and Satter (2000) reported no effect on milk yield and milk composition in cows fed either 0.38 or 0.48% dietary P. In the current study, partial replacement of alfalfa hay with BGS did not affect concentration of milk components of fat, protein, lactose and somatic cell count. However solids-not-fat was reduced in BGS-fed cows. REFERENCES
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Educational & Outreach Activities
Huisman, Andrina Christine. 2009. The Effects of Reducing Dietary Phosphorus and Nitrogen by the Addition of Bluegrass Straw to the Rations of Early to Mid-Lactation Holstein Dairy Cows. M.S. Thesis, Washington State University, Pullman, WA.
Huisman, A.C., S. Cobb, R.L. Kincaid, J.J. Michal, and K.A. Johnson. 2009. The effects of reducing hdietary phosphorus by the addition of bluegrass straw to the rations of early to mid-lactation Holstein dairy cows. J. Anim. Sci. 87(E-Suppl.3):157.
Huisman, A.C., S.M. Cobb, J. Michal, and R.L. Kincaid. 2008. Effects of bluegrass straw on milk yield, intakes of crude protein and phosphorus, and income over feed costs in early to mid-lactation Holstein cows. Proc. 43rd Pacific Northwest Animal Nutrition Conference, pp.201, Tacoma, WA.
Inclusion of 10% BGS in the rations of early to mid-lactation dairy cows reduced the P and N content of the diet. However, because DMI increased in cows fed BGS, P intake was not affect although N intake was reduced. Sorting of the TMR by all cows contributed to intakes of P and N that were higher than expected. Although fecal P concentration was not affected, the %P in the diet was reduced by inclusion of BGS, giving producers an option for reducing P content of the ration. Feeding behavior and feed sorting were similar between treatment and control groups. Milk yield was reduced by inclusion of BGS but overall income over feed costs was unaffected. Reduced income from milk was compensated by the reduction in feed costs, indicating that finances are not impacted by inclusion of 10% BGS in the diet. Bluegrass straw reduced P intake and P excretion in diets of cows late lactation without affecting milk yield. The results of this study show that BGS is an acceptable feedstuffs that can be used to reduce N and P intakes of cows, particularly those in late lactation, and also can be used as a forage extender.
At the time of the trial, alfalfa cost $270/ton whereas bluegrass straw cost $85/ton. The reduction in feed cost from incorporation of bluegrass straw into the diet was $0.24/cow/day. Ath the time of the study, milk prices were $0.42/kg of milk. Yield of milk was reduced in the cows fed BGS and consequently income from milk was reduced as well. Although gross income was reduced, the overall income over feed costs was unaffected by the inclusion of bluegrass straw in rations of cows in early and mid-lactation.
Within the past 12 months there has been major changes in prices of forages, feed grains, milk and fuel. For example, alfalfa hay prices declined by nearly $100/ton and milk prices are significantly lower than their recent peak. Because the price difference between bluegrass straw and alfalfa hay has narrowed considerably, from nearly $200/ton to less than $100/ton currently, farmer intested has declined as well. However, nutritionists and farm nutrient management specialists continue to express interest in this and other strategies to reduce N and P excretion and subsequent soil accumulation on livestock farms.
Areas needing additional study
Ammonia emissions and P accumulation in soils remain important environmental challenges for concentrated animal feeding operations. Accordingly, there is urgent need for continued study into incorporating low N and P feedstuffs into production rations to reduce N and P intake and excretion by animals. Ideally, these feedstuffs will be local byproducts that are currently under-utilized and often burned to stockpiled until field disposal. With regard to bluegrass and other straws, suggested areas of future work include processing of straws by finer grinding or other methods to limit diet sorting by cows, and use of bluegrass and other straws in diets of dry beef and dairy cows.