Effect of supplementation on performance and reproduction of lactating beef cows grazing lush spring pasture

The Professional Animal Scientist 32 (2016):798–804; http://dx.doi.org/10.15232/pas.2016-01506 ©2016 American Registry of Professional Animal Scientists. All rights reserved.

E fperformance fect of supplementation on and reproduction of lactating beef cows grazing lush spring pasture

K. Doungkamchan,* M. S. Jarboe,* L. M. Shoup,* W. T. Meteer,† PAS, W. P. Chapple,* and D. W. Shike*1 *Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana 61801; and †University of Illinois Extension, Orr Research and Demonstration Center, Baylis 62314

ABSTRACT Our objectives were to use 230 Angus × Simmental beef cows in a 2-yr experiment to determine the effects of supplementation on cow BW and BCS, firstservice AI conception rate, and blood metabolites (nonesterified fatty acids, BHBA, and BUN). Cows (110 in yr 1 and 120 in yr 2) were randomly assigned to 1 of 2 treatments: control or supplement (SUPP). There were 3 replicates per treatment each year, and both treatments grazed clover–tall fescue pasture in early spring. The supplement contained 45% ground corncobs, 45% soybean hulls, and 10% dry molasses (DM basis), and 1.81 kg/cow per d was offered to cows fed SUPP starting 10 d before breeding. Forage samples were collected as groups were rotated to new pastures. Throughout the grazing season, forage CP decreased (P < 0.01), whereas ADF and NDF increased (P < 0.01). Day-18 BUN concentration in yr 2 tended to be decreased (P = 0.10) in cows fed SUPP compared with control cows. Concentration of BHBA for cows fed SUPP tended to be greater (P = 0.07) compared with

Corresponding author: [email protected]

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control cows; however, nonesterified fatty acids did not differ (P = 0.80). There was no difference (P ≥ 0.44) in final BW and BCS nor was there any difference (P ≥ 0.35) in AI conception and overall pregnancy rate. In conclusion, a high-fiber, low-protein supplement did not affect BW or BCS or significantly improve first-service AI conception rate and overall pregnancy rate in cows grazing lush, early-spring pasture. Key words: beef cow, cool-season pasture, excess protein, supplementation, reproduction

INTRODUCTION The majority of beef producers have spring-calving herds so as to take advantage of spring pasture growth when nutrient demands of the dam are at their peak. Because nutrition and reproduction are closely tied together (Hess et al., 2005), it is important to consider the nutritional status of cows as rebreeding approaches. For spring-calving cows, breeding often coincides with lush, highly palatable, immature pasture. These immature forages usually contain a high N content and fewer carbohydrates. Due to

the imbalance of N and carbohydrate and the high moisture contents of the forage, cows often enter a negative energy balance (Arelovich et al., 2003). In lactating dairy cows, high dietary CP has also been shown to reduce fertility and the viability of embryos due to the interaction between negative energy balance and excess protein (Butler, 2005). Previous research has indicated that a BUN concentration of more than 20 mg/dL (Hammon et al., 2005) alters the uterine environment, decreases the survival of spermatozoa (Westwood et al., 1998), and decrease ability of oocytes to develop to blastocysts (Santos et al., 2009). Several supplementation strategies have been considered to alleviate the effects of the reduced energy balance due to grazing lush pasture. In the southeast United States, supplementation of cottonseed meal improved ADG of steers grazing during a 39-d period from December through January (Worrell et al., 1990) and improve N utilization of microbes in a continuous culture system (Bach et al., 1999). Little work has been done to evaluate the effect of feeding a supplement during early lactation on AI conception of beef cows grazing lush pasture.

Effects of supplementing beef cows grazing spring pasture

Therefore, the objectives of this experiment were to evaluate the effects of supplementation on cow BW and BCS, first-service AI conception rate, and blood metabolites [nonesterified fatty acids (NEFA), BHBA, and BUN]. We hypothesized that a dry, low-protein energy supplement would improve first-service AI conception rate and overall production performance of beef cows by serving as a dilutor of the high-N pasture forage and reducing the negative effects of an imbalanced protein-to-energy ratio.

MATERIALS AND METHODS Animals in this trial were cared for in accordance with guidelines in the Guide for the Care and Use of Agricultural Animals in Agriculture Research and Teaching (FASS, 1988). Experimental procedures followed those approved by the University of Illinois Laboratory Animal Care Advisory Committee, protocol 15008. The experiment was conducted from April 29, 2013, through July 1, 2013, and April 28, 2014, through July 7, 2014, at the University of Illinois Orr Beef Research Center, Baylis, Illinois.

Animals, Experimental Design, and Treatments A total of 230 Angus × Simmental lactating beef cows (initial BW = 662 ± 78 kg; initial BCS = 5.8 ± 1.5; average initial age = 6.03 yr within 3–13 yr range) were used in a 2-yr experiment. Cows (110 in yr 1 and 120 in yr 2) were stratified by initial BW and age and allocated into 6 pasture groups (20 cows per group) each year. Each pasture group was randomly allotted to 1 of 2 treatments: control or supplement (SUPP). Each SUPP group received 1.81 kg/cow per d of a supplement for a total of 67 ± 5 d, which began 10 d before breeding. The supplement contained 45% ground corncobs, 45% soybean hulls, and 10% dry molasses (DM basis). Supplementation began 56 ± 12 d and 60 ± 14 d postpartum for cows in yr 1 and yr 2, respectively (average

calving date was February 21, 2013, and February 25, 2014). Supplementation began at the end of April when cows were turned out to pastures. As typical in a springcalving herd, breeding often coincides with turnout to spring pastures. Cows were turned out to pastures 10 d before breeding when forage was at a lush, vegetative stage of maturity. Cows grazed pastures with an average coverage area of 30% red clover (Trifolium pratense) and white clover (Trifolium repens), and 70% endophyte-infected fescue (Festuca arundinacea) in each pasture. Total endophyte percentage of the fescue was 64%, as determined by a commercial laboratory (Agrinostics Limited Co., Watkinsville, GA). Each group was rotated between 3 pastures every 10 to 17 d, and all groups were moved the same day. All groups were moved 5 times throughout the supplementation period. Average pasture size was 4.2 ± 0.9 ha for control groups and 4.3 ± 1.1 ha for SUPP groups. Average stocking rate was 5.0 ± 1.28 and 5.1 ± 1.58 cow-calf pairs/ha for control and SUPP groups, respectively. A calibrated (Tracy and Faulkner, 2006) electronic plate meter (Jenquip, Fielding, New Zealand) measurement was collected daily throughout the supplementation period in both yr 1 and 2 of the experiment. A total of 20 measurements were taken every 6.1 to 12.2 m in a zigzag pattern across the pasture. The pattern was designed to cover the entire pasture uniformly regardless of area distribution within the pasture. An average of 20 readings were recorded, and an estimate of forage coverage was obtained. Groups were moved when approximately 25% of the available forage had been consumed. Average pregraze forage coverage was 4,335 ± 1,362 kg of DM/ha for control groups and 4,356 ± 1,183 kg of DM/ha for SUPP groups. Average postgraze forage coverage was 3,124 ± 683 kg of DM/ha for control groups and 3,253 ± 855 kg of DM/ha for SUPP groups. A commercial mineral (#CP63, Pike Feeds, Pittsfield, IL; 12 to 14% Ca,

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8% K, 18 to 20% NaCl, 11% Mg, 90 mg/kg of I, 528,000 IU/kg of vitamin A, 88,000 IU/kg of vitamin D3, and 2,200 IU/kg of vitamin E) and water were also offered for ad libitum consumption throughout the experiment. Cows were commingled after the end of the supplementation period and grazed common pasture (red clover, white clover, and endophyte-infected fescue). Cows were weighed on 2 consecutive days at the beginning (d 0 and 1 of supplementation) and end of the experiment (d 66 and 67 of supplementation). Body condition score was also determined at d 0 and d 67 ± 5 of supplementation.

Estrus Synchronization and AI Cows were synchronized using 7-d CO-Synch + controlled internal drugrelease (CIDR; Zoetis Services LLC, Parsippany, NJ) procedure (Johnson and Dahlke, 2016) method. At d 0 of supplementation (10 d before breeding), CIDR implants and Cystorelin (Merial Limited, Duluth, GA; gonadotropin-releasing hormone) injections were applied to all cows. After turning cows back to pastures, at d 7 of supplementation, CIDR were removed and Lutalyse (Zoetis Services LLC; prostaglandin) was injected into all cows. At d 10 of supplementation, all cows were artificially inseminated and turned back to pastures. In yr 1, one bull was added to each pasture group 14 d after AI and remained there for 35 d. In yr 2, one bull was added to each pasture group 11 d after AI and remained there for 61 d. Pregnancy verification to AI was performed 34 d after AI in yr 1 and 35 d after AI in yr 2. Overall pregnancy check was performed 32 d after bull removal in yr 1 and 34 d after bull removal in yr 2. Pregnancy was confirmed by a trained technician via ultrasonography (Aloka 500 instrument, Wallingford, CT; 7.5-MHz general purpose transducer array).

Blood Sampling and Analysis In yr 1, serum samples collected on d 0 and 7 of supplementation were

800 pooled by pasture group and analyzed for BUN. In yr 2, serum samples collected on d 0, 7, and 18 of supplementation were pooled by pasture group and analyzed for BUN, NEFA, and BHBA concentrations to indicate excess protein intake and reduced energy status. In both years, blood was collected using a 38-mm needle into a 10-mL Vacutainer (Becton, Dickinson and Co., Franklin Lakes, NJ) and stored on ice immediately. The blood samples were then centrifuged (Model HN-S, International Equipment Company, Needham Heights, MA) at 1,300 × g for 40 min at 20°C for serum collection. Serum was immediately frozen at −20°C until analysis. In yr 2, individual serum samples from d −10 and 0 of supplementation were analyzed for progesterone concentration to determine cyclicity. Serum progesterone concentration was analyzed by RIA using a CoatA-Count kit (Siemens Healthcare Diagnostics Inc., Los Angeles, CA). Validation and methods used are described further by Shoup et al. (2015). Estrous cyclicity was verified when serum progesterone concentration met or exceeded 1 ng/mL in at least 1 of the 2 samples. Serum samples from d 0 and 7 of supplementation in yr 1 were kept frozen before analysis for BUN concentration. Analysis of BUN was determined via a QuantiChrom Urea Assay Kit (DIUR-500; BioAssay Systems, Hayward, CA). Intra- and interassay CV was 7.2 and 10.3% for 3 assays, respectively, for BUN analysis. Serum samples from d 0, 7, and 18 of supplementation in yr 2 were kept frozen before analysis for BUN, NEFA, and BHBA concentration. Composited serum samples were delivered to the University of Illinois, College of Veterinary Medicine Diagnostic Laboratory. Serum BHBA, NEFA, and BUN concentrations were analyzed using an Olympus AU680 Chemistry-Immuno Analyzer (Olympus Corporation, Center Valley, PA). Analysis of NEFA was conducted via a colorimetric assay [HR Series NEFA-HR (2); Wako Chemicals, Richmond, VA]. Colorimetric analyses

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were also used for BUN (OSR6134; Beckman Coulter, Indianapolis, IN) and BHBA concentration determination (Ranbut; Randox, Crumlin, UK).

Forage and Feed Sampling and Analysis Forage samples were collected each time cows were moved into pastures. A total of 4 samples per pasture were collected at random by tossing a 0.61-m-diameter wire loop. Forage height within the wire loop was measured using a yardstick and was clipped 7.6 cm above the ground to imitate grazing cows. Supplement samples were collected weekly and composited for analysis. The forage and supplement samples were dried in a 55°C oven for 3 d. The dry samples were ground using a Wiley Mill (Arthur H. Thomas, Philadelphia, PA) through a 1-mm screen. The supplement was composited across the supplementation period. The 4 forage samples from each pasture were composited. All composited samples were analyzed for CP (Leco TruMac, LECO Corporation, St. Joseph, MI), ADF and NDF (method 5 and 6, respectively; Ankom200 Fiber Analyzer, Ankom Technology, Macedon, NY), and ash (600°C for 2 h, Thermolyne muffle oven model: F30420C, Thermo Scientific, Waltham, MA). Total digestible nutrients was back-calculated from ADF using TDN = 93.59 − (ADF × 0.936) as suggested at http://www. clemson.edu/agsrvlb/Feed%20formulas.txt.

Statistical Analysis Pasture group was the experimental unit in all statistical analyses. Pasture data were analyzed using the MIXED procedure of SAS (SAS Institute Inc., Cary, NC) to evaluate differences in DM, CP, ADF, and NDF between forages in control and SUPP pastures. Year was included as a random effect, and time point and treatment were included as fixed effects. The REPEATED statement was used to model the repeated measurements within pasture

group, and the compound symmetry covariance structure was selected after considering the Akaike and Bayesian information criteria. Body weight, BCS, and blood metabolite data were also analyzed using the MIXED procedure. Year was included as a random effect and treatment as a fixed effect in the model for the performance data. Analysis of NEFA and BHBA included only time and treatment as fixed effects in the model because these data were only collected in yr 2. For BUN, year was included as a random effect. The REPEATED statement was used to model the repeated measures within pasture group, and the appropriate covariance structure was selected (simple for NEFA, heterogeneous compound symmetry for BHBA and BUN) after considering the Akaike and Bayesian information criteria. The concentration of NEFA at d 0 differed by treatment; therefore, d 0 was included in the model as a covariate for NEFA analysis. For BUN, only d-0 and d-7 data were analyzed using the REPEATED statement, and year was included as a random effect. The d-18 BUN data from yr 2 were analyzed separately in the MIXED procedure of SAS so as to avoid confounding d-18 and year effects. Binomial data for cyclicity, AI conception, and overall pregnancy data were analyzed using the GLIMMIX procedure of SAS. Treatment was included as a fixed effects. For AI conception and overall pregnancy rate, random effects were year and pasture group. The PDIFF statement was used to separate least squares means at significance of P ≤ 0.05 and trends at P > 0.05 to ≤0.10.

RESULTS AND DISCUSSION Forage Nutritional Profile Nutrient composition of pasture forage and supplement are displayed in Figure 1 and Table 1, respectively. Percentage of forage 100°C DM, NDF, and ADF all changed over time (P < 0.01) but did not differ between treatments (P ≥ 0.33). Average NDF and

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Table 1. Cow supplement Item Ingredient, %   Ground corncobs   Soybean hulls   Dry molasses Nutrient content, %  DM  CP  NDF  ADF Calculated energy content  TDN1

Inclusion, % DM   45 45 10   87.9 8.1 66.7 43.0   53.3

Total digestible nutrients was backcalculated from ADF using TDN = 93.59 − (ADF × 0.936).

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ADF of the pastures at d 0 were approximately 43 and 25%, respectively. These results are comparable to Steen et al. (1979), who maintained tall fescue pastures in a vegetative state and found average NDF and ADF to be approximately 50 and 30%, respectively, in late April in Kentucky. Percentage of CP declined over time (P < 0.01) and also tended (P = 0.06) to be greater for control cows. Forage CP was greater than 12% throughout the entire supplementation phase and was at or greater than 20% during the first 10 d of supplementation (10 d before AI). This is comparable to the very early vegetative levels of CP found in late-March fescue sampled in Kentucky, which averaged approximately 22% CP (Steen et al., 1979) or 24% (Beck et al., 2008). By 24 d of supplementation, CP had declined to approximately 17%, which is similar to CP content of fescue sampled in other studies (Steen et al., 1979; Beck et al., 2008) when sampled later in the spring. These NDF, ADF, and CP results indicate that the pastures used in this experiment were vegetative when supplementation began in late April. As the spring commenced, NDF and ADF increased and CP decreased, which is indicative of forage maturity. However, the most critical time period of challenging the cows with lush pas-

Figure 1. Crude protein, DM, NDF, and ADF of pasture forage sampled over 70 d fed to cows receiving either no supplement (control) or 1.81 kg/cow per d of supplement (SUPP) in a 2-yr experiment. Forage was sampled from the end of April through early July in 2013 and 2014. Time was significant for all variables (P < 0.01). There was no (P ≥ 0.16) treatment and treatment × time point interaction for any variable, with the exception of CP, which tended (P = 0.06) to be greater in control pastures compared with SUPP pastures. Error bars = SEM.

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ture at the time of AI was achieved. The CP content for the first 10 d of supplementation would have exceeded the threshold of a diet high in CP as defined by Butler (2005; 17–19%), which has been associated with decreased reproductive performance (Butler, 2005).

Metabolite Concentrations in Blood Serum Blood metabolite results are shown in Figure 2. For d-0 and d-7 data, there was no (P = 0.52) treatment × time point interaction for BUN nor was there a difference (P = 0.20) in BUN over time. Concentrations of BUN were not different (P = 0.20) in cows fed SUPP compared with control cows on d 0 or 7. At d 18, there was a tendency (P = 0.10) for control cows to have an increased BUN compared with cows fed SUPP in yr 2. The difference in BUN concentration between the control cows and cows fed SUPP may be due to the diluting effect of the low-protein supplement provided to the cows fed SUPP. A similar diluting effect has been observed in other studies with steers grazing subirrigated pasture that were provided an energy supplement (Lake, 1974). However, BUN concentration at all time points failed to meet or exceed 20 mg/dL, the threshold classified by Hammon et al. (2005) as resulting in decreased reproductive performance. This was not anticipated because the CP content of the forage was classified as high and suitable for a dietary protein challenge, as mentioned by Butler (2005). There was no (P = 0.95) treatment × time point interaction for NEFA concentration. At both d 7 and 18, control cows and cows fed SUPP had similar (P = 0.80) NEFA concentration of approximately 0.30 mmol/L. There was no (P = 0.30) treatment × time point interaction nor (P = 0.26) effect of time for BHBA. There was a tendency (P = 0.07) for control cows to have reduced BHBA compared with cows fed SUPP. Negative energy status can be indicated by increased concentrations of

Figure 2. Serum concentration of nonesterified fatty acids (NEFA), BHBA, and BUN of cows receiving either no supplement (control) or 1.81 kg/cow per d of supplement (SUPP) in a 2-yr experiment. No (P ≥ 0.20) treatment × time point interaction existed for any of the 3 variables. *There was a tendency (P = 0.07) for treatments to differ for BHBA concentration. †Concentration differed at d 0 so included as a covariate. ‡Data from yr 2 only. #Tendency (P = 0.10) for treatments to differ at d 18 (BUN measured on d 18 in yr 2 only). Error bars = SEM.

Effects of supplementing beef cows grazing spring pasture

Table 2. Effect of supplementation on cow performance and AI conception Treatment1 Item BW, kg  Initial2  Final3 BCS  Initial2  Final3 Cycling,4 % AI conception rate,5 % Overall pregnancy rate,6 %

Control  

661 654   5.8 5.8 67.8 45.8 91.5

SUPP  

662 659   5.8 5.9 69.5 57.8 93.1

P-value, Treatment

SEM  

3 11   0.6 0.6 — — —

 

0.69 0.44   0.49 0.60 0.88 0.35 0.69

Control = no supplementation; SUPP = 1.81 kg/cow per d. Collected at d 0 of supplementation; 56 ± 12 d and 60 ± 14 d postpartum for yr 1 and 2, respectively. 3 Collected at d 71 of supplementation; 127 ± 12 d and 131 ± 14 d postpartum for yr 1 and 2, respectively. 4 Progesterone analyzed in yr 2 only. 5 34 ± 0.7 d after AI. 6 33 ± 1.4 d after bull removal. 1 2

NEFA (Richards et al., 1989), which reflect the magnitude of mobilization of fat from storage (LeBlanc et al., 2010). According to Garverick et al. (2013), dairy cows with a NEFA concentration greater than 0.20 mmol/L will use more adipose tissue to meet their energy requirement and are more likely to experience BCS loss. The average NEFA concentration of the cows in this experiment, approximately 0.25 to 0.30 mmol/L, also aligns with other work with beef cows experiencing an energy deficit. Grimard et al. (1995) fed beef cows a control energy (100% energy and protein requirement) and low energy (75% energy and protein requirement) diet after parturition until 70 d postpartum. Concentration of NEFA in the control cows was approximately 0.168 and 0.309 mmol/L in the cows fed low energy. The NEFA concentrations of the cows in this experiment are more similar to the concentrations of the cows fed low energy (Grimard et al., 1995), which indicates that these cows were in an energy deficit. β-Hydroxybutyrate is a ketone body used to reflect the completeness of fat oxidation in the liver (LeBlanc et

al., 2010). A high NEFA concentration (>0.4 mmol/L) is associated with an increased BHBA concentration because the liver is unable to oxidize the fatty acids at a fast enough rate (LeBlanc et al., 2010). A healthy cow should have a BHBA concentration of less than 1,200 μmol/L (or 1.20 mmol/L; LeBlanc et al., 2010). Greater concentrations of BHBA have been associated with poorer milk production and reduced reproduction performance (LeBlanc et al., 2010). The BHBA concentration of the cows on this experiment (0.2–0.3 mmol/L) indicate that the cows were not ketotic. Overall, it appears that, due to the increased NEFA concentration, the cows were in a negative energy balance. But, their BHBA levels were normal, so their livers were able to accommodate the increased fatty acid oxidation.

Performance and Conception Rate Cow performance is shown in Table 2. Initial BW, initial BCS, final BW, and final BCS did not differ (P ≥ 0.44) between control cows and cows

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fed SUPP. Few studies have been conducted evaluating supplementation to beef cows grazing lush spring pasture. This is likely because supplementation is most often a strategy used when standing range or pasture forages do not adequately meet the requirements of the cow (Adams et al., 1996). Highquality forage in late spring is typically of such adequate CP that it is sufficient to meet their needs (Adams et al., 1996). Some studies have evaluated growth performance of growing cattle grazing lush, cool-season pasture. Worrell et al. (1990) reported that steers supplemented 0.45 kg/d cottonseed meal did not differ in ADG from nonsupplemented steers later in the spring period. However, other studies provided a corn supplement (Lake, 1974) or barley supplement (Anderson and Dunn, 1982) to steers grazing pasture and found a significant improvement in ADG. But, differences in performance would be expected because both amount (>2.0 kg/d) and type of supplement (corn or barley) differed from the supplement used in this experiment. Percentage of cows cycling before breeding, AI first-service conception rate, and overall pregnancy rate did not differ (P ≥ 0.35) between control cows and cows offered SUPP. These findings contradicted our hypothesis that, based on the high N content of the forage and increased BUN of the control cows, AI conception rate would be decreased compared with the cows offered SUPP. There was a 12% numerical difference in AI conception rate, but this was not statistically different. These findings may be partially explained by the declining CP content in the forage over time as well as the fact that BUN concentrations were below the threshold of 20.0 mg/dL (Hammon et al., 2005). Gunn et al. (2014) fed diets differing in protein and found differences in BUN, but these differences did not carry through to significant differences in pregnancy rate. However, as in our experiment, BUN concentration at time of AI was below the threshold associated with decreased fertility (20

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mg/dL; Gunn et al., 2014). However, a BUN beyond the threshold does not always result in significant reproductive performance differences as Moriel et al. (2012) found. Dry-lot cows fed poor or medium quality hay had BUN concentrations of 17.2 and 22.8 mg/ dL, respectively, but had only an 8% numerical difference in pregnancy rate (Moriel et al., 2012).

dx.doi.org/10.3168/jds.S0022-0302(99)752197.

IMPLICATIONS

FASS. 1988. Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching. FASS, Champaign, IL.

Supplementation of a dry, lowprotein feedstuff to cows grazing lush spring pasture tended to reduce BUN at d 18 but did not significantly improve performance or reproductive measures. It is possible that if peak forage CP would have more closely aligned with breeding and implantation and if there were greater replication of cow groups, the results would have been statistically different. Further research is warranted to explore this topic further.

ACKNOWLEDGMENTS There was no external funding for this research.

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