Effects of a low-protein, high-fiber supplement on performance, blood metabolites, and first-service AI conception rate in beef cows grazing lush pasture

Abstract Text: The objective of this study was to evaluate the effects of a dry, low-protein, high-fiber supplement on performance, blood metabolites, and first-service AI conception rates. Spring-calving, lactating Simmental and Simmental-Angus cows (n = 117) were stratified by breed and BW and allotted to 6 pastures. Pasture groups were randomly assigned to 1 of 2 treatments: control (CTRL, no supplement), and supplement (SUP, 1.8 kg supplement·cow^-1·d^-1). Supplement contained 45% ground corn cobs, 45% soybean hulls, and 10% dried molasses. Cows grazed tall fescue, orchard grass, red clover, and white clover mixed pasture for 70 d (April 28 to July 7, 2014). Clip samples were collected from new pastures as groups were rotated. Cows were bred via timed AI on d 10. Serum from d 0, 7, and 18 was pooled by pasture group within d and analyzed for NEFA, beta-hydroxybutyrate (BHBA), and blood urea nitrogen (BUN) concentrations. Conception rate was determined via palpation and ultrasound on d 45. Data were analyzed using the MIXED procedures in SAS (SAS Inst. Inc, Cary, NC) with repeated measures for CP, ADF, NDF, DM, NEFA, BHBA, and BUN. There were no treatment by time interactions (P ≥ 0.63), nor treatment effects (P ≥ 0.07) for pasture composition. Over time, CP decreased (P < 0.01); however, ADF (P < 0.01) and NDF (P < 0.01) increased. Over time, DM did not differ (P = 0.20). Treatment did not affect final BCS (P = 0.97) and BW (P = 0.77). There was no difference (P = 0.83) in percentage of cows cycling prior to estrus synchronization between treatments (CTRL, 68%; SUP, 69%). There were no treatment by time interactions (P ≥ 0.45) for NEFA or BUN. Treatment did not affect (P = 0.80) serum NEFA concentrations. Serum concentration of BUN tended (P = 0.09) to be greater in CTRL cows compared to cows fed SUP. There was a treatment by time interaction (P =0.02) for BHBA. On d 10, serum concentrations of BHBA were greater (P < 0.01) for cows fed SUP compared to CTRL cows; however, on d 18, there were no differences (P  = 0.66) between treatments. There was no difference (P = 0.64) in conception rate between treatments (CTRL, 38.5%; SUP, 51.7%). In conclusion, a low-protein, high-fiber supplement did not affect BW and BCS, or significantly improve first-service AI conception in cows grazing lush pasture in early spring. 

Keywords:

beef cow, reproduction, supplementation