Effect of supplementation during the breeding season on a May-calving beef herd in the Nebraska Sandhills

Abstract

A 4-yr study at the Gudmundsen Sandhills Laboratory, Whitman, Nebraska, evaluated the effects of supplementation during the breeding season on May-calving heifers and primiparous cows. Beginning mid-July, and throughout a 45-d breeding season, heifers and primiparous cows grazed upland range and received either (1) no supplement (n = 128 heifers, 67 primiparous cows) or (2) 0.45 or 0.91 kg/animal per day for heifers and primiparous cows, respectively, of a 32% CP (DM) supplement (n = 129 heifers, 68 primiparous cows). Cows and heifers were synchronized using a single prostaglandin F_2α injection 5 d after bull placement (1:20 bull-to-cow ratio). Pregnancy was diagnosed via transrectal ultrasonography in mid-October or November for heifers and primiparous cows, respectively. Weaning occurred at pregnancy diagnosis. Body weight and BCS were taken at several time points throughout the year. Heifer BW and BCS following supplementation were unaffected by treatment (P ≥ 0.10). Primiparous cow BW and BCS were greater in supplemented cows at the time of pregnancy diagnosis (P < 0.01). Pregnancy rate was similar (P ≥ 0.41) between treatments for both age groups. Treatment did not affect calf BW at birth or dystocia rates for primiparous cows (P ≥ 0.17). Calf BW at weaning was greater (P < 0.01) for supplemented primiparous dams. Supplementation during the breeding season did not affect pregnancy rates in young beef females, despite BW and BCS changes in primiparous cows.