Reproductive Performance of Beef Cows Fed Whole Soybeans Before the Breeding Interval

Effects of feeding soybeans before breeding were determined using primiparous (PC) and multiparous (MC) Angus (PC = 17; MC = 36) and Polled Hereford (PC = 12, MC = 11) cows randomly assigned to control (no supplementation) or cracked whole soybean (2.12 kg DM/cow daily) treatments from February 11 to April 11. The breeding interval began April 14, using AI (d 1 to 44) and natural service (d 45 to 71). Calf ADG during the prebreeding period and during the interval from d 1 to weaning at d 210 was unaffected by treatment (P > 0.10). Calf breed affected (P < 0.01) calf prebreeding ADG, 210-d ADG, and 205-d weaning BW, which, respectively, were 1.18, 0.92, and 230.6 kg for Angus, and 1.01, 0.83, and 211.8 kg for Polled Hereford. Pregnancy rates were unaffected (P > 0.10) by treatment, cow breed, or parity. On d 60, serum triglyceride was greater for cows fed soybeans than for control cows (P < 0.01; 31.2 vs. 27.0 mg/dL), and serum cholesterol was affected by a treatment × parity interaction (P < 0.05), with respective values for control PC and MC and soybean treatment PC and MC of 134.6, 176.2, 195.8, and 201.5 mg/dL. Serum leptin levels on d 60 for these respective treatments were 5.4, 9.0, 8.4, and 8.6 ng/mL, with the lowest (P < 0.05) concentration in control PC cows. Feeding soybeans to PC cows resulted in increased serum leptin (P < 0.05), and PC cows fed soybeans had similar serum triglyceride, cholesterol, and leptin levels compared with MC for these variables.