Effects of Prepartum Whole Fuzzy Cottonseed or Whole Raw Soybean Supplementation on Response to Timed Artificial Insemination by Suckled Mature Beef Cows Following Ovulation Synchronization1

Cows (n = 188; average initial BW = 579±54 kg) were stratified by BCS and BW and assigned to 3 supplementation treatments: whole raw soybeans (21.6% fat), whole fuzzy cottonseed (21.7% fat), or a 50:50 mixture of ground corn and soybean meal (2.6% fat; i.e., the control supplement). Supplements were fed daily at 1.8 kg/cow for 45 d before the first projected calving date. Supplementation was continued until calving. Ovulation was synchronized using the Cosynch + controlled internal drug release (CIDR) protocol (injection of GnRH 7 d before and 64 h after a 7-d intravaginal CIDR insert containing 1.38 g of progesterone) and a 25-mg injection of PGF2α. Cows were inseminated artificially at 60 to 64 h after CIDR removal. Eleven days after AI, cows were exposed to fertile bulls for natural-service breeding for 50 d. Conception to AI was assessed 33 d after AI; overall pregnancy rate was assessed 126 d after AI. Body weight of cows fed control or oilseed supplements was similar (P > 0.3) at calving, at initiation of ovulation synchronization, and at the end of the breeding season. Cottonseed-supplemented cows lost more BW and more BCS (P < 0.03) from the onset of supplementation until calving than those fed soybeans. Proportion of cows with estrus cycles was similar (P = 0.57) among treatments. Pregnancies per fixed-time AI and final pregnancy rate were similar (P ≥0.75) between control and oilseed-supplemented cows. Conversely, supplementation with cottonseed tended (P = 0.08) to increase pregnancies per timed AI (54 and 39% for cottonseed and soybeans, respectively) and increased (P = 0.03) final pregnancy rate compared with soybean-fed cows (100 and 93% for cottonseed and soybeans, respectively). In conclusion, cows supplemented with whole, fuzzy cottonseed tended to have a greater timed AI pregnancy rate and had a greater final pregnancy rate than cows supplemented with whole, raw soybeans. Effects of cottonseed and soybean supplementation on response to ovulation synchronization and fixed-time AI by beef cows warrant further study.