Effects of an eCG-like glycoprotein treatment and nutritional status on reproductive performance in suckled beef cows subjected to a progesterone-based 7-d Co-Synch protocol

Abstract

The objective of the present study was to evaluate the effects of a synthetic eCG-like glycoprotein treatment, body condition score changes, and postpartum nutritional supplementation on follicular and luteal characteristics and pregnancy rates in suckled beef cows synchronized with a 7-d Co-Synch protocol. In Experiment I, 1218 suckled cows received a progesterone intravaginal device (1.0 g; IVD) and 100 μg GnRH on Day 10. On Day 3, IVDs were removed, and cows received 0.5 mg sodium cloprostenol and were randomly assigned to receive either 400 IU eCG-like glycoprotein (eCG-like; n = 602) or no eCG-like glycoprotein (Control; n = 616). On Day 0, 100 μg GnRH was given concurrently with TAI. Body condition score (BCS) was recorded on Day 10 and 35, and its change was calculated. Corpus luteum (CL) presence was evaluated on Day 10, and pregnancy (P/TAI) on Day 35. In cows without CL, eCG-like increased estrus expression rate (EER; 58.2 vs. 45.3 %; P = 0.01). In cows that lost BCS, eCG-like increased P/TAI (47.2 vs. 32.1 %; P = 0.01). In Experiment II, 72 cows, 21 d postpartum, were assigned to supplemented (SUP; 4 kg of corn daily) or non-supplemented (NSUP) diets for 80 days. Cows were subjected to the same synchronization protocol and eCG-like glycoprotein treatment described in Exp. I. Nutritional SUP increased (P ≤ 0.05) body weight and BCS. Dominant follicle (DF) growth tended to be greater in eCG-like group than Control (1.2 vs. 0.7 ± 0.3 mm/d; P = 0.08), while the SUP group exhibited greater ovulation rate and CL area compared with NSUP (P ≤ 0.03). The eCG-like treatment increased EER in cows without CL and P/TAI in those losing BCS. Although eCG-like tended to improve DF growth, no interaction was observed between nutritional and eCG-like treatment on follicular and luteal characteristics.