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.