PSX-8 Effects of synthetic eCG-like glycoprotein on follicular and luteal characteristics in primiparous beef cows with or without postpartum supplementation.

Abstract We evaluated the effects of a synthetic eCG-like glycoprotein on dominant follicle (DF) size and growth, ovulation rate (OR), corpus luteum (CL) size, and plasma progesterone concentrations in primiparous suckled Angus cows synchronized with a 5-d Co-Synch protocol, with or without postpartum protein supplementation. Thirty-two primiparous cows (BCS = 3.7 ± 0.2 [1-9 scale]; days postpartum = 20 ± 3.7) were randomly allocated to one of two dietary treatments for 82 days (from Day -47 to Day 35; Day 0 was the TAI day). The supplemented group (SUP) received ad libitum native grass hay (CP, 8.9 %; IVDMD, 52.4 %; ME, 1.7 Mcal/Kg) plus 2 kg of 28 % CP supplement per animal daily. The non-supplemented group (NSUP) received ad libitum native grass hay. On Day -8, all cows received a progesterone intravaginal device (1.0 g; IVD) and 100 μg GnRH. On Day -3, cows received 500 μg cloprostenol, IVDs were removed, and cows from each nutritional treatment were assigned randomly to eCG-like (400 IU eCG-like glycoprotein; Fixplan-R®, Syntex, Argentina) or Control group (no eCG-like). On Day -2, all cows received a second dose of 500 μg cloprostenol. On Day 0 (72 h post-IVD removal), cows received 100 μg GnRH and were inseminated. Cow BW on Days -47, -8, and 35 was analyzed using repeated measures in PROC MIXED, with day as the repeated effect. Dominant follicle size on Day -3 and 0, DF growth, CL size on Day 8, and progesterone concentrations on Day 8 were analyzed using PROC MIXED. Ovulation rate (evaluated on Day 8) was analyzed with PROC GLIMMIX using a binary distribution and logit link function. In all models, fixed effects included nutritional treatment (SUP vs. NSUP), hormonal treatment (eCG-like vs. Control), and their interaction, while pen was included as a random effect. There was an interaction between nutritional treatment and days (P = 0.01) on BW. On Day -47, BW was similar between nutritional treatments (331.4 and 329.8 ± 3.6 Kg for NSUP and SUP, respectively; P = 0.74). However, on Day 35, cows in the SUP group had greater BW than those in the NSUP group (316.1 and 329.4 ± 3.6 Kg for NSUP and SUP, respectively; P = 0.01). All cows were without a CL at the beginning of the ovulation synchronization protocol. Nutritional treatment did not affect (P > 0.1) follicular and luteal characteristics. Treatment with synthetic eCG-like glycoprotein increased (P ≤ 0.05) DF size on Day 0, DF growth rate, OR, CL size on Day 8, and progesterone concentrations on Day 8 (Table 1). These findings indicate that eCG-like glycoprotein improved follicular and luteal characteristics, regardless of nutritional treatment.