108 Pregnancy rates to embryo transfer in lactating Bos indicus × Bos taurus dairy cows synchronized with a new gonadotropin-releasing-hormone based protocol with lengthened proestrus

This experiment evaluated recipients utilisation rate and pregnancy outcomes to embryo transfer (P/ET) in lactating Bos indicus × Bos taurus cows (Gyr × Jersey) synchronized with an oestradiol-based protocol or with a new GnRH-based protocol with a lengthened proestrus (named “Web-Synch”). Lactating cows (n = 1456) with 55.0 ± 12.0 days in milk, a corpus luteum (CL) or at least one follicle >8 mm in diameter (determined by ultrasonography), a body condition score between 2.5 and 4 (1–5 scale) and managed in a confinement system, were randomly allocated into one of two treatment groups. On Day 0, cows in the J-Synch group (n = 711) received 2 mg of oestradiol benzoate (EB, Calier) and an intravaginal device containing 1.2 g of progesterone (P4, Pluselar, Calier). On Day 6, P4 devices were removed, and all cows received 150 µg D (+) cloprostenol (PGF, Veteglan, Calier), 400 IU of equine chorionic gonadotropin (eCG; Vetegon, Calier). Cows in the Web-Synch group (n = 675) were treated with prostaglandin F_2α (PGF) and P4 device on Day −5, 10 µg of buserelin (GnRH, Pluserelina, Calier) on Day 0 and P4 device removal, PGF and eCG on Day 6. All cows were observed for signs oestrus, which was based on tail-paint removal (>50%), by 72 h after P4 device removal. In those detected in oestrus their ovaries were examined by ultrasonography (Mindray M6 Vet) on Day 16 and those with a CL >16 mm in diameter received a grade 1 in vitro-produced blastocysts by nonsurgical transfer. Recipients without their tail-paint removed were not transferred. Pregnancy was determined by ultrasonography 30 and 90 days after embryo transfer. Data were analysed using the GLM mixed procedure for binary data with a logit link (InfoStat, 2022) and results are presented in Table 1. Although the utilisation rate did not differ among groups, the Web-Synch protocol resulted in greater P/ET that the J-Synch protocol.