Abstract
The objectives were to evaluate the effects of recipient category, season and administration of a gonadorelin analogue at the time of fixed-time embryo transfer (FTET) on pregnancy per FTET at 30 and 60 days after oestrus and on pregnancy losses (PL). Recipients were randomly assigned to: treated group (n = 624), in which recipients received an intramuscular injection of 0.2 mg of gonadorelin (Fertagyl®) at FTET; or a control group (n = 687) that remained untreated. Recipients were previously treated with a synchronisation protocol based on progesterone and oestradiol. All embryos were produced in vitro. The data with binomial distribution were analysed by multivariate logistic regression, using the GLIMIX procedure of SAS. Higher P/FTET was observed at 30 days (45.8 vs. 40.0%; P = 0.03) and 60 days (43.0 vs. 37.0%; P = 0.01) in the treated group. There was a tendency toward reduced PL in the treated group (4.0 vs. 7.0%; P = 0.09). Dry cows (2.70%) and lactating cows (2.47%) had less PL (P = 0.001) compared with heifers (10.42%). In the spring/summer season the P/ FTET at 60 days was smaller (P =0.024). Greater PL tended to occur in the warmer season. Treatment with gonadorelin at the time of bovine ET increased the pregnancy per ET at days 30 and 60 and reduced PL. Additionally, dry and lactating recipient cows showed a lower PL rate compared to heifers. Furthermore, ET performed in the warmer seasons of the year resulted in a lower pregnancy rate at day 60 and greater PL.
Keywords:
reproductive efficiency; dairy cattle; reproduction