391 EFFECTS OF SEASON AND LACTATION STATUS ON EMBRYO PRODUCTION IN HOLSTEIN COWS

Abstract

The aim of this study was to evaluate effects of season and lactation status on embryo production in Holstein donors (n = 51). Data from 195 embryo collections (94 from lactating cows and 101 from non-lactating cows), at a dairy farm located in Descalvado, Sao Paulo, Brazil, in 2005, were analyzed. The superstimulation protocol included two 3-mg norgestomet ear implants (Crestar^®; Intervet, Sao Paulo, Brazil) and an injection of 3 mg of estradiol benzoate IM (EB) on random days of the estrous cycle. Four days later, 500 IU FSH IM (Pluset^®; Calier, Buenos Aires, Argentina) were divided into 8 decreasing doses given 12 h apart. With the seventh FSH injection, 0.530 mg IM of sodium cloprostenol (PGF_α Ciosin^®; Coopers-Brazil, Sao Paulo, Brazil) was given, and implants were removed with the eighth FSH injection. Twelve hours later, 250 µg IM of gonadorelin (Fertagyl^®; Intervet) was given, followed by two AI 12 and 24 h later. Ova/embryos were recovered 6.5 days after the first insemination. The total number of ova/embryos, IETS grades 1, 2, and 3 (viable) and grade 4 plus unfertilized (non-viable), were analyzed by General Linear Model (GLM). Effects of donor, lactation status (lactating or non-lactating), sire, season (1: January through March, n = 56; 2: April through June, n = 37; 3: July through September, n = 50; 4: October through December, n = 52), and their interactions were included in the model. There was an effect of donor on all outcome variables (P < 0.01). There was an effect of season on the total number of ova/embryos (1: 10.2 ± 1.2; 2: 6.6 ± 1.0; 3: 10.0 ± 1.1; 4: 11.2 ± 1.2; P < 0.02) and of viable embryos (1: 3.7 ± 0.5; 2: 2.4 ± 0.5; 3: 5.9 ± 0.9; 4: 4.4 ± 0.7; P < 0.001). Lactation status influenced the total number of ova/embryos (lactating: 10.9 ± 0.9 vs. non-lactating: 8.7 ± 0.7; P < 0.001) and the number of non-viable embryos (lactating: 6.7 ± 0.8 vs. non-lactating: 4.4 ± 0.5; P < 0.01). However, there was no effect of lactation status on the number of viable embryos (lactating: 4.14 ± 0.5 vs. non-lactating: 4.29 ± 0.5; P > 0.10). In summary, the number of viable embryos in Holstein cows was influenced by season and donor, but not by lactation status.