Aplicação de agonistas de GnRH no momento da transferência de embriões produzidos in vitro em vacas holandesas

Abstract

High milk production may impair reproduction efficiency in Holstein cows by lowering circulating progesterone. The transfer of in vitro derived embryos in addition to GnRH agonist treatment may improve pregnancy rates in lactating Holstein cows. It was hypothesized that the intramuscular (i.m.) injection of GnRH agonists in lactating Holstein cows on the day of in vitro derived embryo transfer (ET) increases the number of accessory corpora lutea, progesterone concentrations and pregnancy rates compared to untreated controls. Average days in lactation were 190.4 ± 133 d and body condition score was 3.37 ± 0.45. Recipients (n = 254) were allocated to one of three i.m. treatments on the day of ET: Control – 2.5 ml saline; Buserelin – 10 μg Buserelin acetate; Deslorelin – 750 μg Deslorelin acetate. Ultrasonography and blood samples were done on the day of and seven days after treatment. The first pregnancy diagnosis was performed between 30 - 40 days and the second between 60 - 80 days post ET. Percentages of pregnancy and cows with accessory CLs were analyzed as binomial distributions by the GENMOD procedure (SAS®). Progesterone concentrations were analyzed as time repeated measures by the MIXED procedure (SAS®). The proportion of cows with accessory CLs was greater in the Buserelin treatment compared to control (P = 0.0045) and Deslorelin (P < 0.0001). Total progesterone concentration was not influenced (P = 0.84) by treatments. The final pregnancy rate was not different (P = 0.32) between treatments. In conclusion, GnRH agonists did not improve pregnancy rates, under the present experimental conditions.