Avaliação crítica da adoção de protocolos hormonais sobre o desempenho reprodutivo de fêmeas zebuínas

Abstract

The experiments were conducted in five different farms located in Minas Gerais State, with particular management according to the use of breeding season, suckling restriction and artificial insemination. The animals were divided into categories (heifer, non-lactating and lactating cows) and their reproductive status were evaluated by rectal palpation and ultrasonography before trial. Cyclic cows were treated with 0,212mg prostaglandin F2 administered in the vulva submucosa. Prostaglandin treatment was repeated on animals not showing estrus signs. Anestrus cows were treated with 8-days intravaginal progesterone release device associated to a 1mg of estradiol benzoate and estradiol cipionate injection at the placement and withdrawal of intravaginal device, respectively. Atificial insemination was performed 12 hours after estrus detection that was monitored by twice or three times a day, during 30 min, with or without teaser bulls depending on the farm. The pregnancy was checked between days 45 to 60 after artificial insemination and at the end of the experimental period. Prostaglandin F2 treatment presented good synchronization rates (66.7 to 100.0%) and pregnancy rates ranged from 48.5 to 83.3%. The results for anestrus animals treatment had larger variation among farms. Estrus rate for heifers ranged from 80.0 to 92.3% and pregnancy rates from 33.3 to 61.5%. For lactating cows the estrus rate ranged from 31.9% to 82.0% and pregnancy rate from 4.3 to 44.0%. After progesterone and estradiol protocols the number of cows returning to estrus was different among farms, probably due the differences on metabolic status and body condition score. Hormone protocols can anticipate estrus and gestation during breeding season in cows that are able to respond to the treatment, and promote artificial insemination in farms that normally do not use this technique