This experiment was aimed at comparing two estrus induction protocols for cows in post partum period, using either GnRH and two-day artificial insemination (AI) or estradiol benzoate (EB) and fixed-time artificial insemination (TAI). A total of 250 suckled beef cows received a vaginal device containing 250mg of medroxyprogesterone acetate (MPA) and an injection of 5mg of EB intramuscularly (IM) on day 0. The vaginal device was removed on day 7. On day 6, cows were injected with 400IU eCG (IM) and 5mg prostaglandin analog (into vulvar submucosa) and calves were removed for 96 hours (h). After removing the vaginal devices (day 7), cows were divided in two groups. In the BioRep group (n=150), estrus detection was carried out twice a day during 48h and the animals were inseminated 12h after detection. Cows which were not detected in estrus received 100mg of GnRH IM and were inseminated 16 to 18h later. In EB group, cows were injected IM with 1mg of EB on day 8 and were inseminated on day 9 without estrus detection. The pregnancy rate was higher (P<0.01) in the BioRep group (54.7%) than in the EB group (33.3%). In suckled cows, two days of estrus detection associated to fixed-time insemination using GnRH to induce ovulation allowed the attainment of higher pregnancies rates than exclusively TAI using EB.
post partum; insemination; estrous induction; GnRH; estradiol
