The purpose of this experiment was to assess the efficiency of hormonal treatments on the fertility of beef cows raised extensively on the west border region of Rio Grande do Sul, Brazil. A hundred and forty-three cows (Hereford and Crossing breeds) which were between 50 and 70 days after delivery were used and, after being classified according to their body condition (BC), varying from 1 to 5, they were separated into three groups. The SEMED group had 50 cows, which received (day 0) 500mg of bovine somatotropin (bST), 5mg of benzoate of estradiol and an intravaginal pessary containing 250mg of medroxiprogesteron acetate (MAP) and, six days later, (day 6), 500UI of equine chorionic gonadotropin (eCG). By the time the pessaries were withdrawn, the calves were totally separated from their mothers for 96 hours. In the EMED group, which had 48 cows, a treatment similar to the previous one was adopted, differing only in the non-use of somatotropin. In the CONTROL group, 43 cows were only separated from their calves for 96 hours. Right after the vaginal pessaries withdrawal and the separation from the calves, the cows were placed in an pasture with bulls (1:10). After 53 days, a pregnancy diagnosis via rectal palpation and ultrasonography was done to detect the cows that had conceived in the estrous subsequent to the treatment. Pregnancy rates of 11.1%, 38.0% and 56.2% were obtained for the groups CONTROL, SEMED e EMED respectively, whose differences were significant (p<0.0001) among the groups. In the SEMED group the cows BC interferred in the treatment, because a superiority in the pregnancy rates of cows with BC 3 was observed when compared to cows with BC 2. This difference was not verified in the other groups. The results also showed that the treatments had a different result for cows with BC 2, with pregnancy percentages of 12.5, 32.2 and 55.5 for the groups CONTROL, SEMED and EMED (SEMED vs CONTROL= p<0.01; SEMED vs EMED = p<0.01; CONTROL vs EMED = p<0.0001). The pregnancy rates of cows with BC 3 were of 10.5, 50 and 55% respectively for the groups CONTROL, SEMED and EMED and they indicated a difference of (p<0.0001) between both groups and the control group. The results evidenced that a treatment without the use of somatotropin, given to the EMED group, can be adopted successfully either in cows with BC 2 or in cows with BC 3, which is different from the treatment used in the SEMED group because it was efficient only with cows with BC 3.
post-partum interval; estrous cycle induction; beef cows
