Indução da ovulação em vacas de corte ganhando e perdendo peso durante o período pós-parto

Abstract

The aim of this study was to compare the efficiency of a hormonal treatment associate to 96-hour calf remove with a weaning, in animals with different forage availability and weight gain, as well to assess its cost-benefit in the fertility of beef cows. Three hundred and ten cows, which were between 50 and 70 days postpartum were used (190 Angus and 120 Charolais) raised in Tupanciretã, in the central region of the State of Rio Grande do Sul. They were classified and distributed according to their body condition (1 to 5) into six groups. The groups A2, A5, B2 e B5 were formed, respectively, by 53, 49, 53 e 55 cows. Had more (A2 e A5) and less (B2 e B5) forage availability during the time between the delivery and the beginning of the treatment. They received (Day 0) 2mg of stradiol benzoate (A2 e B2) or 5mg of stradiol benzoate (A5 e B5), and intra-vaginal implant (CIDR) with progesterone (P4). Six days after (Day 6), received 1000 UI of equine corionic gonadotropin (eCG). On the following day (Day 7), the CIDR was withdrawn and initiated the calves wean for 96 hours. The groups AD e BD were formed by 52 and 48 cows, which had, respectively, more and less forage availability, during the time between the delivery and the beginning of the treatment. They were definitely separated from their calves on Day 7. All the cows that showed oestrus was artificialy inseminated (AI) between Days 7 and 17. After that, they remained with bulls (12%) up to Day 67. After 54 days (Day 60), an pregnancy clinical diagnosis, and ultrasonographic, was made in order to see the cows that conceived in the oestrus after the treatment and, on Day 127, a second pregnancy diagnosis, was made so that the final pregnancy rate of the experiment could be identified. The data was analysed by Chi-square analysis and it showed that there was no significant difference in the pregnancy rates between the groups with diferent forage availability, carrying at regrouping of the cows according your weight gain. There was no difference between stradiol benzoate doses (2 and 5 mg), consequently, was regrouped the treatment A2 and A5 in ATH and B2 and B5 in BTH. The Aberdeen Angus breed obtain bigger pregnancy rates of first postpartum oestrus as Charolais breed (P=0.0013). The group GTH presented smaller pregnancy rates of first postpartum oestrus (P=0.0021) and the end pregnancy rates (P=0.0001) as the group GDD. At once in the cows that losses weight, the PTH group presented end pregnancy rates as PDD group (P=0.0349). The cows with prepartum body condition number 4 presented bigger pregnancy rates of first postpartum oestrus (P=0.0008) as the cows with body condition number 3.The hormonal treatment with 2 mg of stradiol benzoate is so efficient as to 5 mg in the induction of ovulation in beef cows during pospartum. The weaning is more efficient and possible economic that the hormonal treatment used. The different forage availability during pospartum no direct determine the weight gain of the cows. The cows that lose weight more slowly answer form the weaning as cows that gain weight in the pospartum. The cows with body condition number 3, in prepartum, more slowly answer form the treatments as cows with body condition number 4.