Evaluation of Ovarian Response and Percentage of Gestation in Mexican Tropic'S Heifers Treated With Melengestrol Acetate

摘要

The aim of this study was to assess the ovarian response and the percentage of gestation in Mexican tropic's heifers treated with melengestrol acetate (MGA). The work took place in the municipality of Tzitzio, Michoacan, Mexico. Twenty-five, 43±4.6 months old heifers, weighting 312.72±25.78 kg, and recording 3.0±0.25 of body condition were feded with 0.5 mg of MGA pre-blended with 250 g of supplement through 21 days. At the end of the treatment the heifers ovaries were observed over ultrasonography daily until the ovulation time, and then four more times every 5 days to observe the corpus luteum development. The heifers were direct mated, and 88% of them revealed dominant follicle post-treatment, and had their ovulation on the fifth to tenth day, focused on the eighth day (72.7%). Most of them (95.5%) were pregnant after the mating; realizing that ovaric response of the heifers treated with MGA at a dose of 0.5 mg per day through 21 days standarize the estrous advent. Moreover, it shows that the ovum have the conditions to be fertilized. The MGA may be used as an important constituent to perform a strategy to achieve homogeneous calves lots in suitable times for production, thus contributing to the Mexican tropic's livestock reproductive parameters improvement.