Controle farmacológico da onda folicular em vacas Nelore associando acetato de melengestrol, prostaglandina e gonadorelina

Abstract

The objective of this study was to evaluate the pregnancy rate, follicular diameter and serum level of melengestrol acetate (MGA) correlating them, and comparing drug costs and their impact on the cost of pregnancies in two groups of lactating, multiparous cows, artificially inseminated at fixed time (AIFT), in two trials, with the animals divided in two groups (G). In G1, n = 30 (trial I) was applied, GnRH analogue (100 mg Gonadorelin) on day one, considered the start of treatment, prostaglandin analogue (75 g D-cloprostenol) on day seven, the second application of GnRH analogues in the day nine. In G2, n = 28 (trial I) was given similar treatment as G1 plus MGA in mineral mixture (0.05 mg MGA / cow / day) between days one and seven. The animals in trial II were also randomly divided into two groups (G1, n = 40 and G2 n = 41), receiving pre-treatment with MGA (0.5 mg / day) for fourteen (G1) or seven (G2) days. Thereafter it was used GnRH (100g of gonadorelin) on day one(d1); Prostaglandin (75 mg D-cloprostenol) on day seven (d7), and a second dose of GnRH (100g gonadorelin) on day nine (d9), when the inseminations were performed. In trial I, the diameters of ovarian follicles measured 1.04 ± 0.37 and 0.98 ± 0.35 cm in d1, 1.00 ± 0.28 and 1.01 ± 0.40 in d7, and 19 ± 0.32 and 1.12 ± 0.30 cm in d9, (P> 0.05); pregnancy rates were 26.66% and 28.57% after TAI, 63.33% and 64 28% after using cleanup bulls (P> 0.05), respectively, for G1 and G2. In trial II, the follicular diameter measured 1.08 ± 0.31 and 0.94 ± 0.23 cm (P< 0.05); pregnant rate of 24% and 22% (P> 0.05), respectively, G1 and G2. In trial I, concentration of MGA was 0.12 ± 0.20 and 0.0 ng / ml (P> 0.05) and in trial II 0.03 ± 0.06 and 0.07 ± 0.02 ng / ml (P< 0.05), respectively, for G1 and G2. The total drug cost in the first trial was US$138.00 and US$177.80, and in the second trial of US$332.10 and US$254.00, respectively, for G1 and G2. Spending on material of consumption peranimal and per pregnancy in the first trial, was of US$11,42, US$13.23, US$38.06 and US$46.32, and in the second trial of US$15.01, US$13.23, US$35.95 e US$31.04, respectively, for G1 and G2. Consumption of MGA for seven to 14 days did not affect the pregnant rate in none of the experimental groups. However, the follicles showed larger diameters when MGA was fed for 14 days, showing a uniform serum level throughout the period of consumption, suggesting a positive correlation between follicular diameter and consumption of MGA for periods longer than seven days. The economic efficiency of production systems can be greatly increased by reducing spending on material consumption by increasing pregnant rates that can be obtained with the proposed protocols.