Aplicação de uma segunda dose de prostaglandina F2α em protocolo de inseminação artificial em tempo fixo para vacas nelore

Abstract

The objective of this study was to evaluate the efficiency of two applications of prostaglandin F2α (PGF2α) in a protocol of artificial insemination at fixed time (IATF) for Nellore cows. A total of 252 adult Nelore cows, weighing 450 kg on average, were previously evaluated for their reproductive status, clinical evaluation, body condition and ovarian activity by means of ultrasound examination. The animals were randomly assigned to two groups and submitted to the hormonal protocol. On day 0 (D0) of the protocol, all cows received a single intravaginal implant of 1 mg of progesterone (P4) and 2 mg of intramuscular estradiol benzoate (IM), with: G1 control group, (n = 116) cows receiving 150 μg of a synthetic analogue of PGF2α, 300UI of equine chorionic gonadotrophin (eCG) and 0.5mg of estradiol cypionate, all applied via IM in D9; G2 (n = 136): cows receiving 150μg of a synthetic analogue of PGF2α in D7, a second application of PGF2α, 300UI of eCG and 0.5mg of estradiol cypionate in the D9 of the protocol, all via IM. Fifty-two hours after withdrawal of the P4 implant the IATF was performed in the animals of the two groups. The following variables were evaluated: Gestation rate and late embryonic loss, Intensity of estrus of beef cows on gestation rate at 30 and 60 days, Gestation rate of beef cows according to body condition score submitted to one and two doses of PGF2α in IATF protocol. The data were submitted to the normality evaluation by the Shapiro Willk test. For the quantitative variables that presented normal distribution, Variance Analysis (ANOVA) was performed. Wilcoxon- Mann-Whitney test was used for the variables that did not present normal behavior. The chi-square test (X2) was used for gestation rate, because it was a binary variable. The 5% level of significance was adopted for all tests. There was no difference in the gestation rate at 30 and 60 days between treatments, with a mean of 50% for G1 and 39.23% for G2, for DG 60, 46.72% for G1 and 39.23% for G2. Late embryonic loss between 30 and 60 days of gestation was 1.87% for G1 and 0% for G2. There was no difference in estrus intensity on the gestation rate. There was no effect of the body condition score assessed between the groups on the gestation rate. The use of an additional dose of PGF2α in D7 of the IATF protocol for Nelore cows did not improve the efficiency of this protocol and its use was not indicated.