Hormonal reduction in <i>Ovsynch</i> protocol to artificial insemination in fixed time at Nelore females

Abstract

The aim of this study was to evaluate the effect of hormonal reduction in Ovsynch protocol upon the diameter of the largest follicle at the end of the treatment and pregnancy rate in Nelore cows submitted to fixed time artificial insemination (FTAI), as well as to assess the influence of inseminator and
the existence of previous parturitions on pregnancy rate. A total of 176 Nelore females formed the treatments T1 (50µg Fertirelin D0, 530µg sodium cloprostenol D7 and 50µg Fertirelin D9; n = 91) and T2 (25µg Fertirelin D0, 265µg sodium cloprostenol D7 and 25µg Fertireline D9; n=85). The obtained data were compared trough the chi-square test to pregnancy rate and the size of the ovulatory follicle was compared using ANOVA. The pregnancy rates and the diameter of the largest follicle were 29.67% and 27.05%; 11 ± 2.84 and 11 ± 2.68 to T1 and T2, respectively. Results were not statistically different (P > 0.05) on comparison between groups. Inseminators and existence of previous parturitions showed no significant influence upon the pregnancy rate after FTAI. It was concluded that 50% of reduction on usually Ovsynch hormonal doses protocol did not interfere with pregnancy rate and largest follicle diameter in Nelore female, despite of parity of the cow or inseminator.