113 Influence of antral follicles count on conception rate in Holstein cows and antral follicles count variation on insemination day and on pregnancy Day 30 and 60

Several studies have indicated the population of antral follicles or count of antral follicles (AFC) as one of the main factors that influence the efficiency of reproductive biotechniques and its use as a marker of fertility. In this context, knowing the factors that interfere with or are influenced by this parameter is of crucial importance. Thus, the present study aimed (1) to determine the influence, in high-producing Holstein cows, of low, intermediate, and high AFC on the conception rate to AI, and (2) to evaluate if AFC shows variation at AI moment and in relation to 2 different moments of the gestation (30 and 60 days). In the first (n=95) and second (n=54) experiment, high-producing Holstein cows with a body condition score 2.5-4.5, aged 23-99 months, and maintained in a freestall system were inseminated. Using frozen semen from a single bull and performed by a single technician, the insemination was performed after detection of spontaneous estrus or induction with 25mg of dinoprost tromethamine IM. To determine AFC (follicles ≥2mm), the ovaries of each animal were examined by ultrasound at the time of AI at 30 and 60 days of pregnancy. The pregnancy diagnosis was performed by ultrasound 30 days after AI. In the second experiment, 54 females considered pregnant on the 30-day examination had the AFC reassessed 30 days later (60 days of gestation) to determine the variation in the number of follicles. In the first study, cows were divided into low (≤35 follicles, n=30), intermediate (≥40 and ≤55 follicles, n=30), and high (≥60 follicles, n=30 cows) according to the AFC quartiles (Q1, Q2, and Q3). The AFC was analysed by ANOVA followed by the Tukey's test and the conception rate by the Chi-squared test. In the second study, the AFC was compared between day of AI (considered nonpregnant), 30 and 60 days of pregnancy by repeated-measures using the generalized linear model (P ≤ 0.05). In the first study, the number of antral follicles was different (P