130 Increased antral follicle population at 60 days of gestation in Holstein cows with low antral follicle count

Abstract

The antral follicle count (AFC) has been pointed out as one of the main factors that influence the efficiency of reproductive biotechniques. Thus, AFC is considered a fertility marker, which has high repeatability in the same animal. The objective of this study was to evaluate AFC in cows at AI (nonpregnant) and at two moments of gestation (30 and 60 days). For this, 35 pregnant cows, aged 23 to 99 months, confined in a freestall system, kept in the same environmental conditions (24°46'28”S, 49°56'42”W) and under the same feeding conditions, were selected for this study. The same technician performed the AI of the females, after detection of natural or induced oestrus, with 25mg of Dinoprost (Lutalyse) intramuscularly (IM). We established AFC (antral follicles ≥3mm diameter) using a convex intravaginal transducer at the time of AI and at 30 and 60 days of pregnancy. Females were distributed in groups of low (≤18 follicles, n=11), intermediate (≥24 and ≤28 follicles, n=11), or high AFC (≥30 follicles, n=13). Data were analysed using a generalized linear mixed model (Minitab version 18.1), with significance declared at P ≤ 0.05. In the low AFC group, there was an increase in the mean number of antral follicles in relation to gestation, presenting 14.82±1.36 at the time of AI and 23.45±2.31 and 35.18±3.17 at 30 and 60 days of pregnancy, respectively (P<0.0001). Similarly, the intermediate group presented an increase in mean AFC, from 24.64±0.76 at the time of AI and 29.27±3.32 at 30 days to 43.36±5.91 at 60 days of gestation (P=0.001). There was no difference in the high AFC group at different moments, as these presented 41.92±3.50 at the time of AI, 38.31±3.96 at 30 days, and 50.92±5.49 at 60 days of pregnancy. Although mean AFCs differed (P<0.0001) between the low, intermediate, and high AFC groups at time of AI and at 30 days of gestation, there were no differences in AFC between the three groups at 60 days of gestation (P=0.329). In conclusion, low AFC females presented an increase in the number of antral follicles at gestation moments 30 and 60 days from AI. This finding reinforces the strategy of using this category more efficiently for ovum pickup at the beginning of gestation.