Increased antral follicle population and in vitro embryo production in pregnant Holstein

Abstract

This study used Holstein cattle to evaluate the following: I) the productive and reproductive characteristics of cows with low, intermediate and high antral follicle counts (AFCs) that were subjected to artificial insemination (AI) and comparison of AFC variability at the time of AI (nonpregnant) and at two time points during pregnancy (30 and 60 days), and II) whether the pregnancy status and different pregnancy periods in heifers improves the efficiency at in vitro embryo production (IVEP). In study I, 75 high-milk production cows with body condition scores (BCSs) of 2.75 to 4.75 and ages of 23 to 99 months were selected. On the day of estrus, AFCs (follicles ≥ 3 mm), BCS, body weight, and diameters of the dominant follicle, ovaries and the corpus luteum were evaluated. Posteriorly, AFC was monitored in pregnant cows at 30 days (n = 35) and at 60 days for comparison of AFC before pregnancy versus different periods. In study II, heifers (n = 9) with BCS of 2.5 to 3.5 and ages of 10 to 16 months were selected for ovum pick-up and an IVEP program before AI (nonpregnant) as well as at 0 to 30, 31 to 60, and > 60 days of pregnancy. Statistical analysis was performed using PROC GLM and binary logistic regression model (P ≤ 0.05). In study I, AFC was not associated with variations in productive and reproductive parameters. However, AFCs in the low group increased following pregnancy (AI: 14.82 ± 1.36, 30 days: 23.45 ± 2.31 and 60 days: 35.18 ± 3.17 follicles). AFCs increased from AI to 60 days in the intermediate group but did not vary among time points in the high group. AFCs varied among AFC groups in AI and at 30 days of pregnancy but not at 60 days. In study II, the mean of total oocytes (17.43 ± 4.52 vs. 41.67 ± 3.79) and viable oocytes (13.77 ± 3.63 vs. 30.56 ± 3.45) increased from AI (nonpregnant) to the first 30 days of pregnancy. The mean number of embryos produced increased during pregnancy and during the first 30 days of pregnancy (4.55 ± 0.75) compared to the nonpregnant period (1.39 ± 0.85). In conclusion, pregnancy positively influences AFC, and the greatest effect is noted in low count cows. In addition, the OPU at the time of pregnancy increased the efficiency of IVEP in heifers.