Relationships Between Antral Follicle Numbers and Postpartum Interval in Brahman Females

The purpose of this study was to correlate ovarian antral follicle count (AFC) on d 28 postpartum with postpartum interval (PPI) and AFC on d 8 post-estrus in Brahman cows. Three-dimensional ultrasonography was performed on multiparous (n = 47) and primiparous cows (n = 20) on d 28 postpartum and on d 8 post-estrus. Follicles were evaluated to determine numbers of total, small (≤ 17 mm³), medium (17 mm³ to 67 mm³), and large follicles (≥ 67 mm³) on each ovary. Estrus was detected using heat-check bulls. Cows with AFC ≥ ½ SD above the mean were high, those within ½ SD of the mean were intermediate, and those ≥ ½ SD below the mean were low. Classes of AFC for total follicles included low (L ≤ 73), intermediate (74 ≤ I ≤ 112), and high (H ≥ 113). Classes of AFC for small follicles included low (L ≤ 55), intermediate (56 ≤ I ≤ 87), and high (H ≥ 88). Classes of AFC for medium follicles included low (L ≤ 13), intermediate (14 ≤ I ≤ 23), and high (H ≥ 24). Classes of AFC for large follicles included low (L ≤ 2), intermediate (3 ≤ I ≤ 4), and high (H ≥ 5). The PROC MIXED procedure of SAS was used to analyze classes of AFC. The PPI differed among classes of total (P < 0.01; L = 76.2 ± 6.0, I = 61.7 ± 4.5, H = 43.8 ± 6.5), small (P < 0.01; L = 74.3 ± 5.6, I = 64.6 ± 4.8, H = 42.9 ± 5.9), and medium AFC (P = 0.04; L = 72.3 ± 5.9, I = 59.3 ± 5.8, H = 52.1 ± 5.8). The PROC REG procedure of SAS was used to analyze AFC and PPI. As total AFC on d 28 postpartum increased, PPI decreased (P < 0.01, Adj.R² = 0.13). Total AFC on d 8 post-estrus was positively affected by total AFC on d 28 postpartum (P < 0.01, Adj.R² = 0.66). These results suggest that: a) populations of total, small, and medium follicles in the postpartum period predict PPI in Brahman females and b) total AFC in Brahman females are consistent