Anticipation of estrus and ovulation in Nelore heifers with low antral follicle count.

This study aimed to establish the relationship between antral follicle count (AFC), the time of puberty, and ovarian response in Nelore heifers subjected to timed-AI (TAI) protocols. Prepubescent Nelore heifers (Bos indicus; n = 30) were examined by transrectal ultrasound and videos of the ovaries were recorded for later CFA (? 3 mm). After AFC, heifers were divided into 2 groups, low and high AFC and then further ultrasonic ovarian assessments were performed to determine the onset of puberty. Once puberty was established in all heifers, they were submitted to an FTAI protocol. There were no differences (P > 0.1) between groups on the time of puberty, ovulation rate, the proportion of heifers that expressed estrus, and on preovulatory follicle diameter. However, heifers with low AFC had a smaller ovarian area in the prepubertal period (4.36 ± 0.3 vs. 5.65 ± 0.2 cm2) and, in the FTAI, they had the moment of estrus (48 ± 0.0 vs. 58.5 ± 3.1 h) and earlier ovulation (60 ± 1.8 vs. 72.6 ± 4.7 h) compared to heifers with high AFC (P 0,1) entre os grupos na idade à puberdade, na taxa de ovulação, na proporção de novilhas que expressaram estro e no diâmetro do folículo pré-ovulatório. No entanto, novilhas com baixa CFA apresentaram menor área ovariana no período prépúbere (4,36 ± 0,3 vs. 5,65 ± 0,2 cm2) e, na IATF, tiveram o momento do estro (48 ± 0,0 x 58,5 ± 3,1 h) e ovulação antecipados (60 ± 1,8 vs. 72,6 ± 4,7 h) em comparação com novilhas com alta CFA (P 0.1) entre los grupos en el momento de la pubertad, la tasa de ovulación, la proporción de vaquillas que expresaron celo y el diámetro del folículo preovulatorio. Sin embargo, las vaquillas con AFC bajo tuvieron menor área ovárica en el período prepuberal (4,36 ± 0,3 x 5,65 ± 0,2 cm2) y, en el IATF, tuvieron el momento del estro (48 ± 0,0 x 58,5 ± 3,1 h) y ovulación más temprana (60 ± 1,8 x 72,6 ± 4,7 h) en comparación con novillas con AFC alto (P < 0,05). Además, las vaquillas en el grupo de AFC bajo tuvieron una tasa de preñez más alta (P = 0.05) (76.9 %, 10/13) que el grupo de AFC alto (29.4 %, 5/17). Las vaquillas con AFC bajo tuvieron el momento de ovulación anticipado y mayor preñez por IA en comparación con las vaquillas con AFC alto