Conception rate according to antral follicle count and oestrus expression in Nelore cows submitted to timed artificial insemination

Abstract

Context Antral follicle count (AFC) has been related to bovine fertility and response to reproductive biotechnologies, but its relationship to oestrus expression during timed artificial insemination (TAI) is not known. Aims This study evaluated the relationship between the AFC and oestrus expression in regard to the conception rate in beef cows that received an ovulation synchronisation protocol for TAI. Methods Multiparous Nelore cows up to 40 days postpartum were evaluated by an ultrasound to determine the AFC, and were classified into low (≤15 follicles; n = 150), intermediate (≥19 and ≤26 follicles; n = 150) and high count (≥30 follicles; n = 150). AFC evaluation was performed on a random day of the oestrous cycle (Day 0). The animals received a conventional TAI protocol based on progesterone and oestradiol benzoate. On Day 8, the animals received cloprostenol, equine chorionic gonadotrophin and oestradiol cypionate, in addition to a painting in the sacrococcygeal region. On Day 10, TAI was performed, and oestrus expression was evaluated and classified as high, low or absent, according to the removal of paint. Pregnancy diagnosis was performed by ultrasound 30 days after TAI. The data were analysed using a generalised linear model and a binary logistic regression model (P < 0.05). Key results Regardless of AFC, a high proportion of cows showed high oestrus expression (low 61.3%; intermediate 67.3% and high 58.7%) at the end of the TAI protocol. The conception rate was influenced by AFC (low 69.3% vs high 56.7%; P = 0.04) and oestrus expression (high oestrus: 67.3% vs no oestrus: 45.4%; P = 0.003). In addition, an interaction (P = 0.008) between AFC and oestrus expression showed that low AFC cows and high oestrus expression had the highest conception rate to TAI. Conclusion AFC and oestrus expression classification influenced the conception rate of Nelore cows in the TAI programme. In addition, the interaction of AFC with oestrus expression revealed that the best conception rate was observed in females with low AFC that expressed high-intensity oestrus. Implications The associated assessment of AFC and oestrus expression represents a strategy to increase the conception rate in TAI programmes in cattle.