Relationship between follicular diameter, commercial estrus breeding indicator and pregnancy rate in beef cattle

The objective of this study was to evaluate pregnancy rate from fixed-time artificial insemination (FTAI) performed in cows related to an estrus scores breeding indicator and measurement of preovulatory follicular diameter (POF). Forty-three crossbred Zebu cattle of reproductive age, 28-days postpartum. It was started the ovulation synchronization protocol, and eight days after the auxiliary tool for the detection of estrus (Estrotect®) was inserted. POF was measured by transrectal ultrasonographic examination. For the FTAI protocol, the animals were allocated into four groups based on POF. Group 1 (POF ≥15 mm) was inseminated immediately at ultrasound; group 2 (POF = 13–14.9 mm) 6 h later; group 3 (POF = 10–12.9 mm) 24 h; and group 4 (POF = 8–10 mm or <8 mm) 30 h. Total pregnancy rate was 72.9% (group 1: 20.1%; group 2: 20.9%; group 3: 20.9% and group 4: 16.3%). Follicles with a diameter of 7.25 mm were observed for animals with a score of 1, 11.0 mm for 2, 11.9 mm for 3, and 14.5 mm for 4. The estrus breeding indicator is a safe and practical tool, used to facilitate the reproductive management of beef cattle during the IATF protocol.