Eficiência reprodutiva em programas de inseminação artificial em tempo fixo (IATF) de rebanho Nelore: Análise comparativa do triênio (2023-2026)

Abstract

Reproductive efficiency in beef cattle is determined by the complex interaction between genetics, health, hormonal protocols, and nutritional management. This study analyzed the production indicators of 3,318 beef cows at Farms A and B over three consecutive breeding seasons (2023/24 to 2025/26), subjected to up to three FTAI (Fixed-Time Artificial Insemination) services. The results confirm Body Condition Score (BCS) as the primary biological predictor of fertility: scores below 2.50 (1-5 scale) compromised LH pulsatility and embryonic viability, increasing the effective cost per semen dose due to a lower service rate in the first FTAI. At Farm A, an increase in average BCS from 2.29 to 2.48 in the 2025/26 season resulted in a 9.7 percentage point gain in the final pregnancy rate (64.3% to 74.0%). Conversely, at Farm B, the regression of body condition (2.42 to 2.35) was associated with a sharp decline in fertility (86.1% to 59.9%). The correlation between maternal BCS and progeny performance proved equally critical: calves from dams with BCS ≥ 2.40 showed an adjusted 205-day weaning weight up to 45 kg higher, with an estimated economic impact of R$ 717.30 per calf. Notably, the decrease in average weaning weight was more pronounced among primiparous cows, a category that demonstrated higher sensitivity to negative energy balance. To optimize reproductive turnover, the use of Doppler ultrasonography allowed for a shorter breeding season by enabling three resynchronizations with an 8-day reduction in each cycle (24 days in total). The results ratify the need for systematic BCS monitoring every 14-21 days and stratified nutritional planning with supplementation during the dry-to-wet season transition to maximize the technical and economic efficiency of cow-calf operations