Efeito do uso da inseminação artificial em tempo fixo e de sistema automático de detecção de estro na eficiência reprodutiva de rebanho leiteiro

Abstract

The resumption of ovarian activity and the efficient detection of estrus during the postpartum period are critical to the reproductive performance of dairy cows. However, metabolic, productive, reproductive, and health-related factors can influence both the behavioral manifestation of estrus and the conception rate. In this context, automated activity monitoring systems have been used as auxiliary tools in reproductive management. This thesis was developed aiming to investigate factors associated with the conception rate in Girolando cows in response to fixed-time artificial insemination (TAI), as well as to evaluate the association between automated estrus detection and the resumption of ovarian activity in Holstein cows in intensive dairy production systems. In the first study, factors associated with pregnancy after artificial insemination (P/TAI) were evaluated. Moderate/Strong estrus was associated with a higher probability of P/TAI, with cows being 2.11 times more likely to become pregnant compared to those with Absent/Weak estrus (P = 0.004). Parity also influenced P/TAI: second-lactation cows were 2.89 times more likely to conceive (P = 0.003). The season was also associated with the outcome, with a lower probability of P/TAI during the Summer compared to Winter (P = 0.032). Semen type and milk production showed no significant association with P/TAI. In the second study, the occurrence of ovulation and estrus events detected by automated activity monitoring were evaluated up to 56 days into lactation. The body condition score was associated with ovarian activity, while the locomotion score was not significantly associated with ovarian activity or estrus detection. During this period, 88.9% of the cows exhibited at least one ovulation, while 80% exhibited at least one estrus event detected by the system. Silent ovulations were observed in 13.7% of the cows, and a moderate positive correlation was found between the number of ovulations and the number of detected estrus events. In conclusion, the intensity of estrus, parity, and season of the year should be considered when interpreting the reproductive performance of dairy cows in the postpartum period. In addition, automated activity monitoring is effective in helping to identify the resumption of ovarian activity, especially when an estrus alert is emitted, although it does not completely replace ultrasound evaluation given the occurrence of silent ovulations.