Evaluation of the association between automated estrus alerts from activity monitoring systems in early lactation with reproductive performance in lactating Holstein cows: A meta-analysis.

Automated activity monitoring systems for detection of oestrus have become popular tools due to their acceptable accuracy in detecting oestrus and ovulation. In association, a concept of targeted reproductive management has emerged based on the identification of subgroups of cows with or without oestrus detection by automated activity monitoring during the voluntary waiting period, that may require or benefit from different management approaches to optimize performance and profitability. By implementing individual management of cows based on automated oestrus alerts, targeted reproductive management enhances overall herd performance more effectively than relying on a blanket approach for all cows. For instance, cows with oestrus detection within the voluntary waiting period had a greater probability of conception through artificial insemination (AI) at oestrus. These cows may benefit from a reproductive management approach with AI after oestrus detection, while minimizing hormonal interventions. Contrary, cows with no oestrus detection in the voluntary waiting period may require more intensive synchronization protocols to enhance fertility when managed with timed AI.

Several studies investigated these concepts, but since individual studies often focus on a limited number of herds with similar management practices, climatic and environmental conditions, and genetic background, the results may not be representative in general. To address this challenge, a meta-analysis was designed by the authors cited with the objective to evaluate the association of oestrus detection within the voluntary waiting period, using automated activity monitoring systems with reproductive performance in lactating Holstein cows.

A comprehensive literature search was conducted. The criteria included focused on studies that assessed oestrus detection within the voluntary waiting period using automated activity monitoring systems. More than 8 500 cows were involved. Reproductive outcomes of interest were: (1) the proportion of cows inseminated at first service upon oestrus detection detected by an activity monitoring system; (2) pregnancy per AI at first service; (3) the proportion of cows pregnant within 150 days-in-milk (DIM). Cows were classified based on the number of automated oestrus alerts within the voluntary waiting period into two groups: (1) no oestrus alert (Oestrus-No); (2) at least one oestrus alert (Oestrus-Yes).

The overall proportion of cows without oestrus detection within the voluntary waiting period was 36.6%. Cows (n = 5,093) in the Oestrus-Yes group had greater odds for receiving AI upon oestrous detection at first service compared with cows (n = 2,631) in the Oestrus-No group. Cows (n = 5,577) with oestrus detection within the voluntary waiting period had greater odds for conceiving at first service compared with cows (n = 2,793) without oestrus detection. Cows (n = 5,637) with oestrus detection within the voluntary waiting period had greater odds for pregnancy within 150 DIM compared with cows (n = 2,815) without oestrus detection. There was substantial heterogeneity among the experimental groups, except for the effect of oestrus detection within the voluntary waiting period on pregnancy within 150 DIM.

In summary, cows with no automated oestrus alerts within the voluntary waiting period had inferior reproductive performance compared with cows with automated oestrus alerts. Therefore, oestrus detected by automatic activity monitoring systems within the voluntary waiting period could be an important predictor of reproductive performance.