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

The objective of this meta-analysis was to evaluate the association of estrus detection within the voluntary waiting period (VWP) using automated activity monitoring (AAM) systems with reproductive performance in lactating Holstein cows. A comprehensive literature search was conducted in PubMed, ScienceDirect and Google Scholar using specific search terms. Inclusion criteria focused on studies that assessed estrus detection within the VWP using AAM systems. Six manuscripts involving 8,621 cows were included. Reproductive outcomes of interest were: (1) the proportion of cows inseminated at first service upon estrus detection detected by an AAM system; (2) pregnancy per artificial insemination (AI) at first service; (3) the proportion of cows pregnant within 150 DIM. Cows were classified based on the number of automated estrus alerts (AEA) within the VWP into 2 groups: (1) no estrus alert (EstrusNo); (2) at least one estrus alert (EstrusYes). Statistical analyses were conducted using MedCalc, incorporating 7 experimental groups from the selected manuscripts. The overall proportion of cows without estrus detection within the VWP was 36.6% (95% CI: 24.4%-49.8%). Cows (n = 5,093) in the EstrusYes group had greater odds for receiving AI upon estrous detection at first service (odds ratio [OR] = 3.36; 95% CI 2.32-4.88) compared with cows (n = 2,631) in the EstrusNo group. Cows (n = 5,577) with estrus detection within the VWP had greater odds for conceiving at first service (OR = 1.59; 95% CI 1.27-1.98) compared with cows (n = 2,793) without estrus detection within the VWP. Cows (n = 5,637) with estrus detection within the VWP had greater odds for pregnancy within 150 DIM (OR = 1.75; 95% CI 1.54-1.99) compared with cows (n = 2,815) without estrus detection within the VWP. There was substantial heterogeneity among the experimental groups, except for the effect of estrus detection within the VWP on pregnancy within 150 DIM. In summary, cows with no AEA within the VWP cows had inferior reproductive performance compared with cows with AEA. Therefore, estrus detected by AAM systems within the VWP is an important predictor of reproductive performance.