Potential of sensor-derived estrus traits for genetic selection in dairy cattle

Genetic improvement of fertility in dairy cattle remains a significant challenge due to the complex interplay between reproductive and environmental factors resulting in low heritability traits. Recent advancements in sensor technologies have allowed for the assessment of estrus-related traits as indicators of fertility. Three sensor-derived estrus traits previously associated with fertility outcomes include estrus duration (ED), maximum estrus intensity (MEI), and the interval from calving to first estrus (CTFE). The objectives of this study were to estimate the genetic parameters of ED, MEI, and CTFE in Holsteins, to assess the reliability of EBVs, to evaluate the inclusion of genomic information, and to estimate breeding value correlations with economically important traits. Phenotypes were derived from activity-monitoring collars (CowScout, GEA) between 2020 and 2023 from a single farm in Slovakia. After editing, 8,363, 8,092, and 2,909 records on 2,390, 2,360, and 2,147 cows were available for analysis of ED, MEI, and CTFE, respectively. Heritability estimates for the traits were low to moderate, with values of 0.18 ± 0.02 for MEI, 0.16 ± 0.02 for ED, and 0.07 ± 0.03 for CTFE. Repeatability across lactations was 0.34 ± 0.03 for CTFE, but no significant permanent environmental effect was found across lactation for MEI and ED. Repeatability within lactation was low for MEI (0.25 ± 0.02) and ED (0.19 ± 0.01). The average reliability of EBVs was moderate for phenotyped cows, with values of 0.32 ± 0.05 for CTFE and 0.48 ± 0.09 for MEI and ED. For sires with at least 10 daughters, EBV reliability ranged from 0.56 ± 0.11 for CTFE to 0.79 ± 0.13 for MEI and ED. Inclusion of genomic information did not greatly affect genetic parameters and resulted in marginal improvements to reliability of breeding values. Genetic correlations among estrus traits were moderate and favorable, indicating that better performance of 1 trait will correspond to improved performance in the other 2 traits. Breeding value correlations between estrus traits and economically important traits were generally favorable. These results suggest that sensor-derived estrus traits are heritable, with potential for more rapid progress in reproduction than currently evaluated traits. Future research should estimate proper genetic correlations between estrus traits and other economically important traits and expand datasets to enhance the genetic evaluations of these sensor-derived estrus traits.