Adding behavior traits to select for heat tolerance in dairy cattle

Abstract

The increase in periods of heat waves leads to an increase in heat stress events in dairy cattle leading to welfare, production losses and health issues. However, the low frequency of milk recording data makes genetic evaluation for heat tolerance still a challenge. A possible solution could be to add behavior data captured through sensors which are recorded permanently, mostly reported on a daily basis. The objective of this study was to evaluate the potential gain of adding behavior traits as proxies for genetic evaluation of heat tolerance. Behavior traits including activity time (ACT), rumination time (RUM) and eating time (EAT) were recorded for 453 Holstein cows equipped with SenseHubTM collars from October 2019 to July 2022 in 6 herd located in the Walloon Region of Belgium. A multi-trait reaction norm model based on separate temperature and humidity index (THI) thresholds was used. Results showed that behavior traits present not only interesting characteristics for genetic evaluation of heat tolerance but also for heat stress detection in farms. Indeed, sensors allow to record behavior for all events of heat stress in lactating and nonlactating animals. Moderate heritability values were also found for the behavior traits (0.14 for ACT, 0.19 for RUM and 0.12 for EAT) and a high ratio between the general and thermotolerance additive genetic variances was obtained. In addition, positive correlations of thermotolerance for ACT and EAT with thermotolerance for milk production (fat- and protein-corrected milk) (0.45 and 0.28 respectively) and negative genetic correlations of thermotolerance for ACT with somatic cells (somatic cell score (SCS)) (−0.39) were estimated. The genetic correlation matrix allows to explain a high part of the variation for the reaction to heat stress of 2 economical traits (fat- and protein-corrected milk (FPCM): 59% and somatic cell score: 31%) based on behavior data. Based on these results, behavior traits could be used to assess heat stress in nonlactating cattle for which the number of genetic evaluations for heat tolerance are still limited.