Regrouping induces anhedonia-like responses in dairy heifers

Abstract

Regrouping (i.e., mixing individuals to form a new social group) is common on dairy farms. The practice is known to be stressful, but how cattle react emotionally to this stressor is still poorly understood. We studied whether heifers experience anhedonia (i.e., the reduced ability to experience pleasure) following regrouping by comparing their use of a mechanical brush before and after regrouping. Heifers reduced their use of the brush 8 h after regrouping, suggesting that they were experiencing anhedonia. This method shows promise for assessing affective states when animals are subjected to routine stressors. Highlights• Regrouping is a stressful experience for cattle • Reduced ability to experience pleasure (anhedonia) indicates negative mood state • We measured changes in brush use to assess anhedonia in 6-mo-old heifers • Regrouping resulted in reduced brush use, indicative of low mood Animal Welfare Program, Faculty of Land and Food Systems,

Postpartum Stressors Cause a Reduction in Mechanical Brush Use in Dairy Cows

“…Experiment 1 did not aim at disentangling which specific stressors were affecting cows. In contrast with previous results showing a reduction in brush use only on the day of social mixing [ 10 ], the current study also found that cows changed their brush use for weeks following parturition. This suggests that post-partum stressors may in fact induce more severe welfare issues than those observed after social mixing alone.…”

“…One limitation of our study is that brush use was not consistent prepartum; the progressive decrease in latency and increase in brush use over the four-week period suggests that cows were still learning to use the brush and getting used to the testing routine. This result is consistent with previous reports, indicating that cows need time to master the use of the brush [ 22 ], and need many pre-testing sessions to obtain consistent measures when the brush is provided for limited periods [ 10 ]. One challenge in the current study is that cows were tested alone, and this may increase the time required to learn to use the brush effectively (most animals used it on the head and the neck before discovering it could be used on the back).…”

“…The decline in motivation and use of the mechanical brush after parturition and separation from the calf are consistent with previous results indicating that dairy cattle reduce their use of a mechanical brush when experiencing negative affective states [ 10 ] and health issues [ 8 , 12 , 13 ]. However, contrasting results exist.…”

“…Reductions in these types of behaviors have been used to identify dairy cows that are at increased risk for social stress or disease and thus compromised welfare. For instance, accumulated evidence suggests that cows reduce their use of a mechanical brush, a resource that they are highly motivated to access [ 9 ], when experiencing known stressful events [ 10 , 11 ] and negative health events [ 8 , 12 , 13 ]. Overall, these results are consistent with the idea that brushing is rewarding and that the expression of self-grooming behaviors (using a mechanical brush) generally drops in response to stressors.…”

Pessimistic dairy calves are more vulnerable to pain-induced anhedonia

“…nonfood rewards) may allow stronger inferences. For instance, we recently found that weaned calves reduce their use of a mechanical brush after social mixing [39].…”