Influence of testosterone on the docility of German Simmental and Charolais heifers during behavior tests

In beef cows, docility is important for animal welfare reasons, the farmer's and veterinarian's safety as well as for economic reasons. The hormone testosterone is often mentioned in the context with aggressions and docility. The present study tested the hypothesis that higher testosterone levels in beef cows are associated with more aggressive behavior and lower docility during behavior tests. German Simmental (beef) (n=21) and Charolais heifers (n=20) were subjected with one repetition to a chute test as well as a separation and restraint test. Heart rate, thermal images of the eye, saliva cortisol as well as saliva testosterone were collected along with behavioral parameters during the tests. For all physiological and most of the behavioral parameters significant breed differences were detected. Charolais heifers (0.10 ± 0.01 ng/ml saliva) had considerably higher testosterone levels compared with Simmental heifers (0.04 ± 0.01 ng/ml; P=0.0001). Interestingly, the Charolais heifers expressed a higher docility, so across breeds higher levels of testosterone are associated with higher docility. However, all the parameters presumably linked to stress (heart rate, eye temperature, cortisol levels) generally showed stronger correlations to behavior traits than testosterone (e.g., trait "time in corner" - testosterone: r=0.25 vs. cortisol: r=-0.43 (Fisher's r-to-z: P=0.0985); eye temperature: r=-0.65; (P=0.0005); heart rate: r=-0.60 (P=0.003)). Eye temperature correlated with both heart rate (r=0.68) and cortisol levels (r=0.62; both P<0.0001). Therefore, eye temperature more so than testosterone appears to be a suitable indicator of stress, and as such also an, albeit incomplete, indicator of docility in cattle.