LAUSR

Forty-eight (427.4 ± 40.92) Hereford cross heifers were used to determine the relationship between different temperamental traits with blood parameters, levels of stress hormone and social interactions of beef cattle. The first day of the experiment, heifers were randomly distributed in two pens (24 hd/pen), and the temperament of each animal was evaluated using flight speed, chute movement score, and human and novel object reactivity tests. Each group of twenty-four heifers was placed in an observation pen (24 x 8 m) where social behaviors were recorded with video cameras and later analyzed. The second day, an open-field test was conducted on the seven calmest and seven most excitable heifers based on a temperament score developed based on the traits measured on day 1. Finally, on d 8 of the experiment, an ACTH challenge was conducted on the same seven calmest and seven most excitable heifers to assess HPA-axis reactivity. Blood samples were taken immediately prior and 60 and 120 minutes following the injection of exogenous ACTH to measure plasma cortisol and obtain a complete blood cell count. Animal’s exhibiting dominant behaviors had a greater level of plasma cortisol (P = 0.0435) and flight speed (P = 0.0371) than those with a balanced social status, while those with a balanced social status had a greater (P = 0.0115) white blood cells count than those heifers with a subordinate social profile. There was a strong positive correlation (P = 0.0094, R-square= 0.7386) between flight speed and plasma cortisol. The more excitable animals exhibited a blunted HPA-activity in response to administration of exogenous ACTH. These results show that there is a relationship between temperament, levels of stress hormones and social dominance, suggesting that temperament impacts the amount of stress individual animals experience as well as their health and social status.