Attenuation of Stress Responses to Human Handling Through Habituation in Goats.

Goats raised on pastures are seldom handled except for purposes such as weighing and providing veterinary care. Regular positive interactions with human caretakers have been reported to attenuate fear and stress responses to routine human handling; however, this has not been adequately studied in meat goats. This experiment was conducted to determine the effects of habituation to handling on behavioral, physiological, and metabolomic responses in goats when subjected to routine handling. Seventy-two male (uncastrated) Spanish goats (6 mo; BW = 25.2 ± 0.37 kg) were randomly allocated to one of two treatment (Trt) groups: (i) regularly handled by stroking the back of each goat before feeding time for 90 days (handled: H) or (ii) not subjected to handling during the same period, but all other conditions were the same (non-handled: NH). After the 90-day habituation period, the goats were subjected to an arena test in the presence of an observer. Immediately after the test, the goats were subjected to routine veterinary exams that involved blood sampling (0 min) and measuring heart rate (HR), respiratory rate (RR), rectal temperature (RT), and body weight (BW). Blood samples were also collected after the veterinary exam (20 min) to determine physiological and metabolomic responses. Data from the arena test were analyzed using a Mann-Whitney U Test, and blood physiological responses were analyzed using MIXED procedures in SAS with sampling time (Time) as a repeated measure. Unpaired t-tests showed that the increase in BW was higher in the H goats (p < 0.01) compared to the NH goats over the 90 d habituation period. The approach distance from the observer (p < 0.05) and frequency of urination (p < 0.05) were greater in the NH goats during the arena test. HR (p < 0.01) and RR (p < 0.01) were higher in the NH group compared to the H group. Plasma cortisol concentrations were higher at 20 min than at 0 min (p < 0.05), while epinephrine (p < 0.05), metanephrine, normetanephrine, phenylethylamine, and 5-methoxytryptamine concentrations were higher (p < 0.05) in the NH goats than in the H goats. A targeted metabolomics analysis showed that six of the eight affected amino acids were lower (p < 0.05), and six of the seven affected phosphatidylcholines were higher (p < 0.05) in the NH goats compared to the H goats. The results show that habituation reduces fear and stress responses to routine handling, in addition to increasing BW, which can improve the welfare of meat goats.