Effects of the peri-pubertal rearing environment on endocrine and behavioural responses to oestrous female exposure in the mature bull

Abstract

The objective of this study was to determine the impact of the peri-pubertal rearing environment upon subsequent endocrine and behavioural responses of the bulls to oestrous female exposure. Thirty Angus bulls were allotted to one of three rearing environments at 10–11 months of age: on pasture (male contact only, CON); on pasture with male contact and female contact for 2 h at 28-day intervals (female-exposed treatment, EXP); or penned individually which restricted direct physical contact with other animals (IND). Environmental conditions were maintained for 8 months after which bulls were observed during a single 30-min exposure to an oestrous female with concurrent blood sampling. Significantly elevated serum cortisol concentrations were a result of the female contact period in CON, EXP and IND bulls. Detectable increases in growth hormone were evident during oestrous female exposure in IND bulls ( P<0.01). This observation was absent in CON and EXP bulls. Increased mean testosterone levels were measured subsequent to the period of female exposure in all bulls. Of the behavioural events recorded, only the elapsed time to first mounting was different between environmental rearing groups. The CON bulls were slower to initiate mounting than EXP and IND bulls ( P<0.07). These results suggest that the rearing environment, at or near the time of puberty, can alter subsequent endocrine responses during mating with little or no effect on behavioural parameters during the post-pubertal period of the bull.