CHANGES IN THE BEHAVIOR AND ANDROGEN LEVELS DURING PUBERTAL DEVELOPMENT OF THE BUFFALO BULL

Sexual behaviour and peripheral testosterone concentrations were studied longitudinally in a group of ten buffalo bulls of Nili-Ravi breed raised from birth under similar feeding and management conditions. Changes in sexual behaviour of these animals in response to a teaser bull were observed at weekly intervals from 15 months of age to attainment of puberty (mean age at puberty, 23.6 +/- 0.9 months). Sexual behaviour of individual bulls was scored by a procedure based on an assessment of behavioural events and expressed as a percentage of the maximal points. These events ranged from reaction of the bull during approach towards the teaser to intromission and ejaculation in an artificial vagina. Serum testosterone was determined by radioimmunoassay in blood samples obtained at monthly intervals, from each bull. Analysis of behavioural data indicated a significant increase in sexual behaviour score (from 5 +/- 2% to 40 +/- 7%) 4-5 months prior to the attainment of puberty. Following a transitory decline, the sexual behaviour score reached a maximum (69 +/- 5%) during the month in which first ejaculation with motile sperm was achieved. Behavioural profiles of individual bulls indicate that the period of prepubertal increase in sexual activity corresponded to the physiological puberty rather than to the chronological age of the bulls. The prepubertal as well as pubertal increase in sexual behaviour score was invariably preceded by a significant (P < 0.05) elevation of serum testosterone concentrations. The data suggests that the prepubertal increase in sexual activity in the buffalo bull may serve as a criterion of onset of puberty and may be helpful in the selection of sires at a stage prior to sexual maturation.