Sexual behaviour of Zebu bulls in the humid tropics of Costa Rica: single versus multiple-sire groups

This study compares the courtship and mounting behaviour of Bos indicus bulls in single- and multiple-sire groups in Costa Rica (latitude 10 degrees 25'N, longitude 84 degrees 32'W, annual precipitation of 3096mm, temperature of 24 degrees C and humidity of 85.3%). Four, 3-4 year-old Brahman bulls with previous sexual experience were used to sire a group of 120 multiparous cows (average of 128 days post-partum and a body condition score of 2.5) allocated to two groups of 60 each: (1) single-sire mating group (SSM) and (2) multiple-sire mating group of three bulls (MSM). Bulls were rotated among groups every 7 days for 28 days. The frequency, type and duration of sexual activities (mounting and mounting attempts) and courtship activities (smelling and licking genital area, butting, supporting the head over a female and the sign of Flehmen) were calculated for each mating group. Descriptive and non-parametric statistics (Wilcoxon, Mann-Withney tests) were used to calculate differences between mating programmes. Sexual activities tended to be more frequent in the SSM group than the MSM group (267 versus 124, P>0.05). Differences in the ratios of sexual to courtship activities between both groups were significant (1:3 in SSM and 1:6 in MSM, P>0.05). Pregnancy rate averages were 28 and 37%, respectively, (P>0.05). It is concluded that under these conditions multiple-sire mating and single-sire mating achieved similar pregnancy rates.