Bull-switching in African Bovid Herds: Assessing Best Practices for Breeding Management in Waterbuck

Abstract

To implement sustainable ex-situ management of big ungulate herds such as African Waterbuck (Kobus ellipsiprymnus), one strategy is to place a vasectomized male with females during the sub-optimal season for breeding and subsequently replace him with an intact male during the optimal breeding season. However, information is needed on the effects of vasectomy and the long-term effects on social well-being of individuals used in this "bull-switching" treatment, which is designed to enhance well-being of the whole herd. In this study, behavioral observations were conducted in three periods (pre-treatment, treatment, post-treatment) 2-months in length. Focal individual observations were used to systematically record (a) continuous samples on video (6-min duration; n = 595), (b) instantaneous samples of proximity (n = 951), and (c) field notes of all-occurrences of social interaction (courting and antagonistic). The quantitative and qualitative analyses revealed a significant effect of treatment on three (courtship, escalation, and proximity) out of four measures (deescalation was not affected). Courtship and escalation behaviors increased significantly during the treatment (G2 = 46.35; df=1, P <0.001; z=6.60). The treatment was associated with a significant change in proximity for females (G2 = 17.21; df=1; P <0.001; z=2.31) and other males (G2 =16.10; df=1; P <0.001; z=-3.57). Overall, (1) there was no substantial change with social well-being of the vasectomized male before removal and after reintroduction; (2) the male proximity did not fluctuate significantly with the juvenile males, calves, and other species; and (3) the vasectomized male and the intact male exhibited similar social well-being characteristics. Considering current environmental changes, the treatment did not result in a decline of the social well-being of females and calves, but it did for non-breeding males. Courtship declined in post-treatment, but this was due to the increased percent of pregnant females. During post-treatment, a change in ratio of green grass and supplementary feed pellets possibly affected de-escalation in the context of interspecies interactions. The change of the proximity of the herd was associated with increased heat and use of shaded areas in the pasture. The treatment resulted in a change in relationship with the satellite male and juvenile males in the herd.