Reproduction in the zebra stallion (Equus burchelli Antiquorum) from the Kruger National Park

Abstract

Reproductive characteristics of free-ranging zebra stallions are described using data collected from 270 cropped specimens and field observations of live animals. Socially zebra populations comprise coherent family groups dominated by a single stallion and consist of 2-11 individuals including foals. Excess stallions remain solitary or form stallion groups of two to seven individuals. The youngest stallion leading a family group was four years old. On average stallions attain psychological maturity at four and a half years of age, the pubertal interval ranging from age two to four and a half years. The youngest specimen with epididymal spermatozoa was two years old but generally this occurs at three and a half years but behavioural mechanisms prevent mature sub-adult stallions from mating with oestrous mares. Variationin testicle mass and seminiferous tubule diameter indicates that adult stallions have a reproductive peak during the summer (wet season) which coincides with the cycle of the mare. Genital abnormalities included two instances of unilateral testicular hypoplasia and one of bilateral cryptorchidism. Only the latter caused sterility.