Plasma testosterone levels in donkeys in the tropics

Abstract

The concentration of testosterone in the plasma of most male domestic and laboratory animals, for example bulls (Thibier, 1975), boars (Andresen, 1976) and rats (Mock, Kamel, Wright & Frankel, 1975) is usually in excess of 10 nmol/l. In seasonal breeders such as sheep, values as high as 90 nmol/l have been reported in the summer before the breeding season (Falvo, Buhl, Reimers, Foxcroft, Dunn & Dziuk, 1975). In contrast, Katongole (1971) found that in a temperate summer, plasma testosterone concentrations in Equidae, including the donkey, were 4·5 nmol/l or less. It was, therefore, of interest to investigate whether the basal plasma testosterone concentrations in donkeys would be higher and more stable in the tropics.

Six potent adult male donkeys were kept in a large pen, fed rhode grass and given free access to salt and water. Blood