Stallion semen has several chemical characteristics not commonly encountered in other animals. It contains very little fructose and the spermatozoa possess only limited fructolytic ability under anaerobic conditions. By determining some of the characteristic constituents such as ergothioneine, citric acid, glycerylphosphorylcholine and certain glycosidases, it is possible to obtain a quantitative measure of the secretory contribution of the ampulla, seminal vesicle and epididymis, respectively, towards the final composition of the whole ejaculate. By analysing separately the various fractions of a split ejaculate, including the so-called tail-end sample, it is possible to detect and pinpoint abnormalities in the functional state of the various male accessory organs and in the entire process of ejaculation.