The ‘tail-end sample’ of stallion semen

Abstract

1. Measurements of volume, sperm density, ergothioneine, sulphydryl groups and citric acid were made in 100 ‘tail-end samples’ (post-coital penis drips) from thirteen thoroughbred stallions. In addition, a few analyses were made of postcoital vaginal samples.2. The ‘tail-end samples’ were found to differ substantially in their composition from that of the whole ejaculates. They lacked the characteristic gelatinous appearance of normal stallion semen, and had a much lower content of spermatozoa, ergothioneine (sulphydryl groups) and citric acid than an average stallion ejaculate.3. As the variations in volume and composition of the ‘tail-end samples’ collected from different stallions or from the same stallion on different occasions were considerable, it is unlikely that prognostication of fertility could be usefully based on results obtained by analysis of such samples.