The HOS test and its relationship to fertility in the stallion

The hypo-osmotic test has been used successfully on equine semen and was co nsidered to be a simple and accessible method which could be a useful addit ion to routine equine semen analysis. It was therefore of interest to deter mine whether the hypo-osmotic test is significantly correlated to Proposed criteria of fertility. The stallions were divided into two groups on the ba sis of threshold levels of fertility. A significant difference (P<0.05) was found between the two groups for the following parameters: progressive mot ility, morphologically normal spermatozoa, percentage of swelling with the hypo-osmotic test, percentage of pregnant mares and number of services per pregnancy. The hypo-osmotic test provided a simple evaluation of membrane f unction and the results obtained show stallions with low swelling scores (< 40%) to be of doubtful fertility. The hypo-osmotic test was not correlated with percentage of pregnant mares but showed a tendency to correlate with t he number of services per pregnancy, therefore it could be an additional me thod for evaluating stallion fertility. Further studies are needed to confi rm this observation.