Hypo-Osmotic Swelling Test (HOST) for Feline Spermatozoa: The Simplified Procedure and the Aspect of Sperm Morphology

SIMPLE SUMMARY: One of the methods used to assess semen quality is the hypo-osmotic swelling test (HOST). Different protocols for this test are available, including a very simple one: swelling of spermatozoa is induced by incubation in distilled water for 5 min. Such a protocol could have easily been introduced in clinical practice, but it has not yet been evaluated for feline sperm cells. The objectives of this study were: (1) to check if a simplified HOST procedure can be applied for feline semen and (2) to check if sperm abnormalities may influence the results of this test. The results proved that the simplified HOST gives the same results as the standard one and that the presence of live, abnormal spermatozoa does not interfere with the test results. ABSTRACT: Hypo-osmotic swelling test (HOST) is used to assess the functional integrity of sperm plasma membranes in many species. The primary aim of this study was to test a simplified HOST procedure for the evaluation of feline semen. The second objective was to check if sperm abnormalities can influence the results of this test. Urethral semen was collected from 19 male, domestic cats. In Exp. 1, HOST was performed in different media (50 mOsm/kg fructose or distilled water), temperature (37 °C or room temperature) and time (5 and 30 min). In Exp. 2, the potential effect of sperm abnormalities on HOST results was assessed by observing individual normal and abnormal spermatozoa microinjected into droplets of distilled water. The results showed no differences between the HOST results performed in different media, temperature and time. Viable abnormal spermatozoa were able to swell under hypo-osmotic conditions in the same manner as normal ones, except spermatozoa with distal droplets, which showed a higher frequency of ‘despiralization’. In conclusion, HOST can be reliably performed at 0 mOsm/kg for 5 min at room temperature, which may contribute to a wider use of this test under clinical environments. Viable abnormal spermatozoa are able to swell under hypo-osmotic conditions; therefore, their presence in the ejaculate would not bias the results of HOST when total coiling is calculated.