| The effects of semen extender components on the ability of stallion sperm to bind to the zona pellucida (ZP) and, the suitability of using bovine ZP for a ZP-binding assay for stallion sperm were investigated in a series of experiments. Similar numbers of stallion sperm bound to bovine and equine ZP, demonstrating suitability of bovine ZP for a binding assay with stallion sperm. Presence of milk and milk proteins, particularly native phosphocaseinate (NP) and sodium caseinate (SC), during sperm-ZP interactions resulted in a three- to seven-fold increase in number of sperm bound to ZP.; In the second series of experiments, the effects of caseins (alpha-, beta- and kappa-caseins) on binding of stallion sperm to ZP were investigated. In addition, the effects of extracellular Ca2+ and milk proteins on intracellular Ca2+ concentration in sperm were investigated. Results demonstrated that increased extracellular Ca2+ concentration in the medium did not affect baseline intracellular Ca2+ concentration in the sperm. Milk proteins (NP and SC) did not affect the uptake of Ca 2+ by sperm.; In conclusion, milk proteins significantly enhanced sperm binding to ZP. The beneficial effect of NP and SC on sperm binding to ZP does not appear to involve increasing intracellular Ca2+. Further studies are necessary to determine the mechanism(s) by which milk proteins enhance sperm binding. Findings from these studies can be used to increase our understanding about sperm and ZP interactions in the horse. In addition, the suitability of bovine oocytes for studies on gamete interaction may be beneficial to further the development of IVF in the horse. |
