Effect of milk fractions on survival of equine spermatozoa.

Milk-based semen diluents are known to be practical and effective in protecting equine spermatozoa during storage. Due to complex composition of milk, the components which are beneficial or harmful to spermatozoa are unknown. To address these unknowns the effect of various milk fractions on motility of stallion spermatozoa was evaluated. The fractions tested were native phosphocaseinate (NPPC), beta-casein, whey protein concentrate (WPC), alpha-lactalbumin, beta-lactoglobulin, microfiltrate, and ultrafiltrate. The standard reference diluents were INRA 82, commercial skim milk, and Hank's salts solution supplemented with Hepes, glucose, lactose (HGLL) supplemented with BSA. After 48 and 96 h storage at 4 or 15 degrees C some milk fractions (ultrafiltrate, microfiltrate, and alpha-lactalbumin fraction) decreased spermatozoal survival. Others (beta-lactoglobulin (BL) and native phosphocaseinate) were protective. Native phosphocaseinate (NPPC) at milk concentration afforted better protection than did the standard reference diluents. The optimal concentration of beta-lactoglobulin afforted significantly better protection than did BSA. The protection afforded by native phophocaseinate was not synergistic with beta-lactoglobulin. This implies a similar mechanism of protective action of these two components. Semen diluted in HGLL supplemented with NPPC (HGLL-NPPC) or in INRA 82 and stored 24 h at 15 degrees C or 4 degrees C, respectively, produced no difference of spermatozoal motility. However, fertility of semen stored in HGLL-NPPC (60%) was higher (p < 0.05) than that stored in INRA 82 (36%).