Sperm quality following 4 days of cooled storage: impact on fertility

Abstract

degrade protein components of extracellular matrix and basement membranes, and are thought to be involved in pre-fertilization events. The purpose of this study was to compare the levels of MMP-2 and MMP-9 in different fractions of SP, and to evaluate the correlation of the MMP levels with fertility. During the breeding season, semenwas collected from 43 stallions (20 Standardbreds, 17 Finnhorses, 4 warmblood riding horses, 2 ponies; ages 4-23 years) residing at nine different stud farms in Finland. The breeding history and current use of the stallions was variable, with the stallions serving 2 to 150 (median 14) mares during the season. Semen jets were collected as 1-4 fractions using an open-ended artificial vagina (AV) or a modified closed AV. After semen collection, the gel was removed and the volume of each fraction was measured. A sample representing the whole ejaculate was formed by combining 10% of the volume of each fraction. The samples were centrifuged at 4000 x g (15 min), and the supernatant was filtered using 0.45 mm filters. The SP samples were stored frozen in 1-mL aliquots in -75 C until analyzed. The levels of the pro-form of MMP-2, active MMP-2 and total MMP-9 were evaluated using gelatin zymography and densitometry. Fertility data were provided by the stud farms and the Finnish trotting and breeding association (Suomen Hippos). The first cycle pregnancy rate was calculated from all of the reported matings in the year in question for the stallions included in the study, and all mares that foaled or aborted were considered pregnant. Pro-MMP-2, active MMP-2 and total MMP-9 were detected in stallion seminal plasma, with the highest levels found in the sperm-rich fraction. In all fractions, the levels of proMMP-2 were significantly higher than the levels of active MMP-2 and total MMP-9, which did not differ. The levels of the different types of MMP were not correlated with the first cycle pregnancy rate. Pro-MMP-2, active MMP-2 and MMP-9 are present in all fractions of the stallion's ejaculate, with the highest levels in the sperm-rich fraction. Despite a possible role in the fertilization process, the levels of MMP-2 and MMP-9 were not correlated with fertility in this study on a limited number of animals.