Relationship between the fertility of fresh and frozen stallion semen and semen quality.

Studies were designed to investigate whether sperm motility determined with a Hamilton-Thorn HTM-2000 motility analyzer (HTM), or the percentage of spermatozoa that passed through glass wool (GW), Sephadex (S), or glass wool/Sephadex (GWS) filters could be used to predict the fertilizing potential of fresh or frozen semen. In the fresh semen study, 10 randomly selected ejaculates from 4 stallions exclusively used for A.I. breeding were assayed during the season. The 521 mares used were inseminated with 500 x 10(6) motile spermatozoa after gynaecological examination every 2 days. In the frozen semen study, 32 ejaculates from 9 stallions were frozen and inseminated into 177 clinically and ultrasonographically normal mares within 12 h of ovulation with 10(9) spermatozoa, regardless of quality. In the fresh semen study, first cycle pregnancies ranged from 25-69% (average 50%) and differed among stallions (P less than 0.05), as did GWS, S, motile spermatozoa (MOT), mean progressive motility (MPV) and lateral head displacement (LHD) (P less than 0.001). GW and GWS filters, but not MOT, ranked the stallions according to fertility. The highest correlations were found between first cycle fertility and GWS (r = 0.86) and between that and MOT (r = 0.80). In the frozen semen study, first cycle and season pregnancy rates among the stallions were 32-70% (average 50%) and 60-90%, respectively. Significant correlations were obtained between the pregnancy rate per cycle and GWS (r = 0.93) and S (r = 0.84), but not between fertility and motility parameters.