Use of heparin to accelerate capacitation of equine spermatozoa in vivo

Abstract

Previous studies have revealed that heparin is capable ics. of accelerating capacitation of equine spermatozoa under in vitro conditions. The objective of this study was to evaluate the ability of heparin to accelerate capacitation of equine spermatozoa in vivo. The experimental protocol involved insemination of mares in the early postovulatory period. Oocyte viability is known to be relatively short following ovulation, thereby leading to lowered pregnancy rates when insemination/breeding is conducted only after detection of ovulation. This experiment was designed to determine whether insemination of mares with spermatozoa pre-incubated in heparin containing extender would enhance pregnancy rates when inseminations were performed following ovulation. To investigate the ability of heparin to accelerate capacitation of stallion spermatozoa in vivo, one stallion and 32 mares were utilized. Mares were inseminated either 0-12 h or 12-24 h after ovulation, with semen diluted in a nonfat milk-glucose extender, with or without added heparin (final concentration of 10 gg/ml). Timing of postovulation insemination tended to affect pregnancy rate (p = 0.07), with an advantage to earlier postovulation breeding. For mares bred within 12 h after ovulation, insemination with gelatinized semen yielded a higher (p = 0.003) pregnancy rate (7 out of 7,. 100%) than did insemination with nonheparinized semen (3 out of 7;43%). For mares bred at 12-24 h after ovulation, a treatment effect was not detected (p = 0. 17). Over all data, insemination with gelatinized semen increased (p = 0.01) the pregnancy rate in mares (12 out of 16,* 75%), as compared to pregnancy rate following insemination with nonheparirlized semen (5 out of 16,. 31%). The effect of heparin on spermatozoa should be tested on additional stallions to determine whether individual stallion variation exists. Nonetheless, these data suggest that heparin accelerates capacitation of spermatozoa under in vivo conditions, thereby enhancing fertilization of locates prior to loss of oocyte viability, when insemination is performed following ovulation.