Antibodies to the zona pellucida in mares

Cross-reactivity tests indicated that the equine zona pellucida shares common antigen(s) with porcine zona. Porcine oocytes were therefore used to test for the presence of zona antibodies in the sera of horses. Serum samples were collected from 65 mares infertile for unexplained causes: 7 mares were strongly positive for antibodies reactive to porcine zona pellucida as determined by an indirect immunofluorescence method. Of these 7 mares, aged 8-23 years, 2 were nulliparous and 5 were multiparous. Zona-covered horse oocytes were treated with sera from 4 mares previously identified as zona positive and 1 zona negative mare. The zona reaction was identical when porcine zona-coated oocytes were treated with the same sera. In a second group of mares, no zona antibodies could be detected in 20 mares greater than or equal to 20 years of age or in 20 mares less than or equal to 10 years of age.