Occurrence of embryo mortality in rabbits isoimmunized against semen.

Abstract

These experiments were undertaken to determine more exactly time and location of mortality in embryos transferred into the reproductive tracts of female rabbits immunized with semen. 14 New Zealand white rabbits were immunized by weekly injections of .5 ml pooled rabbit semen in .5 ml of adjuvant for 3 weeks. After 3-4 weeks a 4th injection was given. The 12 controls were injected with adjuvant or saline or left untreated. 1 or 2 weeks after last immunization all rabbits were injected iv with 75 IU human chorionic gonadotropin (HCg) to induce ovulation. 24-48 hours later 2-to 4-cell embryos were transferred into the oviducts of these rabbits. Embryos were obtained from donors injected daily with .5 mg follicle stimulating hormone in .5 ml beeswax in sesame oil for 3 days prior to HCg injection and either mating or artificial insemination. Recipient rabbits were killed at 2 3 and 4 days after embryo transfer and recovered embryos examined with a phase-interference microscope. The immune rabbits had a decreased perce ntage of normal-appearing and total embryos at 2 and 3 days and by 4 days the decrease was significant 44.8% compared to 63.4% for controls (p less than .05). When 11 rabbits were immunized by 4 weekly injections of .5 ml semen plus .5 mg of Poly A and U followed by booster injections of .75 ml semen and .75 mg each of Poly A and U 2-3 weeks later results were similar. In these experiments both treated and control rabbits were artificially inseminated after HCg-induced ovulation. On the afternoon of Day 4 or the morning of Day 5 the rabbits were killed blastocysts recovered and checked for viability and then transferred to recipient rabbits. The number of implants and viable appearing embryos were determined by Day 9 of pregnancy. Fetal survival rates were determined at autopsy on Day 28 of pregnancy. Antibody titers against seminal antigens were determined. The transferred 4-5 day old blastocysts showed a significant increase in emb ryo mortality before and after implantation in the immune group 41.6% in the immune group compared with 73.2% in controls (p less than .05). Embryo survival between Days 9-28 was 18.7% for immune and 70.2% for control rabbits. (p less than .05). Embryo mortality was not associated with serum titers of antibodies against seminal antigens and spermatozoa.