Fertilization and early embryonic development in androstenedione-immunized Merino ewes

Abstract

Ewes were immunized against androstenedione (Fecundin) and assigned to be mated 14 days (179 ewes Group C) or 25 days (174 ewes Group B) after a booster immunization with Fecundin. The anti-androstenedione titres at these times were 6790 and 3240 respectively (P less than 0.01). The remaining 169 ewes were untreated controls (Group A). Ewes were mated to entire rams (12 rams to 180 ewes) at their second oestrus after synchronization of oestrus. Immunization against androstenedione caused a shortening of the time from sponge removal to mating (Day 0) and a decrease in the percentage of ewes mated by the rams. Also, ovulation rate was increased after immunization (P less than 0.01), being 1.42, 2.16 and 1.93 for Groups A, C and B respectively. Egg recovery rates on Day 2 were lower in immunized ewes and there was some indication that fertilization rates were lowered. On Day 13 after mating a higher proportion of blastocysts was recovered from ewes in Group A than from those in Groups B and C. Immunization resulted in lower fertilization rates and smaller blastocysts with lower mitotic indexes (P less than 0.01). At Days 24-32 of pregnancy fetal weight was lower in the immunized ewes. At all sampling stages, the proportion of ewes pregnant (fertility) was lowered in immunized ewes. The results of the present study show that significant reproductive wastage occurs in androstenedione-immunized Merino ewes, with lower rates of embryo recovery and delayed embryonic development being found in comparison to controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive wastage in the androstenedione-immune ewe

“…The results presented in this paper confirm and extend our earlier findings (Boland et al, 1986) that Merino ewes immunized against androstenedione suffer from increased levels of early embryonic wastage if they are mated too soon after receiving their repeat (booster) immunization. The optimum time for mating is from 21 to 35 days after a repeat immuniza¬ tion (Geldard et al, 1984) and in this experiment a mating system was selected, with a 13-14 day interval, that would produce a high level of embryonic death and facilitate our objectives.…”

“…Intravaginal sponges (Repromap: Upjohn Pty Ltd, Rydalmere, NSW) were inserted for 12 days and removed 5 days before the booster immunization. Fertile mating at the second oestrus, after removal of the progestagen pessaries, was timed to occur about 14 days after booster immunization, a time equivalent to that which produced the highest level of reproductive wastage in our earlier experiments (Boland et al, 1986). After removal of the pessaries, 15 (10%) vasectomized Merino rams fitted with mating harnesses and coloured raddles (Sire-Sine: Hortico Australia Pty Ltd, NSW) were introduced to the flock which was then examined every 4 h for the presence of ewes in oestrus.…”

“…Antibody titres were also measured in 30 samples of uterine flushings collected on day 9 or days 13-14 of pregnancy. Antibody titres were deter¬ mined by a radioligand binding method (Boland et al, 1986) and are reported as the dilution of serum that binds 50% of added ligand.…”

“…The gain in lambing percentage is usually less than the corres¬ ponding gain in ovulation rate; this difference is almost entirely due to post-ovulatory reproductive wastage. In an earlier study we attempted to partition these reproductive losses in control and androstenedione-immune ewes by estimating reproductive performance at three times after mating (Boland et al, 1986). Two major sources of reproductive wastage were identified: the Present addresses: "Department of Animal Science, University of California Davis, Davis, CA 95616, USA; fDepartment of Geriatrics, Concord Repatriation Hospital, PO Box 152 Concord 2137, NSW, Australia.…”

“…first appeared within three days of the onset of oestrus and the second appeared later, but before day 13. The first source of reproductive wastage, only present in androstenedione-immune ewes, was detected as a reduction in embryo recovery rate at day 2 after mating (Boland et al, 1986). The second major source of waste, which occurred in both untreated and immunized ewes, was detected as a reduced percentage of normal, expanded blastocysts recovered on day 13 of preg¬ nancy.…”