| Abstrakt: |
A seven-year study was conducted to determine the effects of long-term treatment of wild mares with a porcine zona pellucida (PZP) immunocontraceptive vaccine on fertility, urinary estrogen and progesterone metabolite concentrations, ovulation rates, and reversibility of contraceptive effects. Fifty free-roaming mares were inoculated remotely with PZP in March over 7 consecutive years (1988–1994). During the initial year of treatment, each mare received either one (n = 14), two (n = 18), or three (n = 18) inoculations (2-3 wk apart) of 65 μg of native PZP; each received a single annual booster inoculation thereafter. Alternate-day urine samples were collected directly from the sand after witnessed eliminations. Collections covered 60 days during the peak of the breeding season. Ovarian endocrine function was monitored by means of urinary estrone conjugates (E1C) and nonspecific progesterone metabolites (iPdG). PZP treatment over 6 yr, equaling 105 mare-years, resulted in four foals (3.8%) compared to a 46.2% foaling rate for the untreated population. Twenty-seven mares received their initial inoculations during the later stages of pregnancies (280–340 days), and all 27 delivered foals. Twenty-one of these foals lived to 1 yr, and this survival rate (77.7%) did not differ significantly from that of 25 foals (84% survival rate) born to untreated mares. As evidenced by pregnancies or luteal phase iPdG patterns and concentrations, ovulation rates declined over 6 consecutive years of treatment. The ovulation rates after a single year of treatment, 3 consecutive years, and 7 consecutive years were 73.3% (11 of 15), 55.5% (5 of 9), and 10% (1 of 10), respectively. One mare was withdrawn from treatment after 5 consecutive years of treatment and ovulated during the sixth and seventh years of the study.After a single year of treatment, 12 of 15 mares (80%) had urinary E1C concentrations that fell within the normal range of 100-385 ng/mg creatinine (Cr). After 2, 3, 6, and 7 yr of consecutive treatment, the percentage of mares with normal urinary estrogen concentrations declined to 46.1% (6 of 13), 33% (2 of 6), 40% (2 of 5), and 0% (0 of 5), respectively. Some mares with decreased urinary E1C concentrations continued to demonstrate cyclic peaks and nadirs, suggesting continued but diminished follicular activity. Reproductive behaviors were correlated with elevated urinary E1C concentrations. Reversibility of contraceptive effects after 1, 2, 3, and 4 consecutive years of treatment was 70% (7 of 10), 66% (2 of 3), 10% (1 of 10), and 50% (1 of 2), respectively. The results of this study indicate that long-term PZP treatment leads to a decline in both ovarian estrogen production and ovulation rates, and that reversibility of effects occurs in some animals. |
