Feral horse population growth rates as high as 25% are of concern to those responsible for managing range lands as well as conservation groups. Current methods to control these populations include adoption and long-term holding, which are both costly and controversial. Porcine zona pellucida (pZP) immunocontraception may have the greatest potential to control fertility because it has proven to be effective in other studies and vaccines are easy and safe to administer. One pZP vaccine formulation, SpayVac 1 (ImmunoVaccine Technologies, Inc., Halifax, NS, Canada), has demonstrated single-dose, multi-year contraceptive efficacy in other wildlife species, which would make it both practical and economical for field application. Over a 7-month period during the breeding season, we assessed the effect on ovarian activity of 2 formulations of SpayVac, 1 non-aqueous with modified Freund's adjuvant (MFA) and the other, an aqueous emulsion with MFA, compared to controls (n ¼ 7 per group). Comparative reproductive parameters included serum concentrations of progesterone (P 4 ) determined by enzyme-linked immunosorbent assay (ELISA), ovarian activity assessed by transrectal ultrasound and palpation, as well as gross and histological examination of ovaries upon necropsy (n ¼ 9 or 3 mares from each group) or after ovariectomy (n ¼ 12 or 4 mares from each group). We determined serum antibody titers using ELISA. Mean serum concentrations of P 4 were less in the non-aqueous MFA treatment group compared to control mares (P < 0.025). Ovaries collected from control mares weighed more (P ¼ 0.002) and had greater variation (P ¼ 0.003) than those from either vaccinated group. Both treatment groups also had smaller ovaries and fewer follicles compared to controls (P < 0.001). Three to 4 months after vaccination, 93% of SpayVac-injected mares ceased cycling; whereas all control mares continued to cycle throughout the study. Relatively constant antibody titers were reached by week 6 post-vaccination, although we found appreciable variation within treatment groups, especially 4-8 weeks post-vaccination. Based on our study, the SpayVac formulations impair ovarian function but do not affect other major organ systems, and could provide a safe and effective immunocontraceptive option for mares. Additional research to elucidate the vaccine's mechanism of action, actual contraceptive efficacy, and long-term effects are still needed. Ó 2013 The Wildlife Society.

No abstract

Male Heliothis virescens (F.) were irradiated with 7.5, 15.0, or 22.5 krad of 7-rays and crossed with untreated females. Then fertility of these treated males (PJ and of their descendants was studied for two generations. In addition, the postembryonic survival of the Fx and F2 generations was studied. Fertility (percentage egg hatch) of P1 males was greater than that of Ft males or Fj females. There was more postembryonic survival in the F1 than in the F2 generation. When the Px males received 22.5 krad, few F2 larvae hatched, and none survived. When Pt males received 15.0 krad, the fertility of F1 males and females was less than 5, and 10%, respectively, and less than 20% of the F2 larvae survived; however, sterility factors were nearly eliminated by the third generation. When P1 males received 7.5 or 15.0 krad, the average fertility of F2 males was greater than that of F1 or P1 males but less than that of untreated controls, though fertility of some F2 males was normal. The lower the dose received by P1 males, the greater was the frequency of F2 males with normal fertility.

Sterility induced by gamma irradiation of the adult male tobacco budworm, Heliothis virescens (F.), was studied in two colonies, one was reared in the laboratory for more than 60 generations (laboratory strain) and the other reared for fewer than 9 generations (wild strain). When irradiated males were crossed with untreated females, the percentage egg hatch for each dose was lower with the laboratory than with the wild strain. When laboratory and wild females were crossed reciprocally with irradiated males, the fertilities were similar to those of the laboratory and wild strains, respectively. When irradiated males were crossed with female progeny from reciprocal crosses, the percentage egg hatch was similar to that of the wild strain.Wild strain females were nearly monogamous for the first several generations, but F0 females mated nearly as frequently as females of the laboratory strain.

Can. Ent. 104: 165-172 (1972) Tobacco budworms, Heliothis virescens (F.), with inherited sterility caused by irradiation of the male parent were smaller than progeny from normal parents and developed more slowly throughout the larval and pupal periods. In the second generation the population segregated into two groups, those with normal and those with delayed development. Also, when the PI male received 15.0 krad, 8% of the F, larvae had more than the normal five instars. Moreover, when those F, progeny that had only five larval instars were outcrossed to normal moths, this tendency for supernumerary molts increased nearly 3-fold. The slower development of progeny of treated moths would have to be considered in field tests made to evaluate the effect of inherited sterility on the tobacco budworm. However, with continuous release of irradiated males, the delayed development or smaller size of the progeny should not lessen the possibility that this method could successfully suppress field populations.