Absence of Effects From Immunocontraception on Seasonal Birth Patterns and Foal Survival Among Barrier Island Wild Horses

Abstract

Despite a large body of safety data, concern exists that porcine zonae pellucidae (PZP) immunocontraception--used to manage wild horse populations--may cause out-of-season births with resulting foal mortality. Our study at Assateague, Maryland indicated the effects of immunocontraception on season of birth and foal survival between 1990 and 2002 on wild horses from Assateague Island. Among 91 mares never treated, 69 (75.8%) of foals were born in April, May, and June (in season). Among 77 treated mares, 50 (64.9%) were born in season. Of 29 mares foaling within 1 year after treatment (contraceptive failures), 20 (68.9%) were born in season. Of 48 mares treated for greater than 2 years then withdrawn from treatment, 30 (62.5%) of 48 foals were born in season. There were no significant differences (p <.05) between either treatment group or untreated mares. Survival did not differ significantly among foals born in or out of season or among foals born to treated or untreated mares. Data indicate a lack of effect of PZP contraception on season of birth or foal survival on barrier island habitats.

Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations

“…July, a majority of the foals were born in the spring months of April and May to both treated and control females and this is consistent with other feral horse populations (Kirkpatrick and Turner 2003). These data suggest that contraceptive treatment does not significantly impact the timing of foal births or foal survival in feral horses.…”

“…A chi-squared test was used to test for differences between foal sex ratios, seasonality of births and foal survival. We defined the foaling season to include April, May and June (Kirkpatrick and Turner 2003). Results are shown as means ± standard errors where appropriate.…”

“…For example, several studies have shown the contraceptives alter breeding behaviour of females which results in a lengthened breeding season and later offspring birth dates (McShea et al 1997;Heilmann et al 1998;Miller et al 2000b). However, a study on PZP showed no difference in the month that foals were born to females where contraception was waning (Kirkpatrick and Turner 2003). Several studies have also reported increased body condition of treated females in wild species (McShea et al 1997, Turner and.…”

Milestones in contraceptive vaccines development and hurdles in their application

“…Long-term follow-up of the porcine ZP immunized wild horses and white-tailed deer did not reveal any significant debilitating health effects. [105][106][107] The potential of porcine ZP-based contraceptive vaccine to control the population of African elephant (Loxodonta africana) has also been explored ( Table 1). 108 …”

“…Longterm follow-up studies of the porcine ZP-based contraceptive vaccine immunized feral horses and white-tailed deer revealed no significant deleterious effects on the health of the immunized animals except oophoritis. [105][106][107] Follow-up of the immunized feral horses between 1990 to 2002 revealed no significant effect of porcine ZP contraception on the season of birth or foal survival as compared with unvaccinated feral horses habitating Assateague Island National Seashore, Maryland, USA. 106 The block in fertility was reversible.…”