Jw. Turner et al., REMOTELY DELIVERED IMMUNOCONTRACEPTION IN FREE-ROAMING FERAL BURROS (EQUUS-ASINUS), Journal of Reproduction and Fertility, 107(1), 1996, pp. 31-35
Regulation of local overpopulations of free-roaming feral equids is in
demand worldwide for ecological balance and habitat preservation. Con
traceptive vaccines have proven effective in feral horses, which breed
seasonally, but no data are available for equids such as the burro, w
hich is reproductively active all year round. In the present study, 27
individually identified female feral burros (Equus asinus) roaming fr
ee in Virgin Islands National Park (St John, US Virgin Islands; Lesser
Antilles) were remotely treated with pig zonae pellucidae (PZP) vacci
ne. Between January and May, 16 burros were darted with a 1 mi emulsio
n of PZP plus Freund's adjuvant. Ten to twelve months later each treat
ed burro was given a single booster injection of PZP plus adjuvant to
maintain contraception through a second year. Eleven adult untreated j
ennies served as controls. Beginning one year after initial vaccinatio
n, these burros were monitored for pregnancy and foal production. Coll
ection of data to determine treatment effect was not begun until 12 mo
nths after initial treatment to ensure that pregnancies existing befor
e vaccination were not included. Pregnancy was assessed using previous
ly validated methods for steroid metabolite measurement in fresh faeca
l samples. None of the PZP-treated burros produced foals between 0 and
12 months after the last inoculation. One PZP-treated burro tested po
sitive for pregnancy at 10 months after the final inoculation. During
this same period, six of 11 untreated burros tested pregnancy-positive
, and four were observed with foals. There was no difference in pregna
ncy rates among treated, control and randomly sampled jennies between
12 and 24 months after the last inoculation. The results demonstrate t
hat, in free-roaming feral burros that are reproductively active all y
ear round: (1) burros can be accessed for remotely delivered PZP vacci
nation; (2) PZP contraception is effective; (3) PZP contraception is r
eversible; and (4) pregnancy can be reliably detected by faecal steroi
d analysis.