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Kirkpatrick, J. F., & Turner, J. W. J. (1986). Comparative reproductive biology of North American feral horses. J. Equine Vet. Sci., 6, 224–230.
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Kirkpatrick, J. F., Liu, I. M., Turner, J. W. J., Naugle, R., & Keiper, R. (1992). Long-term effects of porcine zonae pellucidae immunocontraception on ovarian function in feral horses (Equus caballus). J Reprod Fertil, 94(2), 437–444.
Abstract: Ten feral mares free-roaming in Maryland, USA, were inoculated with porcine zonae pellucidae (PZP) protein before the breeding season for three consecutive years (1988-90). Ovarian function was monitored for 51 days during the peak of the breeding season after the third annual PZP inoculation, in seven of these mares and in four untreated control mares, by means of urinary oestrone conjugates and nonspecific progesterone metabolites. None of the ten inoculated mares became pregnant in 1990, compared with 55% of 20 control mares, which included two of the four monitored for ovarian function. Three of the untreated mares demonstrated apparent normal ovarian activity, characterized by preovulatory oestrogen peaks, concurrent progesterone nadirs at ovulation, breeding activity, and luteal-phase progesterone increases after ovulation. Two of the seven monitored PZP-treated mares demonstrated ovulatory cycles that did not result in conception. One was pregnant as a result of conception in 1989 and demonstrated a normal, late-gestation, endocrine profile. The remaining four PZP-treated mares revealed no evidence of ovulation, and urinary oestrogen concentrations were significantly depressed. The experiments indicated that (i) a third consecutive annual PZP booster inoculation is greater than 90% effective in preventing pregnancies in mares and (ii) three consecutive years of PZP treatment may interfere with normal ovarian function as shown by markedly depressed oestrogen secretion.
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Kirkpatrick, J. F., Shldeler, S. E., Lasley, B. L., & Turner, J. W. J. (1991). Pregnancy determination in uncaptured feral horses by means of fecal steroid conjugates. Theriogenology, 35(4), 753–760.
Abstract: This study was carried out to develop an accurate, rapid and inexpensive method for diagnosing pregnancy in uncaptured feral horses by analysis of fecal steroid metabolites and to compare the accuracy of this method with diagnosis by urinary estrone conjugates (E(1)C). Paired urine and fecal samples were collected from 40 sexually mature feral mares during August and October. Urine samples were extracted directly from the soil and analyzed by enzymeimmunoassay (EIA) for E(1)C. Water extracts of fecal samples were assayed by EIA for E(1)C and nonspecific progesterone metabolites (iPdG). Urinary E(1)C, fecal E(1)C and fecal iPdG concentrations for seven mares which produced foals were 3.9 +/- 1.3 (SEM) mug/mg creatinine, 4.2 +/- 0.8 ng/g feces and 1.411 +/- 569.6 ng/g feces, respectively. Urinary E(1)C and fecal E(1)C and iPdG concentrations for the 33 mares which did not produce foals were 0.1 +/- 0.0 mug/mg creatinine and 0.5 +/- 0.1 and 32.8 +/- 4.5 ng/g feces, respectively. These differed (P < 0.01) from values in mares which produced foals.
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Kirkpatrick, J. F., & Turner, A. (2003). Absence of effects from immunocontraception on seasonal birth patterns and foal survival among barrier island wild horses. J Appl Anim Welf Sci, 6(4), 301–308.
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.
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Kirkpatrick, J. F., & Turner, A. (2002). Reversibility of action and safety during pregnancy of immunization against porcine zona pellucida in wild mares (Equus caballus). Reprod Suppl, 60, 197–202.
Abstract: Contraceptive management of publicly valued wildlife species requires safeguards to ensure that these populations are preserved in a healthy state. In addition, reversibility of contraceptive effects and safety in pregnant animals are major concerns. A population of wild horses has been immunized against porcine zona pellucida (PZP) over a 12 year period on Assateague Island National Seashore, MD (ASIS). Mares initially received one or two 65 microg inoculations and once a year 65 microg booster inoculations, all delivered by dart. All young mares aged > 2 years were treated with PZP for 3 consecutive years regardless of whether they have bred successfully and they were then removed from treatment until they had foaled. All mares vaccinated for 1 or 2 consecutive years became fertile again and 69% of mares treated for 3 consecutive years returned to fertility. All five mares treated for 4 or 5 consecutive years have also returned to fertility, but over longer periods of time. Mares treated for 7 consecutive years have not returned to fertility, but several, while still infertile, have started ovulating again. There was no difference in survival rates between foals born to treated and untreated mares, and PZP treatment of pregnant mares did not affect subsequent fertility of their female offspring.
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Kirkpatrick, J. F., & Turner, J. W. (1991). Changes in herd stallions among feral horse bands and the absence of forced copulation and induced abortion. Behav. Ecol. Sociobiol., 29(3), 217–219.
Abstract: Forced copulation and induced abortion were investigated in a herd of feral horses inhabiting a coastal barrier island. Eight mares were diagnosed pregnant in August and October 1989 by means of urinary and fecal steroid metabolites, prior to documented changes in herd stallions. These mares were observed for harassment and forced copulation by the new stallions and for the presence of foals during the spring and summer of 1990. No incidents of harassment or attempts at forced copulation were witnessed and seven of the eight mares produced foals in 1990. These data indicate that forced copulation and induced abortion are not common events among all feral horse herds and suggest reinvestigation of this hypothesized phenomenon.
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Kirkpatrick, J. F., Turner, J. W. J., Liu, I. K., Fayrer-Hosken, R., & Rutberg, A. T. (1997). Case studies in wildlife immunocontraception: wild and feral equids and white-tailed deer. Reprod Fertil Dev, 9(1), 105–110.
Abstract: Non-lethal management methods are required for wild equids that are protected by law and for deer inhabiting areas where lethal controls are not legal or safe. Single or multiple inoculations of porcine zona pellucida (PZP) vaccine have been delivered to wild horses and deer by means of darts. Contraceptive efficacy in horses after two inoculations ranged from 90% to 100%, and after a single inoculation ranged from 19% to 28%. Mares given a controlled-release form of the vaccine had foaling rates ranging from 7% to 20%. No detectable changes in social organization or behaviours among treated horses occurred. Contraceptive effects were reversible after 4 consecutive years of treatment but 5-7 years of treatment resulted in ovulation failure and decreased urinary oestrogen concentrations. Among deer, two inoculations were 70-100% effective in preventing fawns, but one inoculation yielded a contraceptive efficacy of < or = 20%, with pregnancies occurring late in the breeding season; a single annual booster inoculation reduced fertility to 20% in the second year. Energy costs of extended breeding seasons were less than those resulting from pregnancy. After two years of treatment, ovaries appeared normal. These studies suggest that PZP immunocontraception can be successfully applied to certain free-roaming populations of wild horses and deer.
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Kirkpatrick, J. F., Vail, R., Devous, S., Schwend, S., Baker, C. B., & Wiesner, L. (1976). Diurnal variation of plasma testosterone in wild stallions. Biol Reprod, 15(1), 98–101.
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Kirkpatrick, J. F., Wiesner, L., Kenney, R. M., Ganjam, V. K., & Turner, J. W. (1977). Seasonal variation in plasma androgens and testosterone in the North American wild horse. J Endocrinol, 72(2), 237–238.
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Lyda, R. O., Hall, J. R., & Kirkpatrick, J. F. (2005). A comparison of Freund's Complete and Freund's Modified Adjuvants used with a contraceptive vaccine in wild horses (Equus caballus). J Zoo Wildl Med, 36(4), 610–616.
Abstract: Fifteen captive wild mares (Equus caballus) were treated with porcine zona pellucida contraceptive vaccine and either Freund's Complete Adjuvant (n = 7) or Freund's Modified Adjuvant (n = 8). All mares received a booster inoculation of porcine zona pellucida plus Freund's Incomplete Adjuvant a month later. Anti-porcine zona pellucida antibodies were measured over 10 mo following the initial inoculation. There were no significant differences in antibody titers at any point during the 10 mo, and seven of the eight mares in the Freund's Modified Adjuvant group were above the 60% level at the end of the study, which is considered to be the contraceptive threshold for horses. There were no significant differences in titers between pregnant and nonpregnant horses, nor was there a significant correlation between age and titers. One local injection site reaction occurred after booster treatment with Freund's Incomplete Adjuvant, and 11 healthy foals were born during the course of the study. These data suggest that Freund's Modified Adjuvant is an acceptable substitute for Freund's Complete Adjuvant in certain free-ranging and captive wildlife species.
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