Christi A. Yoder

Field test of a single-injection gonadotrophin-releasing hormone immunocontraceptive vaccine in female white-tailed deer

Thedevelopmentanduseofsafe,effectiveandpracticalwildlifecontraceptiveagentscouldreducereproduction inlocally overabundant deer populationsinsituations where traditionalmanagement toolssuch as regulated huntingcannot be employed. GonaCon Immunocontraceptive Vaccine (the commercial name for a particular gonadotrophin-releasing hormone(GnRH)-basedemulsion)wastestedinadultfemalewhite-taileddeerinafencedherdnearSilverSpring,Maryland, USA. Observations of udder condition were used to identify does that had become pregnant. Necropsy observations, histopathology and serum concentrations of anti-GnRH antibodies, luteinising hormone and progesterone were used to comparehealthandreproductivestatusoftreated(n=28)andcontrol(n=15)deer.AfterreceivingoneinjectionofGonaCon, 88% of treated deer did not become pregnant during the first year and 47% did not become pregnant during the second year aftervaccination.NoadversehealtheffectsrelatedtovaccinationwithGonaConweredetected,exceptforlocalisedinjection- site reactions in five (29%) of 17 examined, vaccinated deer. Treatment with GonaCon can be a safe and effective means of inducingtemporaryinfertilityinwildwhite-taileddeer.Ultimately,themanagementvalueofGonaConwillbedeterminedby natural-resource professionals who use it as one of many tools to manage deer populations.

Effect of GonaCon™ vaccine on black-tailed prairie dogs: Immune response and health effects

Management of prairie dogs in the past has included poisoning, fumigants, barriers, and relocation. Because of the diverse attitudes related to prairie dog management, nonlethal methods that allow the existence of prairie dogs but help minimize damage related to population growth need to be developed. GonaCon™ is an immunocontraceptive vaccine that elicits antibodies to native GnRH; this prevents the secretion of reproductive hormones necessary for sperm and oocyte production. Prairie dogs were vaccinated with 0.1, 0.2, or 0.4 mL of the GonaCon™ emulsion intramuscularly in the upper thigh containing 100, 200, or 400 μg GnRH conjugate, respectively. Control animals were vaccinated with 0.4 mL saline emulsion in the upper thigh. Blood samples (≤1 mL) were taken from the femoral vein once pretreatment and at 1, 2, 3, 4, 6, and 15 months post-vaccination. Age (adult or juvenile) did not affect immune response to GonaCon™. Antibody titers were higher in the 200 and 400 μL GonaCon™ groups than in the 100 μL group, and there was no difference between the 200 and 400 μL GonaCon™ groups. No adverse effects of GonaCon™ were noted on weight or blood chemistry parameters during the study. GonaCon™ will likely contracept prairie dogs for ≥1 year in the field using either 200 or 400 μg conjugate. GonaCon™ could be incorporated into management plans to help maintain prairie dog populations while reducing habitat degradation due to overpopulation.

Diazacon Inhibits Reproduction in Invasive Monk Parakeet Populations

Abstract Throughout the United States, managers lack safe, effective methods to control expanding populations of the invasive monk parakeet (Myiopsitta monachus). Because the reproductive inhibitor diazacon (20,25 diazacholesterol) has been used effectively in captive monk parakeets, we provided diazacon-treated sunflower seeds to birds at electric utility substations inhabited by parakeets in south Florida, USA. Nest productivity (nestlings plus eggs with embryos) averaged 1.31 (SE = 0.45, n = 100 nests) at 6 treated sites compared to 4.15 (SE = 0.68, n = 50 nests) at 4 untreated sites, a 68.4% reduction. Exposure of native bird species to treated bait was infrequent. Diazacon is an effective means to reduce reproductive success of monk parakeets, and development of methods to limit exposure of nontarget birds will enable more widespread use of this useful population management technique.

Effectiveness of several oils to reduce hatchability of chicken eggs

Oiling eggs with white mineral oil was successful with several bird species and has potential as a management tool within an integrated bird management program. We conducted an incubator study from 22 February to 20 March 1995 to determine if castor, corn, linseed, safflower, or soybean oil was as effective as white mineral oil in reducing the hatching success of chicken eggs, and if timing affected treatments (early vs. late incubation). We treated the first sets (9 eggs/set) of eggs on the fifth day of incubation (early) and the second sets of eggs on day 16 of incubation (late). There was a 68% hatching success in control eggs whereas none of the treated eggs hatched. All 5 oils were as effective as white mineral oil in suppressing hatchability of eggs.

Feeding of grey squirrels (Sciurus carolinensis) with the contraceptive agent DiazaCon™: effect on cholesterol, hematology, and blood chemistry

Grey squirrels (Sciurus carolinensis) are an invasive species in Britain and Italy. They have replaced native red squirrels (Sciurus vulgaris) throughout most of Britain, and cause damage to trees. Currently, lethal control is used to manage grey squirrel populations in Britain, but nonlethal methods might be more acceptable to the public. One such method is contraception with 20,25-diazacholesterol dihydrochloride (DiazaCon™). DiazaCon™ inhibits the conversion of desmosterol to cholesterol, resulting in increasing desmosterol concentrations and decreasing cholesterol concentrations. Because cholesterol is needed for the synthesis of steroid reproductive hormones, such as progesterone and testosterone, inhibition of cholesterol synthesis indirectly inhibits reproduction. Desmosterol is used as a marker of efficacy in laboratory studies with species that do not reproduce readily in captivity. Grey squirrels were gavaged with a DiazaCon™ solution for 2 days, and then fed DiazaCon™-coated peanuts for an additional 8 days at target doses of 50 and 100 mg DiazaCon™ per kg body weight. There was a significant difference in cholesterol concentrations in the treatment groups compared to the control group. Cholesterol was reduced by ≥ 40% for 2 months in both treatment groups. There were no differences among groups with respect to blood chemistry and hematology parameters, and mean values are reported. The mean overall dose of DiazaCon™ received was 29.0 ± 1.6 and 55.3 ± 4.3 mg/kg in the low (50 mg/kg) and high dose (100 mg/kg) groups, respectively. DiazaCon™ might provide an effective, acceptable alternative to lethal control.

Use of DiazaCon™ as a reproductive inhibitor for monk parakeets (Myiopsitta monachus)

Feral monk parakeet (Myiopsitta monachus) populations have become established in the United States and other countries around the world, and can cause damage to electrical facilities. Because the monk parakeet is a highly visible species and there is often public opposition to lethal control measures, non-lethal methods, such as contraception, are being developed to help control the spread of feral populations. Two gavage studies and one ad libitum nesting study were conducted to assess the efficacy of DiazaCon™ as a potential contraceptive for the monk parakeet. The first gavage study compared daily dose levels of 0, 50, 75, and 100 mg DiazaCon™ (kg bodyweight) -1 administered for 10 consecu- tive days. Cholesterol concentrations decreased significantly concomitant with a significant increase in desmosterol concentrations in the treated groups, but did not vary between sexes. Cholesterol and desmosterol concentrations did not differ significantly among DiazaCon™ groups, and cholesterol remained significantly suppressed 12 weeks after treat- ment. On the basis of these results, the second gavage study compared 5 or 10 consecutive days of DiazaCon™ adminis- tration at 50 mg kg -1 bird -1 day -1 . Cholesterol concentrations decreased significantly concomitant with a significant increase in desmosterol concentrations in the treated groups, but did not vary between sexes. Cholesterol and desmosterol concentrations did not differ significantly between DiazaCon™ groups, and cholesterol remained significantly suppressed 11 weeks after treatment. Parakeets in the nesting study were fed hulled sunflower seeds treated with a target dose of 50 mg DiazaCon™ kg -1 bird -1 day -1 . Birds consumed enough to receive an average dose of 34 mg kg -1 pair -1 day -1 , or 17 mg kg -1 bird -1 day -1 . Birds in the treated group laid an average of 1.6 ± 0.7 eggs per clutch compared with 3.9 ± 1.1 eggs per clutch in the untreated control group. None of the eggs laid by treated birds hatched compared with 1.1 ± 0.6 eggs per clutch hatching in the control group. Reproductive inhibition was effective for the length of the breeding season, at which time the study was stopped and no more data were collected. DiazaCon™ is a promising avian oral contraceptive that should be further investigated in a field setting with monk parakeets.

Immunocontraception in Eastern Gray Squirrels (Sciurus carolinensis): Morphologic Changes in Reproductive Organs

Abstract: Eastern gray squirrels (EGS) (Sciurus carolinensis) damage trees through bark stripping or gnawing due to territorial marking or agonistic gnawing behavior in concert with higher densities. This study was conducted to determine the effects of a contraceptive vaccine on EGS and its reproductive organ histology. Free-ranging urban EGS were vaccinated with the immunocontraceptive GonaCon™. All EGS were ≥6 mo of age as determined by a combination of pelage characteristics and body weights. The vaccine was administered by injection at a dosage rate of 0.4 ml containing 400 μg of GnRH-mollusk protein conjugate i.m. in the thigh to 33 EGS (17 male [m], 16 female [f]) in trapping session 1 (TS1), 23 (14 m, 9 f) in trapping session 2 (TS2), and 11 (8 m, 3 f) in trapping session 3 (TS3). A sham injection containing 0.4 ml saline-AdjuVac™ was given as control to 22 EGS (16 m, 6 f) in TS1, 20 (12 m, 8 f) in TS2, and 8 (4 m, 4 f) in TS3. In the last trapping session (TS4), 35 EGS (16 treated, 19 control) were killed for necropsy to evaluate histologic changes in testes and ovaries. Treated EGS males had testicular, prostatic, and epididymal atrophy compared with control EGS males. The tubuli seminiferi and prostatic glandular lumen of treated EGS males were atrophic, and the epididymal lumen contained no sperm cells. No histologic changes were observed in treated EGS females; however, females likely were not collected when changes due to GonaCon™ would have been observed. There were no observable histologic differences in the pituitary gland of treated and control EGS. There were no statistically significant differences in either testosterone or progesterone concentrations between control and treated EGS. Although there were no serious side effects to the vaccine, six EGS developed injection site abscesses. GonaCon™ may be a potential tool for EGS population control.

The use of DiazaCon™ to limit fertility by reducing serum cholesterol in female grey squirrels, Sciurus carolinensis

BACKGROUND The grey squirrel, Sciurus carolinensis Gmelin, is an invasive alien species introduced into Great Britain in the late nineteenth century and into Northern Italy during the early twentieth century. Grey squirrels have displaced the native European red squirrel, Sciurus vulgaris L., throughout much of Great Britain and have a significant impact on trees and woodlands through bark-stripping activity. In Britain, eradication is no longer an option at a regional scale, but fertility control offers a non-lethal approach to reducing negative impacts. The cholesterol mimic DiazaCon™ has been successfully used to inhibit reproduction in some species. These studies aimed to evaluate whether DiazaCon™ is effective in inhibiting reproduction in grey squirrels. RESULTS DiazaCon™ reduced serum cholesterol levels in female grey squirrels at a range of doses. The period of effect increased with increasing dose. Reproduction rate was not significantly different between treatment and control groups owing to a lack of breeding in controls. CONCLUSIONS DiazaCon™ has potential to reduce serum cholesterol levels enough and for a sufficient period to reduce fertility in female grey squirrels. Information on baseline physiology and blood chemistry of grey squirrels is required to inform interpretation of the level of significance of the effect.

An evaluation of diazacon as a potential contraceptive in non-native rose-ringed parakeets.

Abstract Rose-ringed parakeets (Psittacula krameri) have become widely established outside their native range through accidental or deliberate release. Potential economic impacts on agriculture, conservation concerns, and mixed public opinion regarding the species have highlighted the need to develop effective but humane management options. Fertility control might provide such a solution if a safe and environmentally benign contraceptive was available. The chemical 20,25-diazacholesterol dihydrochloride (diazacon) has previously been used to reduce reproductive output in avian species through reduction of blood cholesterol and cholesterol-dependent reproductive hormones. We orally dosed captive rose-ringed parakeets with a solution of either 9 mg/kg or 18 mg/kg of diazacon for up to 10 days and found that a dose of 18 mg/kg for 10 days temporarily reduced blood cholesterol levels with no adverse side effects. We evaluated this dose level in a captive population in semi-natural conditions during the 2008 breeding season and found a significant decrease in fertility. We concluded that diazacon has potential for fertility control in this species if a suitable formulation and delivery system is developed for free-living populations.

DiazaCon reduces black-tailed prairie dog reproduction in Colorado

Abstract Context. Black-tailed prairie dogs (Cynomus ludovicianus) often come into conflict with humans in urban natural areas adjacent to private property by destroying plants and denuding the landscape. There is a diversity of attitudes related to urban prairie dog management in Colorado and interest in non-lethal methods is increasing. Therefore, the development of non-lethal methods that allow the existence of prairie dogs and mitigate damage related to population density is needed. Aims. The efficacy of DiazaCon (20,25-diazacholesterol dihydrochloride, a cholesterol analogue) as an oral contraceptive bait for reducing reproduction in black-tailed prairie dogs was tested. Persistence of DiazaCon in black-tailed prairie dogs 11 months after initial application was also determined. Methods. Prairie dogs were baited with DiazaCon-coated rolled oats or control bait for 10 days over a 20-day period in November 2007 on one control and one treatment site. Sites were randomly assigned to a treatment group. Visual counts were used 8 months post-treatment (June/July 2008) to determine pup : adult ratios on both sites. Prairie dogs on both sites were trapped 11 months post-treatment (September/October 2008) to gather mass and age data to assess juvenile : adult ratios and to collect blood samples for determination of serum cholesterol and desmosterol concentrations. Key results. DiazaCon treatment reduced the number of pups per adult by 95.5% when compared with the control site in June/July 2008 (0.09 ± 0.02, n = 10, number of observation days) versus 2.0 ± 0.2 (n = 10). Free serum cholesterol levels in treated animals (370.7 µg mL–1) were lower than control animal levels (411.6 µg mL–1, P < 0.015), while treated desmosterol levels (14.5 µg mL–1) were higher than controls (0.35 µg mL–1, P < 0.02) 11 months after ingestion of DiazaCon bait. However, these differences would likely not have been sufficient to prevent successful breeding in the upcoming breeding season. Conclusions. DiazaCon is an effective contraceptive in black-tailed prairie dogs. It is probably reversible and will likely affect breeding success for only one breeding season. DiazaCon may provide an additional tool to help manage urban populations of prairie dogs in locations where lethal control is unacceptable. Implications. The need for further research into secondary hazards to non-target animals, such as predators, is discussed. Recommendations for field application are also discussed.