Immunocontraception and increased longevity in equids

Intensive population management by means of fertility control has been shown to change the age profile of a wild horse herd. The primary change has been an increase in the number and percent of older animals, as expected, but also the appearance of new and older age classes. An examination of direct effects of fertility control on two groups of treated animals shows a significant increase in longevity over non‐treated animals that is associated with contraceptive treatment. The mean age at death (MAD) was calculated for 128 wild horses for which precise birth and death dates were known, including 56 stallions, 42 untreated mares, 11 mares treated with a porcine zona pellucida contraceptive vaccine for 1–2 years, and 19 mares treated with the same vaccine for ≥3 years. The MAD for stallions (10.3±0.84 [SEM] years), and mares treated for 1–2 years (10.2±0.56), was significantly greater (P<0.05) than for untreated mares (6.4±0.85), and significantly <19.9±1.66 for mares treated ≥3 years (19.9±1.66). Zoo Biol 26:237–244, 2007. © 2006 Wiley‐Liss, Inc.     

A Sightability Model for Mountain Goats

ABSTRACT Unbiased estimates of mountain goat (Oreamnos americanus) populations are key to meeting diverse harvest management and conservation objectives. We developed logistic regression models of factors influencing sightability of mountain goat groups during helicopter surveys throughout the Cascades and Olympic Ranges in western Washington during summers, 2004–2007. We conducted 205 trials of the ability of aerial survey crews to detect groups of mountain goats whose presence was known based on simultaneous direct observation from the ground (n = 84), Global Positioning System (GPS) telemetry (n = 115), or both (n = 6). Aerial survey crews detected 77% and 79% of all groups known to be present based on ground observers and GPS collars, respectively. The best models indicated that sightability of mountain goat groups was a function of the number of mountain goats in a group, presence of terrain obstruction, and extent of overstory vegetation. Aerial counts of mountain goats within groups did not differ greatly from known group sizes, indicating that under-counting bias within detected groups of mountain goats was small. We applied Horvitz-Thompson-like sightability adjustments to 1,139 groups of mountain goats observed in the Cascade and Olympic ranges, Washington, USA, from 2004 to 2007. Estimated mean sightability of individual animals was 85% but ranged 0.75–0.91 in areas with low and high sightability, respectively. Simulations of mountain goat surveys indicated that precision of population estimates adjusted for sightability biases increased with population size and number of replicate surveys, providing general guidance for the design of future surveys. Because survey conditions, group sizes, and habitat occupied by goats vary among surveys, we recommend using sightability correction methods to decrease bias in population estimates from aerial surveys of mountain goats.     

Microsatellite analysis revealed genetic diversity and population structure among Chinese cashmere goats

Most cashmere goats are found in northern China and Mongolia. They are regarded as precious resources for their production of high quality natural fibre for the textile industry. It was the first time that the genetic diversity and population structure of nine Chinese cashmere populations has been assessed using 14 ISAG/FAO microsatellite markers. In addition, two Iranian populations and one West African goat population were genotyped for comparison. Results indicated that the genetic diversity of Chinese cashmere goats was rich, but less than those of the Iranian goat populations. All pairwise F_ST values between the Chinese cashmere goat populations reached a highly significant level (P < 0.001), suggesting that they should all be considered as separate breeds. Finally, clustering analysis divided Chinese cashmere goats into at least two clusters, with the Tibetan Hegu goats alone in one cluster. An extensive admixture was detected among the Chinese goat breeds (except the Hegu), which have important implications for breeding management.     

Population Response of Giant Galápagos Tortoises to Feral Goat Removal

Efforts to eradicate nonnative mammals to restore oceanic island ecosystems have become increasingly successful but parallel tracking of response by native species for which control efforts are intended to benefit has been rare. A major campaign to eradicate nonnative goats and burros was initiated in 1995 on Alcedo Volcano in the Galápagos Archipelago that ultimately removed 62,868 goats and eliminated them by 2006. Planners of the eradication program had the foresight to invest in intensive monitoring of the status of the volcano's giant tortoise (Chelonoidis nigra) population whose welfare was a primary motivation for the eradication effort. Monitoring revealed an increase in the proportion of juveniles among all tortoises as well as increased growth rates of individual tortoises on Alcedo Volcano from earlier to later phases of the eradication campaign. Over the same time frame in a control population on nearby Santa Cruz Island (where goats and donkeys were not removed) juvenile fraction and individual growth rates remained unchanged. Although goat removal coincided with occurrence of a rare climatic event that simultaneously boosted forage availability for tortoises, failure to observe a comparable improvement in the control population implies that removal of goats and burros was the primary causative factor of improving population status of tortoises on Alcedo Volcano.     

Fraternal polyandry and fertility in a high Himalayan valley in Northwest Nepal

The manner in which cultural factors affect fertility has become an important area of anthropological concern. In this article, it will be shown that while fraternal polyandry does not affect individual fertility it does have a significant depressing effect on aggregate fertility and functions, unperceived and unintended, as an important mechanism for reducing population growth.This work was supported by a fellowship from the American Council of Learned Societies.     

Estimating Abundance and Simulating Fertility Control in a Feral Burro Population

Overabundant populations of feral equids are negatively affecting rangelands in the western United States. To better manage these populations, robust estimates of abundance and demographic rates and cost-effective methods of reducing abundance are necessary. From August 2015 to April 2017, we estimated the abundance of feral burros (Equus asinus) at the Fort Irwin National Training Center (NTC; California, USA) using a double-observer-sightability aerial survey method; captured, radio-collared, and inoculated female burros with porcine zona pellucida (PZP), an immunocontraceptive control agent; estimated female demographic rates; and used matrix population models to simulate how changes in demographic and PZP delivery rates would influence burro abundance. We estimated there were 690 (95% CI = 618–752) feral burros within the surveyed area, but these are part of a much larger population that is not geographically isolated from those in the survey area. Sighting probabilities ranged from 0.19–0.98 and were most strongly influenced by distance from observer and group size. We estimated age-specific demographic rates at the NTC and compiled mean rates across burro populations in arid environments from the literature. Mean fecundity varied from 0.17 to 0.58 foals/adult female with younger females having lower fecundity. Mean survival was 0.90 for foals, 0.98 for yearlings, and 0.96 for adults. The PZP vaccine treatment strategies that suppressed fertility for up to 10 years predicted that burro abundance would be reduced by 67–88% after 15 years (compared with no treatment), but none of these strategies resulted in population extirpation. Population growth rates shifted from increasing to decreasing at adult survival rates below 0.84 and the population was predicted to become extirpated when adult survival declined to <0.60. In the absence of other methods to reduce burro numbers, our findings indicate that current formulations of PZP immunocontraception, which require multiple doses, would be inadequate for controlling population growth rates at the NTC. Our fieldwork also highlighted the difficulty of administering PZP vaccination to large, free-ranging animals. Development of longer-term fertility reduction agents or more efficient vaccine delivery techniques would likely improve the efficacy of fertility control for overabundant ungulate populations. Lack of geographic closure (physical barriers to migration) further complicated efforts to reduce burro numbers. © 2021 The Wildlife Society.     

Long-term fertility control in female cats with GonaCon™, a GnRH immunocontraceptive

The uncontrolled reproduction of free-roaming feral cats contributes to overpopulation and associated concerns regarding their welfare and impact on public health and the environment. Nonsurgical fertility control that could be administered to feral cats in the field would be a powerful tool for cat population control. The objective was to test the efficacy and duration of activity of a single-dose GnRH immunocontraceptive vaccine (GonaCon?) on the fertility of adult female laboratory cats. Vaccinated cats (n = 15) received a single injection of vaccine containing a GnRH-KLH conjugate (200 μg) emulsified in a mycobacterial and oil adjuvant on study Day 0. Sham-treated cats (n = 5) received a single injection containing all vaccine components except the GnRH-KLH conjugate. A breeding trial started on study Day 120. Vaccinated cats had a longer time to conception (median 39.7 mo) compared to sham-treated cats (4.4 mo; P < 0.001). A total of 93% of vaccinated cats remained infertile for the first year following vaccination, whereas 73, 53, and 40% were infertile for 2, 3, and 4 y, respectively. At study termination (5 y after a single GnRH vaccine was administered), four cats (27%) remained infertile. The GnRH antibody titers declined more rapidly in short-term responding cats with < 2 y of infertility (n = 4), compared to long-term responding cats that experienced fertility control for >2 y (n = 11) (P < 0.05). Non-painful but persistent late-onset granulomatous injection site masses appeared 2 y after initial vaccination in five cats. We concluded that GnRH immunocontraception is an ideal candidate for further development for feral cat control.     

Extinction threats of a narrowly endemic shrub, Stachyurus macrocarpus (Stachyuraceae) in the Ogasawara Islands

Stachyurus macrocarpus is a narrowly endemic endangered shrub of which only one population remains on Chichi-jima Island (Ogasawara). We surveyed its population dynamics and reproductive states for 4 years and analyzed the population viability. In a survey of its entire distribution range, a total of 87 S. macrocarpus individuals have been found and 68 individuals have been confirmed in 2007. Thus, the actual population size is estimated to be less than 100 individuals. Environmental conditions and the results of a hand-pollination experiment suggest that low fruit setting in both sexes (female: 4.9–11.2%; hermaphrodite: 0.0%) may be caused by resource limitation. In addition, fruit predation by alien Rattus rattus was observed despite the rare fruit setting. The small effective population size (23.1–24.6 individuals) and hermaphrodite-biased sex ratio (46 hermaphrodites:12 females) would increase the risk of extinction. The habitat of S. macrocarpus was limited to dense scrubland and forest understory, and seedling regeneration was very scarce. During the survey period, 19 individuals (21.8%) were found dead, there were only two seedling recruitments, and the annual population growth rate was 0.979. The lack of occurrence on the south and west slopes and the shortness of shrubs in open spaces suggests that S. macrocarpus suffers stress from both dryness and frequent typhoons. However, S. macrocarpus also exhibited high mortality of shoot in forest understories. These findings suggest that the suitable habitat of S. macrocarpus is likely to be narrow in Ogasawara. While the recent increase of goat grazing has not affected individual mortality, 58.6% of shoots that had been grazed by goats were dead within 2 years. As elasticity analysis had shown that larger individuals make a greater contribution to the population growth rate, repeated goat grazing would impact the S. macrocarpus population in the near future by decreasing the vitality of larger individuals. Emergency measures for protecting the shrub from goat grazing and reinforcing the population through nursery cultivation were proposed.     

The effects of spirotetramat on life history traits and population growth of Tetranychus urticae (Acari: Tetranychidae)

The effects of spirotetramat, a tetramic acid derivative, on gross fertility, net fertility, female longevity and the instantaneous rate of increase of two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) were investigated after treatment of female teleiochrysalises (the first assay) and pre-ovipositional females (the second assay). Spirotetramat was applied to the leaf discs by Potter spray tower and the following series of concentrations was applied: 200, 60, 18, 5.4 and 1.62 mg/l. In both assays after 24 h of exposure, surviving females without symptoms of poisoning were used for further procedure. In the first assay, gross fertility of treated females was reduced by 2.4–64.7% and net fertility by 12.4–88.8%, compared to the control. Gross fertility of the females treated with 1.62 and 5.4 mg/l did not significantly differ from the control, whereas all concentrations, except the lowest, significantly reduced net fertility and female longevity. Treatments with 200, 60, and 18 mg/l significantly reduced the instantaneous rate of increase. In the second assay, gross fertility and net fertility were reduced by 43.7–93.3% and 73.8–98.5%, respectively. All concentrations, except the lowest, significantly reduced gross fertility, whereas net fertility and longevity in all treated females were significantly lower compared to the control. All concentrations, except the lowest, significantly reduced the instantaneous rate of increase, provided that concentrations of 200, 60 and 18 mg/l caused population decline. The effects of spirotetramat and its impact on T. urticae management are discussed.     

Nonsurgical fertility control for managing free-roaming dog populations: A review of products and criteria for field applications

About 75% of dogs worldwide are free to roam and reproduce, thus creating locally overabundant populations. Problems caused by roaming dogs include diseases transmitted to livestock and humans, predation on livestock, attacks on humans, road traffic accidents, and nuisance behavior. Nonsurgical fertility control is increasingly advocated as more cost-effective than surgical sterilization to manage dog populations and their impact. The aims of this review were to 1) analyze trends in numbers of scientific publications on nonsurgical fertility control for dogs; 2) illustrate the spectrum of fertility inhibitors available for dogs; 3) examine how differences between confined and free-roaming dogs might affect the choice of fertility inhibitors to be used in dog population management; and 4) provide a framework of criteria to guide decisions regarding the use of nonsurgical fertility control for dog population management. The results showed that the 117 articles published between 1982 and 2011 focussed on long-term hormonal contraceptives, such as gonadotropin-releasing hormone agonists, immunocontraceptives, and male chemical sterilants. The number of articles published biennially increased from one to five papers produced in the early 1980s to 10 to 20 in the past decade. Differences between confined dogs and free-roaming dogs include reproduction and survival as well as social expectations regarding the duration of infertility, the costs of sterilization, and the responsibilities for meeting these costs. These differences are likely to dictate which fertility inhibitors will be used for confined or free-roaming dogs. The criteria regarding the use of fertility control for dog population management, presented as a decision tree, covered social acceptance, animal welfare, effectiveness, legal compliance, feasibility, and sustainability. The review concluded that the main challenges for the future are evaluating the feasibility, effectiveness, sustainability, and effects of mass nonsurgical sterilization campaigns on dog population size and impact as well as integrating nonsurgical fertility control with disease vaccination and public education programs.     

Sperm specific proteins-potential candidate molecules for fertility control

The increase in population growth rate warrants the development of additional contraceptive methods that are widely acceptable, free from side effects and less expensive. Immunocontraception, and in particular the targeting of antibodies to gamete-specific antigens implicated in sperm egg binding and fertilization, offers an attractive approach to control fertility. The development of a contraceptive vaccine based on sperm antigen represents a promising approach to contraception. In mammals, fertilization is completed by the direct interaction of sperm and egg, a process mediated primarily by sperm surface proteins. Sperm have proteins that are unique, cell specific, immunogenic and accessible to antibodies. A few of the sperm specific proteins have been isolated and characterized. The antibodies raised against the sperm specific antigens have proved to be extremely effective at reducing sperm-egg interaction in vitro; fertility trials in sub-human primates would eventually prove the effectiveness of the sperm antigens in terms of contraceptive efficacy.     

Adoption of fertility limitation in an American frontier population: An analysis and simulation of socio‐religious subgroups

Abstract

This paper investigates a late nineteenth‐century fertility transition in a predominantly Mormon population of the western United States. A unique set of longitudinal data composed of 31,500 computerized family genealogies is drawn upon to examine a number of problems identified in reappraisals of fertility transition research (Caldwell, 1981; Freedman, 1979). Four subcohorts, differentiated by religious commitment and exposure to urban influences, are examined over the course of the transition. The study presents traditional analyses of subcohort CEB levels, period MTFR's, and m values (Coale and Trussell, 1974) and focuses on a macrosimulation of the fertility transition within the population (Bongaarts, 1976). Despite wide subcohort variation in cross‐sectional levels of fertility over time, simulation results suggest a similar absolute longitudinal decline in fertility levels, parity at which contraception was initiated, and maximum birth parities for all four subcohorts. The implications of these results for future analyses and the desirability of individual level data are discussed.     

Identification of AFLP markers linked to the male fertility restorer gene of CMS (Moricandia arvensis) Brassica juncea and conversion to SCAR marker

We have developed a cytoplasmic male sterile (CMS) line of Brassica juncea through somatic hybridization with Moricandia arvensis and introgressed the fertility restorer gene into B. juncea. This fertility restorer locus is unique in that it is capable of restoring male fertility to two other alloplasmic CMS systems of B. juncea. As a first step toward cloning of this restorer gene we attempted molecular tagging of the Rf locus using the amplified fragment length polymorphism (AFLP) technique. A BC₁F₁ population segregating for male sterility/fertility was used for tagging using the bulk segregant analysis method. Out of 64 primer combinations tested in the bulks, 5 combinations gave polymorphic amplification patterns. Further testing of these primers in individual plants showed four amplicons associated with the male fertility trait. Polymorphic amplicons were cloned and used for designing SCAR primers. One of the SCAR primers generated amplicons mostly in the fertile plants. Linkage analysis using MAPMAKER showed two AFLP and one SCAR markers linked to the male fertility gene with a map distance ranging from 0.6 to 2.9 cM. All the markers are located on one side of the Rf locus.     

A dynamic population model for tsetse (Diptera: Glossinidae) area-wide integrated pest management

A spatial model of tsetse (Glossina palpalis ssp. and G. pallidipes) life cycle was created in FORTRAN, and four control measures [aerial spraying of non-residual insecticides, traps and targets, insecticide-treated livestock (ITL) and the sterile insect technique] were programmed into the model to assess how much of each of various combinations of these control tactics would be necessary to eradicate the population. The model included density-independent and -dependent mortality rates, temperature-dependent mortality, an age-dependent mortality, two mechanisms of dispersal and a component of aggregation. Sensitivity analyses assessed the importance of various life history features and indicated that female fertility and factors affecting survivorship had the greatest impact on the equilibrium of the female population. The female equilibrium was likewise reduced when dispersal and aggregation were acting together. Sensitivity analyses showed that basic female survivorship, age-dependent and temperature-dependent survivorship of adults, teneral-specific survivorship, daily female fertility, and mean temperature had the greatest effect on the four applied control measures. Time to eradication was reduced by initial knockdown of the population and due to the synergism of certain combinations of methods [e.g., traps-targets and sterile insect technique (SIT); ITL and SIT]. Competitive ability of the sterile males was an important parameter when sterile to wild male overflooding ratios were small. An aggregated wild population reduced the efficiency of the SIT, but increased it with increased dispersal. The model can be used interactively to facilitate decision making during the planning and implementation of operational area-wide integrated pest management programs against tsetse.     

Restoration of Insular Ecosystems: Control of Feral Goats on Aldabra Atoll, Republic of Seychelles

The control of feral goats (Capra hircus) was studied on Aldabra Atoll, Republic of Seychelles, from October 1993 to May 1994 and November 1994 to May 1995. A total of 832 goats was killed on Aldabra using the Judas goat technique and traditional hunting methods. Twenty-eight goats equipped with radio transmitters (Judas goats) were used to locate and kill other feral goats. The remnant goat populations on Ile Picard (n=13) and Ile Malabar (n=19) were eradicated during the first season. On Grande Terre, a total of 798 (374 M : 424 F) goats were killed. Mean group size was 3.2 with a range of 1–20. Judas goat hunting became increasingly important over time with 18.0% (n=85) of goats killed in the presence of Judas goats in the first season compared to 42.3% (n=126) of goats killed during the second season. The overall kill rate for the project was almost 2 times greater for Judas goat hunting (0.61 goats killed/h) than traditional hunting (0.32 goats killed/h). The home range size of each Judas goat and the number of goats killed in association with it was significantly related. Using the Leslie–Davis removal method of population estimation, 84 goats were estimated to remain on all of Grande Terre at the end of thebreak project. This revised version was published online in July 2006 with corrections to the Cover Date.     

Demographics of Black Vultures in North Carolina

Abstract: Understanding the contributions of vital rates to species population growth is critical to developing new management protocols. We constructed a model population for black vultures (Coragyps atratus) in North Carolina, USA, based on demographic data from a 14-year study. The model population was similar in stage structure to the reference population, and adult survival was the primary contributor to the annual rate of increase (10.6%). We suggest that the North Carolina black vulture population is experiencing high rates of survival and fertility, potentially breeding at an age younger than previously assumed, and growing rapidly.     

Demography in relation to population density in two herbivorous marsupials: testing for source–sink dynamics versus independent regulation of population size

We compared demography of populations along gradients of population density in two medium-sized herbivorous marsupials, the common brushtail possum Trichosurus vulpecula and the rufous bettong Aepyprymnus rufescens, to test for net dispersal from high density populations (acting as sources) to low density populations (sinks). In both species, population density was positively related to soil fertility, and variation in soil fertility produced large differences in population density of contiguous populations. We predicted that if source–sink dynamics were operating over this density gradient, we should find higher immigration rates in low-density populations, and positive relationships of measures of individual fitness—body condition, reproductive output, juvenile growth rates and survivorship—to population density. This was predicted because under source–sink dynamics, immigration from high-density sites would hold population density above carrying capacity in low-density sites. The study included 13 populations of these two species, representing a more than 50-fold range of density for each species, but we found that individual fitness, immigration rates and population turnover were similar in all populations. We conclude that net dispersal from high to low density populations had little influence on population dynamics in these species; rather, all populations appeared to be independently regulated at carrying capacity, with a balanced exchange of dispersers among populations. These two species have suffered recent reductions in range, and they are ecologically similar to other species that have declined to extinction in inland Australia. It has been argued that part of the cause of the vulnerability of species like these is that they exhibit source–sink dynamics, and disturbance to source habitats can therefore cause large-scale population collapses. The results of our study argue against this interpretation.     

The effects of spiromesifen on life history traits and population growth of two-spotted spider mite (Acari: Tetranychidae)

Laboratory bioassays were conducted to evaluate the effects of spiromesifen on gross fecundity, gross fertility, net fertility and population growth of two-spotted spider mite (Tetranychus urticae Koch) after treatments with four acaricide concentrations: 180 mg/l, i.e. maximum recommended concentration for use in glasshouses against spider mites, 18, 1.8, and 0.18 mg/l, i.e. concentration discriminative for eggs and immatures in preliminary studies which produced 100% mortality of these stages. Quiescent female deutonymphs were treated in the first assay, and young pre-ovipositing females in the second and third, in which exposure lasted 6 h and 20 h, respectively. In the first assay, the 180, 18, and 1.8 mg/l concentrations significantly reduced gross fecundity (61–85%), gross fertility (64–87%) and net fertility (85–94%) of the surviving females. In the second one, only the highest concentration achieved a significant statistical reduction in gross fecundity (52%), gross fertility (67%) and net fertility (84%). In the third assay, fecundity and fertility reduction under the two highest concentrations was 98–99% and 93–98%, whereas it was 50–74% under the 1.8 mg/l concentration, and statistically different from control values. In all three trials, treatments with 180, 18, and 1.8 mg/l concentrations significantly reduced the instantaneous rate of increase. In the third assay, treatments with the two highest concentrations caused population decline. Sublethal activity of the 0.18 mg/l concentration was not found in any assay to be statistically significant. Sublethal effects of spiromesifen and its impact on T. urticae management are discussed.     

The effects of herbivory and soil fertility on the growth patterns of <Emphasis Type="Italic">Quercus serrata</Emphasis> and <Emphasis Type="Italic">Q. crispula</Emphasis> saplings at the shoot and individual levels

We investigated the combined effects of herbivore damage and soil fertility on shoot growth patterns of Quercus serrata and Q. crispula saplings at both the shoot and individual levels. Saplings were grown in herbivore-damaged or undamaged areas of the greenhouse with the two fertilization treatment levels, low or high. We measured the leaf area loss, number of flushes, length of extension units (EUs; the first vs the higher), number of leaves on each individual, and number of EUs. At the shoot level, the leaf area loss at high soil fertility was significantly greater than that at low soil fertility among the highest EUs of Q. serrata, while this difference was not significant in Q. crispula, suggesting that effect of soil fertility on leaf area loss is species-specific. Furthermore, herbivore damage was associated with a significant increase in the number of EUs and a reduction in the length of the higher EUs under both soil fertility treatments, although saplings had a tendency to produce significantly more flushes and longer individual EUs under the high soil fertility. At the individual level, herbivore-damaged saplings exhibited a significant increase in leaf numbers; however, the total length of the EUs in Q. serrata or Q. crispula was not significantly affected by herbivore damage, regardless of soil fertility. These results suggest that Q. serrata and Q. crispula saplings produce shorter EUs in response to herbivore damage in order to reduce the cost of mechanical support and spread the risk for any subsequent herbivore damage.     

Immunocontraception in Wild Horses: One Inoculation Provides Two Years of Infertility

ABSTRACT ABSTRACT Previous studies reported one year of contraception associated with a 1-injection porcine zona pellucida (PZP) vaccine. We have subsequently determined contraceptive effectiveness of a presumptive 1-injection, 2-year-duration PZP vaccine in free-roaming wild horses (Equus caballus) in Nevada, USA. In January 2000, we captured, freeze-branded, treated, and subsequently released 96 adult females that received 1) a primary dose of vaccine emulsion consisting of aqueous PZP and Freund's Complete Adjuvant, and 2) booster doses of PZP and adjuvant in controlled-release polymer pellets. We determined PZP release characteristics of pellets in vitro, prior to field use. We determined reproductive success in treated and untreated females through October 2004 via measurement of estrone sulfate and progesterone metabolites in fresh feces collected from the ground and by twice-annual foal counts. Among treated females, annual reproductive success from 2001 though 2004 sequentially was 5.9%, 14.0%, 32.0%, and 47.5%. Untreated females showed average reproductive success of 53.8 ± 1.3% across this period. This study revealed that: 1) PZP acted as an effective contraceptive for 2 years posttreatment; 2) some residual contraceptive effect remained in year 3; and 3) fertility returned to control levels by year 4 posttreatment. It appears that controlled-release technology can replace both the second(1-month) and annual booster injection of PZP vaccine, thereby decreasing cost and increasing efficiency of use of this vaccine in wild horse management.