The status of fertility control for rodents-recent achievements and future directions

Male animal sterilization: history, current practices, and potential methods for replacing castration

Sterilization and castration have been synonyms for thousands of years. Making an animal sterile meant to render them incapable of producing offspring. Castration or the physical removal of the testes was discovered to be the most simple but reliable method for managing reproduction and sexual behavior in the male. Today, there continues to be global utilization of castration in domestic animals. More than six hundred million pigs are castrated every year, and surgical removal of testes in dogs and cats is a routine practice in veterinary medicine. However, modern biological research has extended the meaning of sterilization to include methods that spare testis removal and involve a variety of options, from chemical castration and immunocastration to various methods of vasectomy. This review begins with the history of sterilization, showing a direct link between its practice in man and animals. Then, it traces the evolution of concepts for inducing sterility, where research has overlapped with basic studies of reproductive hormones and the discovery of testicular toxicants, some of which serve as sterilizing agents in rodent pests. Finally, the most recent efforts to use the immune system and gene editing to block hormonal stimulation of testis function are discussed. As we respond to the crisis of animal overpopulation and strive for better animal welfare, these novel methods provide optimism for replacing surgical castration in some species.

Impacts of climate change and human activities on three Glires pests of the Qinghai-Tibet Plateau

BACKGROUND

The range of Glires is influenced by human activities and climate change. However, the extent to which human activities and environmental changes have contributed to this relationship remains unclear. We examined alterations in the distribution changes and driving factors of the Himalayan marmot, plateau pika, and plateau zokor on the Qinghai-Tibet Plateau (QTP) using the maximum entropy (MaxEnt) model and a geographical detector (Geodetector).

RESULTS

The MaxEnt model showed that the contribution rates of the human footprint index (HFI) to the distribution patterns of the three types of Glires were 46.70%, 58.70%, and 59.50%, respectively. The Geodetector results showed that the distribution pattern of the Himalayan marmot on the QTP was influenced by altitude and the normalized difference vegetation index (NDVI). The distribution patterns for plateau pikas and plateau zokors were driven by HFI and NDVI. Climate has played a substantial role in shaping suitable habitats for these three Glires on the QTP. Their suitable area is expected to decrease over the next 30-50 years, along with their niche breadth and overlap. Future suitable habitats for the three Glires tended to shift toward higher latitudes on the QTP.

CONCLUSION

These findings underscore the impacts of environmental and human factors on the distribution of the three Glires on the QTP. They have enhanced our understanding of the intricate relationships between Glires niches and environments. This can aid in identifying necessary interventions for developing effective early warning systems and prevention strategies to mitigate Glires infestations and plague epidemics on the QTP. © 2024 Society of Chemical Industry.

Effects of an Anti-Fertility Product on Reproductive Structures of Common Vole Males and Residues of Compounds

Some rodent species cause significant damage to agriculture and forestry, and some can transmit pathogens to humans and livestock. The common vole (Microtus arvalis) is widespread in Europe, and its population outbreaks have resulted in massive crop loss. Bait-based fertility control could contribute to rodent pest management. Bait containing 4-vinylcyclohexene diepoxide (VCD) and triptolide (TP), registered as ContraPest®, was delivered to male common voles for 14 or 28 consecutive days. The effects on reproductive structures and residues in the liver and testes were assessed. There was no effect on testis weight, sperm viability, sperm motility and oxidative stress in sperm cells. Results regarding the mitochondrial membrane potential of sperm, DNA fragmentation and progressively motile sperm cells were inconclusive. However, there was an increase in morphological sperm defects in voles treated for 14/28 days and fewer normal sperm cells in voles treated for 28 days. There were no TP residues in the testes, few and low TP residues and no VCD residues in liver tissues, making considerable secondary exposure to non-target species unlikely. Treatments with VCD + TP seemed to have minor effects on the reproductive organs of males. Further studies should evaluate the effect of VCD + TP on females and on the reproductive success of common voles and other pest rodent species.

THE EFFECT OF 4-VINYLCYCLOHEXENE DIEPOXIDE ON FEMALE NUTRIA (MYOCASTOR COYPUS) FERTILITY IN CAPTIVITY-A PILOT STUDY

The nutria (Myocastor coypus) is a globally widespread invasive species. Attempts to eradicate nutria by shooting, poisoning, and trapping have been mostly unsuccessful, leading to calls for the development of new control methods. The compound 4-vinylcyclohexene diepoxide (VCD) is known to cause follicular atresia in mammals and may control conception when administered orally. It was hypothesized that VCD administered PO will cause follicular destruction in female nutria. VCD (250 mg/kg PO) was administered or coconut oil, as a control, to five nutria females each for 12 d. Sixty days following VCD exposure, males were introduced to the females. Over the following 7 mon, the effect of VCD on nutria fertility was assessed by conducting ultrasound monitoring to determine pregnancy status and measuring blood serum progesterone and estradiol levels. Finally, after performing ovariectomies, viable follicles were counted on histologic ovarian cortical sections. It was found that the female estrous cycles became synchronized, suggesting a Whitten effect in this species. Also, an increase in the females' serum progesterone levels following the introduction of males occurred, suggesting a male presence effect. Orally administered doses of 250 mg/kg VCD for 12 d had no significant effect on nutria pregnancy rates or on the number of follicles in the ovaries examined. Further studies, using a higher dose or longer administration period, are necessary to conclude whether orally administered VCD can be used as a contraceptive agent for nutria.

A strategy to improve rodent control while reducing rodenticide release into the environment

In addition to having a negative impact on the health of people and domestic animals, rodents often cause enormous damage to the environment by disrupting natural biodiversity. The negative impacts of rodents in urban and rural areas have required intensive use of rodentcides in spite of the proven risk of secondary poisoning of non-target predators and scavengers. Continuous and intensive use of rodenticides has led to environmental pollution through their retention in the environment. Commensal rodents are predominantly managed with anticoagulant rodenticides, which are very persistent in the environment and move up the food chain and accumulate in the bodies of predators and scavengers. Generally, the use of anticoagulant rodenticides continues, and there is a need to take appropriate measures to reduce their harmful impact. The efficacy of second generation anticoagulants (bromadiolone, difenacoum and brodifacoum), combined either mutually or with chlorophacinone at reduced doses (0.001 % and 0.0008 %), in controlling brown rats (Rattus norvegicus) was tested in a four-day no-choice feeding test. Combinations of second generation anticoagulants were more effective than the combination of chlorophacinone and second generation anticoagulants. The results indicate that combinations of different anticoagulants at multifold lower doses than the standard may provide a successful tool for brown rat control and a more environment-friendly method of rodent control and protection of non-target animals.

Antifertility effects of quinestrol in male lesser bandicoot rat, Bandicota bengalensis, and potential in managing rodent population under field conditions

Integrating fertility control techniques using steroid hormones after lethal control can help reduce post control rebuildup of rodent populations. The current study is the first to assess the antifertility effects of quinestrol in male lesser bandicoot rat, Bandicota bengalensis which is the predominant rodent pest species in Southeast Asia. Rats in different groups were fed bait containing 0.00%, 0.01%, 0.02%, and 0.03% quinestrol for 10 days in laboratory and evaluated immediately, and 15, 30, and 60 days after treatment discontinuation for effect on reproduction and other antifertility parameters. Effect of 0.03% quinestrol treatment for 15 days was also observed in managing rodent populations in groundnut crop fields. Treatment resulted in average consumption of 19.53 ± 1.80, 67.63 ± 5.50, and 246.67 ± 1.78 mg/kg bwt active ingredient by three treated groups of rats, respectively. No reproduction was observed in female rats mated with male rats treated with 0.03% quinestrol, even 30 days after cessation of treatment. Post-mortem examination showed a significant (P < 0.0001) effect of treatment on organ weights (testis, cauda epididymis, seminal vesicles, and prostate gland) and different sperm parameters (sperm motility, sperm viability, sperm count, and sperm abnormality) in the cauda epididymal fluid with partial reversibility after 60 days. A significant (P < 0.0001) effect of quinestrol on the histomorphology of testis and cauda epididymis was observed, suggesting its effect on spermatogenesis. Affected cell association and cell count in seminiferous tubules did not fully recover within 60 days of stopping treatment. Evaluation of the effects of quinestrol treatment in groundnut fields showed greater reductions in rodent activity in fields treated with 2% zinc phosphide followed by 0.03% quinestrol treatment as compared to fields treated with 2% zinc phosphide alone. Research concludes that quinestrol has the potential to reduce fecundity and post control rebuildup of B. bengalensis populations, but long-term studies of the effectiveness of quinestrol under large-scale field conditions are needed to use it as part of an integrated pest control program for rodents.

Antifertility effects of EP-1 (quinestrol and levonorgestrel) on Pacific rats (Rattus exulans)

Pest rodents pose a serious threat to island biodiversity. Fertility control could be an alternative approach to control the impact of rodents on these islands. In this study, we examined the antifertility effects of EP-1 baits containing quinestrol (E) and levonorgestrel (P) using a dose of 50 ppm E and P at three different ratios (E:P ratio = 1:2, 1:1, and 2:1) on Pacific rats (Rattus exulans) in the Xisha Islands, Hainan, China. Compared to the control group, all animals in EP-1 treatment groups showed significantly decreased food intake and body weight. In treated males, there were obvious abnormalities in testis structure and a significant decrease of relative seminal vesicle weight, but no significant effect on relative uterine and ovarian weights (g kg-1 body weight), or ovarian structure in females. Adding 8% sucrose to the original 50-ppm baits (E:P ratio = 1:1) significantly increased bait palatability for males and females. This dose induced uterine edema and abnormalities of ovarian structure in females but had no significant negative effect on the relative testis, epididymis, and seminal vesicle weights (g kg-1 body weight) or sperm density in males. In summary, 50-ppm EP-1 (1:1) baits have the potential to disrupt the fertility of females, and 8% sucrose addition to the EP-1 baits (E:P ratio = 1:1) could improve bait palatability. This dose disrupted the testis structure in males. Future studies are needed to improve bait acceptance and assess the antifertility effects of EP-1 (1:1) on Pacific rats in captive breeding trials and under field conditions.

Developing fertility control for rodents: a framework for researchers and practitioners

Fertility control is often heralded as a humane and effective technique for management of overabundant wildlife, including rodents. The intention is to reduce the use of lethal and inhumane methods, increase farm productivity and food security as well as reduce disease transmission, particularly of zoonoses. We developed a framework to guide researchers and stakeholders planning to assess the effectiveness of a potential contraceptive agent for a particular species. Our guidelines describe the overarching research questions which must be sequentially addressed to ensure adequate data are collected so that a contraceptive can be registered for use in broad-scale rodent management. The framework indicates that studies should be undertaken iteratively and, at times, in parallel, with initial research being conducted on (1) laboratory-based captive assessments of contraceptive effects in individuals; (2) simulation of contraceptive delivery using bait markers and/or surgical sterilization of different proportions of a field-based or enclosure population to determine how population dynamics are affected; (3) development of mathematical models which predict the outcomes of different fertility control scenarios; and (4) implementation of large-scale, replicated trials to validate contraceptive efficacy under various management-scale field situations. In some circumstances, fertility control may be most effective when integrated with other methods (e.g. some culling). Assessment of non-target effects, direct and indirect, and the environmental fate of the contraceptive must also be determined. Developing fertility control for a species is a resource-intensive commitment but will likely be less costly than the ongoing environmental and economic impacts by rodents and rodenticides in many contexts.

Controlling Effects of Nanocomposite Sterilant ND-1 on the Growth of Wild Populations of Midday Gerbil (Meriones meridianus)

Grassland is not only an important part of the terrestrial ecosystem with multiple ecological functions, but also an important base for Chinese herdsmen to produce and live. However, the occurrence and spread of rodent infestation reduces the biodiversity and productivity of grassland ecosystems. It also severely threatens human life, health, and biosecurity through disease transmission. In this study, we explored the ability of the nanocomposite sterilant ND-1 to control grassland rodent populations. Semi-closed experimental and control plots were established in the desert area of Alashan, Inner Mongolia, China. In spring 2018, the nanocomposite sterile ND-1 (Nongda-1) was introduced once, and the control effect of ND-1 on the growth of the wild population of midday gerbils was measured for two years. We show that ND-1 significantly reduced the population of midday gerbils in the experimental area, with a negative population growth rate. In addition, in the second year, the ratio of female midday gerbils to sub-adults in the experimental area was significantly lower than that in the control area, which resulted in a significant difference in the sex ratio of midday gerbils. There were significantly fewer females than males, and the population growth of midday gerbils in the experimental area was significantly inhibited. ND-1 had no significant effect on the home range of midday gerbils, and sterile individuals continued to occupy the home range and consume resources. Therefore, ND-1 reduced the number of female midday gerbils during the breeding period and the sex ratio and population density and altered the age structure of the wild population. Additionally, competition between sterile and normal individuals had a significant control effect on the growth of wild populations. Our studies demonstrate the significance of ND-1 in the sustainable control of grassland rodent pests, with the potential for limiting grassland rodent damage in the future.

Immunogenicity and contraceptive efficacy of plant-produced putative mouse-specific contraceptive peptides

Rodent population control through contraception requires species-specific oral contraceptive vaccines. Therefore, in this study, we produced putative mouse-specific contraceptive peptides, mZP2 (from oocyte) and mIzumo1 (from sperm), in plants using Agrobacterium-mediated transient expression. Peptides were produced separately in Nicotiana benthamiana using constructs encoding antigens containing three copies of each peptide. We also determined the immunogenicity and contraceptive effects of the plant-produced antigens in female BALB/c mice. Mice immunized subcutaneously with a relatively low amount of antigen (5 µg/dose of each peptide in a mixture) showed systemic immune responses against mZP2-3 and mIzumo1-3 antigens. Moreover, the mean litter size of mice treated with the plant-produced antigens was reduced by 39% compared to that of the control mice. Notably, there was a significant negative correlation between the number of pups born and individual antibody levels against both antigens. Immunofluorescence assays demonstrated the binding of induced antibodies to the oocytes of BALB/c and wild-type mice in vivo and in vitro, respectively. Our study demonstrate the feasibility of producing small contraceptive peptides in plants that can be further used to develop oral contraceptive vaccines against mouse populations.

Paper mulberry leaves as a potential sterilant: evidence from Microtus fortis-a laboratory study

Introduction

The Yangtze vole (Microtus fortis) is a small herbivorous rodent that usually causes damage to crops and forests in China. Various measures were used to control their population including chemical rodenticides. However, rodenticides may cause secondary damage to the environment and the ecosystem. Therefore, the development of new rodent sterilants is urgent. Considering that some compounds of paper mulberry leaves have been verified that can inhibit the biosynthesis of sexual hormone, we aimed to explore the antifertility effect of paper mulberry leaves on M. fortis.

Methods

In this study, voles were divided into three groups including a male group, a female group, and a breeding group, and paper mulberry leaves were added into basal fodder of voles maintained in laboratory, of which the proportion of leaf weight was 50%. In each group, voles were fed with mixed fodder as treatment (BP) and voles were fed with basal fodder as contrast (CK).

Results and discussion

After feeding for more than 1 month, the results indicated that paper mulberry leaves attracted voles to feed, but inhibited their growth and reproduction. Since the second week, food intakes of BP have been significantly higher than CK (p< 0.05). However, weights of voles in male and female groups were 72.283 ± 7.394 g and 49.717 ± 2.278 g in the fifth week, and both were significantly reduced compared with their original weight (p< 0.05). Meanwhile, testicular volumes of male voles fed with BP were significantly smaller than CK (former: 318.000 ± 44.654 mm³, latter: 459.339 ± 108.755 mm³); the testosterone level, sperm number, and vitality of BP were obviously weaker than CK. Female uteruses and oophoron of BP grew slower, and the organ coefficients of uterus and oophoron fed BP were both significantly lower than CK (p< 0.05). The first reproduction of BP couple voles spent 45 days, while CK spent only 21 days. These results suggest that paper mulberry leaves could be the potential resource to produce sterilants to control rodent populations by delaying their sexual growth and reproduction. If it was practical, the apparent advantages of paper mulberry are that it is an abundant resource and the inhibitory effect could be effective in both male and female individuals. Our conclusion also supports the transformation of rodent management from lethal management to fertility control, which would be more ecologically friendly to agriculture and the ecosystem.

Antireproductive changes instigated by efficient drug delivery via papaya seed chloroform extract-based nanoparticles in male rat Bandicota bengalensis

Anti-reproductive potential of papaya seed chloroform extract-based solid lipid nanoparticles (PSCEN) was investigated for the first time in lesser bandicoot rat, Bandicota bengalensis. Mature male rats (n = 30 per group) were fed bait (loose mixture of cracked wheat, powdered sugar, and groundnut oil in the ratio 88:10:2) containing two different concentrations of PSCEN (5% and 10%) in a bi-choice condition for 15 days with one group as vehicle control. The ingestion of active ingredient in 15 days treatment was significantly (P ≤ 0.05) higher by rats treated with 10% PSCEN (39.17-58.70 g/kg body weight) as compared to rats treated with 5% PSCEN (21.30-33.23 g/kg body weight). A dose dependent significant (P ≤ 0.05) decrease was observed in the level of testosterone, FSH, LH and GnRH in plasma of treated rats. A significant (P ≤ 0.05) decrease was also observed in level of total soluble proteins, total lipids, phospholipids and cholesterol in both plasma and testicular tissue, and level of 17β-HSD and 3β-HSD in testicular tissue indicating anti-reproductive effects of PSCEN treatment. There was observed significant (P ≤ 0.05) effect of treatment on histomorphology of testis and cauda epididymis in the form of reduced tubular diameter, germinal epithelial thickness, number of germ cells and dissociation of epithelial cycle in seminiferous tubules, and reduced tubular diameter, increased epithelial thickness, vacuolization, loose contact of principle cells and reduced number of spermatozoa in the cauda epididymal tubules. Maximum antifertility effect was observed with 10% PSCEN treatment, which was not reversed upto 105 days of treatment withdrawal indicating long-term efficacy. The current investigation suggests the use of PSCEN in the management of reproduction of B. bengalensis by exerting influence on testicular and cauda epididymal functions and biochemical parameters.

Intergenerational response to sperm competition risk in an invasive mammal

Studies of socially mediated phenotypic plasticity have demonstrated adaptive male responses to the 'competitive' environment. Despite this, whether variation in the paternal social environment also influences offspring reproductive potential in an intergenerational context has not yet been examined. Here, we studied the descendants of wild-caught house mice, a destructive pest species worldwide, to address this knowledge gap. We analysed traits that define a 'competitive' phenotype in the sons of males (sires) that had been exposed to either a high-male density (competitive) or high-female density (non-competitive) environment. We report disparate reproductive strategies among the sires: high-male density led to a phenotype geared for competition, while high-female density led to a phenotype that would facilitate elevated mating frequency. Moreover, we found that the competitive responses of sires persisted in the subsequent generation, with the sons of males reared under competition having elevated sperm quality. As all sons were reared under common-garden conditions, variation in their reproductive phenotypes could only have arisen via nongenetic inheritance. We discuss our results in relation to the adaptive advantage of preparing sons for sperm competition and suggest that intergenerational plasticity is a previously unconsidered aspect in invasive mammal fertility control.

Oral and Subcutaneous Immunization with a Plant-Produced Mouse-Specific Zona Pellucida 3 Peptide Presented on Hepatitis B Core Antigen Virus-like Particles

A short mouse-specific peptide from zona pellucida 3 (mZP3, amino acids 328-342) has been shown to be associated with antibody-mediated contraception. In this study, we investigated the production of mZP3 in the plant, as an orally applicable host, and examined the immunogenicity of this small peptide in the BALB/c mouse model. The mZP3 peptide was inserted into the major immunodominant region of the hepatitis B core antigen and was produced in Nicotiana benthamiana plants via Agrobacterium-mediated transient expression. Soluble HBcAg-mZP3 accumulated at levels up to 2.63 mg/g leaf dry weight (LDW) containing ~172 µg/mg LDW mZP3 peptide. Sucrose gradient analysis and electron microscopy indicated the assembly of the HBcAg-mZP3 virus-like particles (VLPs) in the soluble protein fraction. Subcutaneously administered mZP3 peptide displayed on HBcAg VLPs was immunogenic in BALB/c mice at a relatively low dosage (5.5 µg mZP3 per dose) and led to the generation of mZP3-specific antibodies that bound to the native zona pellucida of wild mice. Oral delivery of dried leaves expressing HBcAg-mZP3 also elicited mZP3-specific serum IgG and mucosal IgA that cross-reacted with the zona pellucida of wild mice. According to these results, it is worthwhile to investigate the efficiency of plants producing HBcAg-mZP3 VLPs as immunogenic edible baits in reducing the fertility of wild mice through inducing antibodies that cross-react to the zona pellucida.

Synergistic effects of EP-1 and ivermectin mixture (iEP-1) to control rodents and their ectoparasites

BACKGROUND

Ectoparasites of rodents play significant roles in disease transmission to humans. Conventional poisoning potentially reduces the population densities of rodents, however, they may increase the ectoparasite loads on the surviving hosts. EP-1 has been shown to have anti-fertility effects on many rodent species, while ivermectin is effective in controlling ectoparasites. In this study, we examined the combined effects of EP-1 and ivermectin mixture (iEP-1) baits on rodents and their corresponding flea/tick loads.

RESULTS

In males, the weight of testis, epididymis, and seminiferous vesicle were reduced to less than 33%, 25%, and 17%, respectively, compared to the control group following administration of iEP-1 for 7 days. The weight of the uterus increased by approximately 75%. After 5 days of iEP-1 intake, all ticks were killed, whereas 94% of fleas on mice died after 3 days of bait intake. In the field test near Beijing, the flea index was reduced by more than 90% after 7 days of iEP-1 bait delivery. In a field test in Inner Mongolia, the weights of testis, epididymis, and seminiferous vesicle were significantly reduced by 27%, 32%, and 57%, respectively, 2 weeks after iEP-1 bait delivery. Approximately 36% rodents exhibited obvious uterine oedema accompanied by a weight increase of about 150%. The flea index was reduced by over 90%.

CONCLUSION

Our results indicated that iEP-1 is a promising treatment for reducing the abundance of both small rodents and their ectoparasites; this will be effective for managing rodent damage and transmission of rodent-borne diseases associated with fleas and ticks. © 2022 Society of Chemical Industry.

The reversible effects of gossypol toxicity on male pigeons' reproductive performance

Background and Aim

Gossypol, a cotton seed derivative, is well known for its reversible antifertility in male reproduction across species. Its antifertility and reversibility effects on male reproductive function vary among species in dose-and time-dependent manners. In this study, the antifertility potential of gossypol in pigeons was evaluated for the first time to determine whether it might be used as a dietary supplement for pigeon population control.

Materials and Methods

Male pigeons were assigned into three experimental groups: The gossypol-treated group (n = 12), the sham control group (n = 6), and the negative control group (n = 6). There were two experimental periods: A gossypol-feeding period of 28 days and a gossypol-free period of 28 days. During the gossypol-feeding period, birds in the gossypol-treated group were fed 4 mg of gossypol extract per day. Birds in the sham control group were fed 0.5 mL of mixed ethanol and sunflower oil, while those in the negative control group were fed 0.5 mL of phosphate buffer saline. After the gossypol-feeding phase was completed, all remaining pigeons in all groups continued to receive their regular diet for an additional 28 days (gossypol-free phase). The body weight and semen quality of the birds in the experimental groups were compared to evaluate gossypol's antifertility effect.

Results

In the gossypol-treated group as compared to the control groups, the percentages of sperm motility and viability were significantly lower at 21 days, and the percentage of normal sperm morphology was significantly lower at 28 days during the gossypol-feeding period. After gossypol withdrawal, these antifertility effects were resumed and reached a comparable semen quality to the control groups within 14 days.

Conclusion

Gossypol supplementation (4 mg/day for 28 days) could lower male pigeons' reproductive performance in terms of sperm motility, viability, and sperm morphology. Such infertility was, however, reversible within 14 days after gossypol withdrawal without any side effects on the pigeons, suggesting its application as a safe contraceptive feeding for male pigeons.

A Systematic Review and Meta-Analysis of the Inhibitory Effects of Plant-Derived Sterilants on Rodent Population Abundance

Owing to their low minimal environmental risk and other ethical considerations, plant-derived sterilants are used to control rodent populations. However, the effects of plant-derived sterilants are not immediate, and their efficacy on rodent control is controversial, which negatively affects sterilant research and application. Here, a meta-analysis of the available literature was conducted to evaluate the effects of two plant-derived sterilants, triptolide and curcumol, on rodent populations. Using a random-effects and a fixed-effects model, we calculated the weighted mean difference (WMD) and relative risk (RR) and their corresponding 95% confidence intervals (95% CIs). After the application of plant-derived sterilants, the rodent population density tended to decrease. Three outcome-related measures in rodents, i.e., capture rate (RR = 0.31, 95% CI [0.20, 0.47]), pregnancy rate (RR = 0.49, 95% CI [0.40, 0.61]), and sperm survival rate (WMD = −17.53, 95% CI [−28.96, −6.06]), significantly decreased, as shown by a significant reduction of ovarian, uterine, and testicular organ coefficients. However, the number of effective rodent holes did not change significantly after the interventions, indicating that the studied sterilants did not directly eradicate the rodent populations. This study provides a theoretical basis for elucidating the inhibitory mechanisms of plant-derived sterilants on rodent populations and for the rational use of these sterilants.

Antifertility effects of levonorgestrel, quinestrol and their mixture (EP-1) on plateau zokor in the Qinghai-Tibetan Plateau

The plateau zokor (Eospalax baileyi Thomas, 1911) is a key species in the Qinghai-Tibetan Plateau ecosystem, and fertility control could be an ideal approach to manage populations of this subterranean species. In this laboratory study, we explored the effects of the mixture of levonorgestrel and quinestrol (EP-1, 1:2), quinestrol (E), and levonorgestrel (P) on the reproductive status of plateau zokors. Groups of five animals of each sex were treated with different concentrations of EP-1 (1, 5, and 10 mg/kg), E (0.33, 3.3, and 6.6 mg/kg), and P (0.67, 3.35, and 6.7 mg/kg) by oral gavage over 7 successive days and killed on day 15. Body mass reduction was observed in the EP-1 and E groups. EP-1 and E significantly reduced the weight of testis and epididymis at 10 and 3.3 mg/kg, respectively. Sperm count and motility were significantly reduced by 5 mg/kg EP-1 and 0.33 mg/kg E. The levels of serum testosterone, estradiol, luteinizing hormone, and follicle stimulating hormone were significantly reduced by 5 mg/kg EP-1 and 3.3 mg/kg E. EP-1 and E significantly reduced the uterine and ovarian weights at 10 and 3.3 mg/kg, respectively. In the plateau zokors, treatment with P had no influence on the reproductive status. These data demonstrate that EP-1 and E have an inhibitory effect on a range of reproductive parameters in the plateau zokors. Further assessment is required to determine the effects on breeding and recruitment in enclosure or field experiments. This article is protected by copyright. All rights reserved.

Reproductive responses of rice field rats (Rattus argentiventer) following treatment with the contraceptive hormones, quinestrol and levonorgestrol

The rice field rat, Rattus argentiventer, is a significant pest of rice in Southeast Asia. Fertility control methods have the potential to provide safe and effective alternatives to control methods that often include indiscriminate use of rodenticides or electric barriers. The aim of this laboratory study was to assess uptake of bait coated with different concentrations of the contraceptive hormones, quinestrol (E) and levonorgestrel (P), delivered alone and in combination (i.e. EP-1) and determine the short-term effects on reproductive parameters of adult male and female R. argentiventer. In Experiment 1, 2 concentrations of E, P, and EP-1 (10, 20 ppm) were fed to groups of wild-caught rats for 7 days. In females, both E and EP-1 induced uterine edema. In males, EP-1 reduced epididymis and seminal vesicle weights and lowered sperm motility. However, these responses were inconsistent due to low bait acceptance, especially with increasing concentrations. In Experiment 2, EP-1 (0, 20, 50, 100 ppm) was administered by oral gavage daily for 7 days to male R. argentiventer. There were significant reductions in epididymal and seminal vesicle weights for all oral doses of EP-1, in sperm counts for the 50 ppm dose, and in sperm motility for the 20 and 50 ppm doses compared to the control group. To select the optimum dose of EP-1, we must address the poor acceptance of contraceptive-coated baits by rice field rats. Further research is required to improve the palatability of EP-1 and to test its uptake under field conditions.