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

Abstract

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 wildcaught 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.

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

“…Since the report by Zhang et al ., 13 the anti‐fertility effect of EP‐1 on wild rodents has been confirmed by many laboratory and field studies 15,17–19,21,36,38–40 . In this study, we found EP‐1 and iEP‐1 significantly reduced the weight of testis and epididymis of male long‐tailed hamster, Mongolian gerbils, and mid‐day gerbils, increased the weight of the uterus while inducing uterus oedema, similar to previous studies.…”

“…In 2004, EP‐1 was found to reduce fertility of Brandt's Vole ( Lasiopodomys brandtii ), grey hamster ( Cricetulus migratorius ) and mid‐day gerbils ( Meriones meridianus ) under laboratory condition 13 . A series of subsequent studies confirmed the anti‐fertility effect of EP‐1 in many rodent species in China, 14–19 Tanzania, 20 and Indonesia 21 . EP‐1 degrades rapidly in the natural environment, 22–24 and showed a small negative effect on birds in the Qinghai‐Tibetan Plateau 25 .…”

“…13 A series of subsequent studies confirmed the anti-fertility effect of EP-1 in many rodent species in China, [14][15][16][17][18][19] Tanzania, 20 and Indonesia. 21 EP-1 degrades rapidly in the natural environment, [22][23][24] and showed a small negative effect on birds in the Qinghai-Tibetan Plateau. 25 Under natural conditions, the anti-fertility effect of a single baiting of EP-1 could persist for about 3 to 4 months on rodents.…”

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

“…2021), because fertility compounds could alter the palatability of bait (Stuart et al . 2021). The treatment groups in our study were treated by oral gavage, and therefore, we argue that the adverse effects of the contraceptive hormones may have affected the appetite of the animals.…”

Fertility control of rodent pests: recent developments from lab to field

“…Professor Zhang has also attracted research funding to support recent collaborative studies in Tanzania, Zambia, Ethiopia and Indonesia. Some of the papers (Imakando et al 2021;Selemani et al 2021;Stuart et al 2021) in this special issue reflect those collaborative efforts, and additional research efforts by other Chinese researchers. One example in this issue is the first laboratory study of the effects of E, P and EP-1 on the subterranean rodent, the plateau zokor (Eospalax baileyi), a key native species competing with livestock on the Qinghai−Tibet plateau (Kang et al 2022).…”