Sex Hormone Dynamics and Pseudopregnancy during the Breeding Season in the Japanese Red Fox (Vulpes vulpes japonica)

Abstract

Fecal and blood concentration of estradiol-17β(E₂) and progesterone(P₄) were measured in 2 female, adult Japanese red foxes (Vulpes vulpes japonica) kept in a zoo. As the result, the blood E₂ level recognized the peak only 1 time in January, and it rapidly decreased afterwards. Blood and fecal P₄ level increased rapidly in conjunction with blood E₂ level, and maintained relatively high level for about 2 months after a sharp peak and gradually decreasing. The swelling of the vulva would be recognized in the end of January in which there was the rise in blood E₂ value, and it continued for about 1 week. In addition, the swelling of the mammary gland would be observed in the end of February, and the depilation around the mammary gland would be observed in the beginning of March. After that, secretion of milk-like liquid was observed. From the hormonal dynamics, it was confirmed that the Japanese red foxes had the same characteristics as other canids such as that it was monoestrus and that the luteal phase continued as in the pregnancy regardless of pregnancy and non-pregnancy. In addition, from the latter half of the P₄ level rise period, behavior similar to pseudopregnancy seen in dogs was observed, suggesting that pseudopregnancy may also be seen in Japanese red foxes. On the significance of the pseudopregnancy of foxes, the relevance to the helpers in rearing cubs was considered.