Estimation of the fertility rates of Japanese wild boars ( Sus scrofa leucomystax ) using fetuses and corpora albicans
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ORIGINAL PAPER
Estimation of the fertility rates of Japanese wild boars (Sus scrofa leucomystax) using fetuses and corpora albicans Tomoka Tsuji & Mayumi Yokoyama & Makoto Asano & Masatsugu Suzuki
Received: 21 June 2012 / Accepted: 6 November 2012 / Published online: 4 December 2012 # Mammal Research Institute, Polish Academy of Sciences, Białowieża, Poland 2012
Abstract Effective population control of Japanese wild boar (Sus scrofa leucomystax) requires reliable information about population dynamics. Fertility rate is the fundamental component of reproduction to evaluate population dynamics. However, little is known regarding the fertility rate of Japanese wild boar. The traditional hunting practices make it difficult to obtain pregnant females and calculate the fertility rate by checking fetuses as is performed in other countries. Therefore, we focused on the corpora albicans (CA) as the CA remains in the ovaries of postpartum females after pregnancy. This study aimed to evaluate the utility of CA and estimate the fertility rate of Japanese wild boars using CA. Histological analysis of ovaries enabled us to discriminate type 1 CA, which remains for 1 year after breeding. Type 1 CA is a superior indicator compared with lactation in
the non-pregnancy season because it allows verification of postpartum females over a long period. The fertility rate was calculated by the combination of pregnant and postpartum females using fetuses and type 1 CA from April to November. The fertility rate of the females captured after the second pregnancy season was 90.3 % during the pregnancy period and 100 % during the non-pregnancy period. The high fertility rate of adult females suggests that intensive adult female harvesting is needed. Our new method to determine fertility rates contributes to developing a monitoring system to adequately control Japanese wild boar population. Keywords Fertility rate . Corpora albicans . Fetus . Non-pregnancy season . Japanese wild boar (Sus scrofa leucomystax)
Communicated by: Mabel D. Giménez T. Tsuji The United Graduate School of Veterinary Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan M. Yokoyama Wildlife Management Research Center, Hyogo, 940 Sawano, Aogaki-cho, Tanba, Hyogo 669-3842, Japan M. Asano (*) Faculty of Applied Biological Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan e-mail: [email protected] M. Suzuki Faculty of Applied Biological Sciences, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan M. Yokoyama Institute of Natural and Environment Science, University of Hyogo, Hyogo, Japan
Introduction Japanese wild boars (Sus scrofa leucomystax) have been an attractive game meat and an economic pest in western Japan since approximately the 1960s (Kanzaki and Ohtsuka-Ito 1997; Ohtsuka-Ito and Kanzaki 1998; Takehana and Kanzaki 2004). Few Japanese wild boar populations have spread due to excessive hunting and snow depth in eastern and northern Japan (Ministry of the Environment 2004). However, in the past few decades, the populations have drastically i
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