Latent Infection with Leptospira Serovar Hardjo and Reproductive Performance in a Dairy Farm in Hokkaido, Japan

Abstract

Bovine leptospirosis is a serious issue that impedes productivity because it often results in abortions and stillbirths. Moreover, cows can be asymptomatic carriers of Leptospira serotype Hardjo (L. Hardjo). Recently, the high prevalence of L. Hardjo-seropositive cows has been reported in Japan. However, to the best of our knowledge, the influence of subclinical infection with L. Hardjo on dairy productivity in Japan has not been reported. Thus, we compared the reproductive performance between L. Hardjo-seropositive and -seronegative cows at a dairy farm in Hokkaido, Japan. Milking cows were divided into L. Hardjo-seropositive (n = 54) and -seronegative (n = 55) groups according to the presence or absence of antibody-specific to L. Hardjo in the milk. The conception rates per insemination at 125, 150, and 200 days postpartum were significantly lower in L. Hardjo-seropositive cows than in -seronegative ones (P＜0.05). The calving-to-conception interval tended to be longer in the seropositive cows (median: 127 days vs. 113 days, P = 0.06); furthermore, incidence of pregnancy loss (embryo death and abortion) tended to be higher in the seropositive cows (10% vs. 2%, P = 0.098). L. Hardjo has been found to cause latent infections in the reproductive organs, possibly impeding the normal development of the embryo and resulting in lower fertility. The study results revealed that subclinical infection with L. Hardjo in dairy cows is one of the potential factors decreasing dairy productivity in Japan.