How to improve reproductive efficacy from now in Japan? Find out the factors of late lactation to predict postpartum reproductive diseases.

Reproductive efficiency and performance in dairy cattle has been declining over the last 20 years in Japan. Recently, this has resulted in serious problems in dairy herds. There have been changes in the animals themselves and in the animal's environment, e.g. the genetic potential for milk yield has improved, the herd size of dairy farms has been expanding, the housing system of dairy cattle has been changing from tie stall to free stall, and total mixed ratio (TMR) feeding systems have become widespread. It is not clear whether the animals have adapted adequately to these environmental changes. Up till now, reproductive management has been undertaken by monitoring animal performance and/or hormonal treatments, and this has resulted in acceptable reproductive performance. However, conception and pregnancy rates have continued to decline, and the calving to calving interval has continued to extend. Consequently, the average parity and the average age at culling in dairy cattle have been declining. The most common causes of culling in dairy cattle are reproductive disorders in Japan. Therefore, in future, prevention of reproductive disorders will be required for both reproductive efficiency and animal welfare. During late pregnancy and the transition from the pregnant, non-lactating state to the non-pregnant, lactating state, dramatic changes are occurring in the dam including an increase in the fetal-placental mass and calving. Thus, the demand for energy, protein and minerals by the conceptus increases, the space within the abdominal cavity and the rumen capacity decreases due to the increased volume of the conceptus, the local immunological relationship between the fetal and maternal placenta dramatically changes, and physiological homeostasis is activated to adapt to these changes. If cattle can't maintain homeostasis before calving, the incidence of reproductive diseases will be greatly increased. We have been examining reproductive, nutritional and immunological factors to predict the occurrence of reproductive disorders as early as possible and to develop strategies to prevent them. It is unlikely that all dairy farms in Japan will be able to improve reproductive performance with general advice, due to the wide variation in feeding systems and management in Japan. Therefore, specific advice needs to be tailored to each herd, based on management systems employed within each herd. We have proposed that it is important to identify common risk factors across herds, to use these factors as an index for disease control and reproductive management and finally to demonstrate the relationship between these factors and fundamental improvement of the reproductive efficiency. We propose this approach with the aim of providing a breakthrough in improving reproductive performance in dairy cattle in Japan. The focus of this review will be that such an approach is important for improvement of the reproductive efficiency in Japanese dairy cows.