IMPORTANCE OF IMMUNE FUNCTION FOR OPTIMAL REPRODUCTION OF DAIRYCOWS

摘要

One of the most widely-discussed issues regarding reproductive management of dairy cows is the historic decline in fertility for lactating cows that began about 1960. It is important to recognize that this situation is being reversed and there has been a steady increase in reproductive function in the last several years (Figure 1). Genetically, the dairy cow is still less fertile than the cow of 50 years ago: the predicted transmitting ability (PTA) of a Holstein bull for daughter pregnancy rate (DPR) in 1965 was +7.1 vs a PTA of +1.4 in 2015. Nonetheless, genetic merit for fertility has been increasing: the nadir for bull PTA for DPR (-1.1) in Holsteins was experienced in 2002. The improvement in genetic merit has involved increased emphasis on health and reproduction traits in leading selection indices like net merit. Fertility has also improved in recent years because of the incorporation of timed artificial insemination (Al) programs in reproductive management systems. Initially, these programswere designed to avoid problems inherent in estrus detection. Now, however, refinements in timed Al programs to optimize the endocrine environment of the cow mean that fertility to timed Al can exceed that following Al at detected estrus (Santos et al., 2017).