Relationship between overfeeding and overconditioning in the dry period and the problems of high producing dairy cows during the postparturient period

In dairy cows, overfeeding during the dry period leads to overcondition at calving and to depression of appetite after calving. As a consequence, at c alving overconditioned high-producing dairy cows inevitably go into a more severe negative energy balance (NEB) postpartum than cows that have a norma l appetite. During the period of NEB, the energy requirements of the cow ar e satisfied by lipolysis and proteolysis. Lipolysis results in an increased concentration of non esterified fatty acids (NEFA) in the blood. In the li ver, these NEFA are predominantly esterified to triacylglycerols (TAG) that are secreted in very low density lipoproteins (VLDL), In early lactation i n cows with a severe NEB, the capacity of the liver to maintain the export of the TAG in the form of VLDL in balance with the hepatic TAG production i s not always adequate. As a result, the excess amount of TAG accumulates in the liver, leading to fatty infiltration of the liver (hepatic lipidosis o r fatty liver). The NEB and/or fatty liver postpartum are frequently associ ated with postparturient problems. In general, a severe NEB induces changes in biochemical, endocrinological, and metabolic pathways that are responsi ble for production, maintenance of health, and reproduction of the postpart urient dairy cow. These changes include a decrease in blood glucose and ins ulin concentrations, and an increase in blood NEFA concentrations. High NEF A concentrations caused by intensive lipolysis are accompanied by impairmen t of the immune system, making the cows more vulnerable to infections. Meta bolic diseases such as ketosis, milk fever, and displaced abomasum are rela ted to overcondition at calving. The changes in biochemical, endocrinologic al, and metabolic pathways are associated with delay of the first visible s igns of oestrus, an increase in the interval from calving to first ovulatio n, a decrease in conception rate, and a prolonged calving interval. It is p ossible that the increased blood NEFA concentration directly impairs ovaria n function.