Impacts of Metabolism and Nutrition During the Transition Period on Fertility of Dairy Cows

In early postpartum, high-producing dairy cows undergo a period of extensive tissue catabolism because of negative nutrient balance. Metabolic unbalances can lead to diseases, which are known to depress fertility in dairy cows. Negative nutrient balance has been associated with compromised immune and reproductive functions in dairy cows, and a compromised immune system leads to greater risk of diseases. Low circulating concentrations of glucose and insulin associated with elevated concentrations of non-esterified fatty acids (FA) and ketone bodies postpartum have detrimental effects on the oocyte, granulosa, and immune cells, disrupting their metabolism and reducing viability. Therefore, minimizing the extent and duration of negative nutrient balance in early lactation is expected to improve fertility. Reductions in circulating concentrations of Ca around parturition are also linked with impaired immune competence and have recently been linked with uterine diseases in dairy cows. Manipulation of the diet to influence metabolic health might benefit fertility. Dietary additives that influence rumen or intermediary metabolism to favor postpartum health, and supplementation with specific fatty acids during early lactation and the breeding period are potential alternatives to offset dietary insufficiencies and reestablish metabolic health in early lactation. INTRODUCTION Dairy cows must become pregnant and deliver a calf in order to undergo proper mammary development and lactogenesis. Reproduction is also critical to production because it determines when primiparous cows become multiparous leading to increments in milk yield, alters the average milk yield per day of lactation, affects the number of replacement animals available and the risk of culling, and influences the rate of genetic progress. It is well described that poor health during the transition period suppresses fertility in dairy cows. Perhaps the most debated aspect is the association between negative nutrient balance in early lactation and subsequent resumption of ovulatory cycles, and establishment and maintenance of pregnancy in high-producing dairy cows. During periods of negative energy balance (NEB), extensive lipolysis and products from fat metabolism seem to influence oocyte competence and subsequent embryo development. In addition, impaired metabolic health often leads to immunosuppression and the occurrence of diseases that further reduce fertility. Managing cows in the transition period in a proactive manner to minimize nutrient imbalances is mandatory for proper health, but it often benefits reproduction as well. The High Plains Dairy Conference does not support one product over another and any mention herein is meant as an example, not an endorsement. 2012 High Plains Dairy Conference 98 Amarillo, Texas CLINICAL AND SUBCLINICAL DISEASES REDUCE FERTILITY OF