The Transition Period in Dairy Cattle, Physiology and Nutritional Consideration, an Overview

The 6-8 week period centered on parturition, known as the transition or periparturient period, is critical to welfare and profitability of individual cows. Fertility of high producing cows is compromised by difficult transitions. Deficiencies in either nutritional or non-nutritional management increase risk for periparturient metabolic disorders and infectious diseases, which decrease subsequent fertility. A primary factor impeding fertility is the extent of negative energy balance (NEB) early postpartum, which may inhibit timing of first ovulation, return to cyclicity, and oocyte quality. In particular, pronounced NEB during the first 10 days to 2 weeks (the time of greatest occurrence of health problems) is critical for later reproductive efficiency. Concentrations of insulin and insulin-like growth factor-1 (IGF-1) likely link energy (and nutrient) status and reproduction, and both are lower in cows with severe early lactation NEB. Concentrations of nonesterified fatty acids (NEFA) and β-hydroxybutyrate (BHB) increase in response to NEB, are useful indicators of metabolic status, may decrease dry matter intake (DMI) and may play a direct role in decreasing fertility. Suboptimal management of non-nutritional factors before and after calving (cow comfort, overcrowding, facility design and repair, heat relief) leads to stressors that may increase systemic inflammation and decrease DMI. Nutritional management before calving should aim to promote appetite and high DMI in the early post-calving period, which is the primary determinant of postpartum NEB. Avoiding over-conditioning and preventing cows from over-consuming energy relative to their requirements in late gestation result in higher DMI and less NEB after calving. A pooled statistical analysis of previous studies in our group showed that days to pregnancy are decreased (by 10 days) by controlling energy intake to near requirements of cows before calving compared with allowing cows to over-consume energy. To control energy intake, total mixed rations (TMR) must be well balanced for metabolizable protein, minerals and vitamins yet limit total DM consumed, and cows must uniformly consume the TMR without sorting. Dietary management to maintain blood calcium and rumen health around and after calving also are important. Opportunities may exist to further improve energy status in fresh cows. Recent research to manipulate the glucogenic to lipogenic balance and the essential fatty acid content of tissues are intriguing. High-producing cows that adapt successfully to lactation can have high reproductive efficiency, and nutritional management of the transition period both pre- and post-calving must facilitate that adaptation.