Physiological Adaptations in Transition Dairy Cows

Dairy cows undergo tremendous changes during the transition from late gestation to early lactation. The importance of this period in determining health, productivity, and profitability has been underscored by the intense interest in nutrition and management of dairy cows during the transition period over the last several years. The fundamental driver of the physiological changes is to ensure provision of adequate nutrients for the calf, both prenatally and postnatally. Dairy production has capitalized on this metabolic drive by selecting for higher and higher milk production. After parturition, nutrient demand is not able to be met through feed intake alone because the rate of dry matter intake (DMI) increase is slower than the rate of milk energy output. As a result, the magnitude of metabolic challenge faced by modern dairy cows is almost staggering. As demonstrated in Table 1, requirements for net energy of lactation (NEL) essentially double “overnight” as cows calve and commence lactation.