Galactopoiesis, Seasonal Effects

Abstract

Three management tools consistently increase milk yield in lactating dairy cows during established lactation: administrating exogenous bovine somatotropin (bST), increased milking frequency and increased photoperiod. Short day length during the dry period also increases milk yield postpartum while long day length during the dry period is associated with decreased milk yield in the next lactation. These management tools have separate mechanisms of action and are therefore additive in their impact on milk yield. Season of year affects both yield and composition of milk. Seasonal variables known to impact milk and composition yield are photoperiod and thermal environmental variables such as temperature, wind-speed, solar infrared load and humidity. Heat stress alters metabolism of lactating dairy cows and changes the hierarchy of peripheral tissue fuel selection. Milk composition is also markedly altered by nutritional management. This permits the opportunity to improve the nutritional value of milk by altering milk composition through dietary management.