Nutritional considerations of poultry during heat stress

Abstract

The term "heat-stress" is often used to define the response of the bird to most warmer environments where a different abnormal physiological response is observed. There are likely to be two or three different degrees of heat stress where the birds'' response is different and where goals may change from consideration for production through to survival. In view of these different physiological situations any attempt at manipulation of nutrient-intake must be flexible and oriented towards the birds'' most immediate needs. Fasting of chicks and/or use of carbohydrate-free diets dramatically increases survival time under conditions of acute heat-stress; both these mechanisms are thought to induce a metabolic acidosis that helps maintain pH in situations of respiratory alkalosis. The so-called thermic effect of feed should not coincide with the period of highest ambient temperature, and last feed intake should occur at least 3-8 hr before maximum temperature is expected. Cooling of drinking water has also been shown to be beneficial during heat stress, where increased performance of laying hens occurs as a result of increased feed intake. Various mechanisms of dietary manipulation are discussed which could lead to improvement in performance of broilers and layers housed under heat-stress conditions.