Ingestion et digestion chez les ruminants soumis à un stress de chaleur

Abstract

Heat stress generally leads to a decrease in voluntaryintake, in relation to thermoregulation, in order to allow a decrease in heat production, especially due to rumenfermentations. The decrease in intake may also be due to a low availability of forage on rangelands, as well as itslow nutritive value and sometimes to a lack of drinking water. When feed intake is very low, digestibility may decrease, for one same diet. In controlled conditions andfor a same intake, an increase in temperature increases diet digestibility by 0.2 point per degree Celsius. To prevent the negative effects of heat stress, especially on feed intake, ruminants modify their intake pattern by grazing during the night when the temperature is at its lowest, by increasing the number of meals and decreasing their length. They also modify feed preferences and thus the composition of their diet. In intensive systems, it is suggested to provide a shelter, to use water mist, to increase the energy concentration of the diet, to provide a source of fermentable nitrogen when this may limit forage digestion, and to increase the cation-anion balance ofthe diet.