干旱区生态环境知识资源中心

Generally heat stress results from high temperatures and low hygrometry in arid and dry climates. During heat stress feed intake falls due to: thermoregulation that tends to decrease heat production from rumen fermentations; a limited availability of vegetation on rangelands or pasture; a decreased dietary value of ingested vegetal fractions; and a low availability of water.

In conditions of heat stress, the diet digestibility tends to increase, due to the decrease of feed or water intake levels which increases the duration of ingesta transit. But results under feeding conditions have shown an explicit relationship between the level of intake and digestion. When the level of intake is very low (-50% maintenance), digestibility can decrease. Underfeeding results in a reduction in the rate of volatile fatty acids absorption in rumen mucosa. In controlled conditions, the single effect of an increase of ambient temperature tends to improve the diet digestibility (0.2 point per C degrees Celsius) at the same level of intake.

To fight against the bad effects of heat stress on level of intake, ruminants can modify their feeding behaviour by grazing during fresh periods (frequently at night), increasing the number of meals and reducing meal duration. The animal can also modify ingesta choices and composition.

In the case of intensive conditions, it can be interesting to use shelters on pasture, provide water for animals, increase the energy density of diets, use a fermentable nitrogen sources when one of the limiting factors of digestion is the N degradability of diets, increase cation-anion balance and also adapt the animal management on rangelands to increase the level of intake.