Heat stress management of Merino sheep: Responses to drinking water temperature and a yeast-based feed additive

Abstract

Conditions in the hot room in the climate-controlled housing used in this study were intended to simulate those experienced by Australian sheep in the post-discharge phase of the live export trade to the Middle East, i.e. 40°C and 60 % relative humidity between 0900 hand 1800 h and 30°C over night. Hot climatic conditions can lower an animal's production by altering physiological characteristics (body temperature, respiration rate, packed cell volume), behaviour (feed and water intake) and thereby affect feed digestibility, total excreta output and live-weight gain. The use of a yeast-based feed additive reputed to reduce the effects of heat stress was investigated in 16 Merino sheep in Expt. 1. A 2 x 2 factorial design was used with 1 group of 8 sheep in a hot room and the other group in a cool room; 4 sheep in each room were offered lucerne pellets containing the yeast-based feed additive and the other 4 were offered only lucerne pellets. Outer body temperatures (wool, skin and ear) and also mean respiration rates were higher (P<0.05) for sheep in the hot room than those in the cool room. Dry matter intake of sheep was higher (P<0.05) in the cool room but only during the hottest hours (0900 to 1700 h). Water intake and urine production were higher (P<0.05) in the hot room whereas feed intake and faecal output tended (P=0.07) to be higher in the cool room. The use of the yeast-based feed additive was beneficial, increasing growth rate of sheep (P<0.05). Respiration rate and other measurements were not influenced (P>O.05) by the use of the yeast-based feed additive. In Expt. 2, the effects of providing drinking water at different temperatures was studied in Merino sheep offered lucerne chaff ad libitum in hot or cool conditions.