Electrolyte supplementation of export cattle and further investigations in the heat stress threshold of sheep and dairy cattle

Summary

This project involved three separate but linked experiments into the physiology of livestock heat stress. Experiments further investigated the supplementation of specific electrolytes in the water to cattle. In a summer feedlot, 30 animals received electrolytes over 18 days, and were compared with 30 unsupplemented animals. There was a live weight advantage of 2% after 12 days, during which time the supplemented cattle drank and ate more than the controls. This live weight difference was not sustained and the animals were not different at 18 days, nor after a further 7 days. A fluid balance experiment on six heifers held for seven days at high wet bulb temperatures in the climate controlled rooms did not produce any significant differences between supplemented and control groups. There was a significant increase in extracellular fluid volume in both groups after exposure to the heat. The heat stress thresholds for heavy rams, wethers, ram lambs and pregnant Friesian heifers were determined by logging core body temperature as they were exposed to increasing wet bulb temperatures over several days. The temperature at which they were 0.5°C above their normal core body temperatures was approximately 26°C wet bulb for the ram lambs, and 27°C wet bulb for the other classes of animals.