AS THE climate debate heats up, Australia has emerged as a world leader when it comes to minimising heat stress in livestock.
The US and Canadian feedlot industries are implementing Australian research following the deaths of 5000 lotfed cattle in Nebraska during 2007.
Australia's most recent case of heat-related deaths was at a southern NSW feedlot in 2000, when 1255 cattle died.
Heat stress in cattle causes respiratory disease, poor performance and meat quality, and reduced feed intake.
It can also lead to severe intestinal damage, resulting in acidosis or grain poisoning.
This summer, lotfeeders and cattle breeders are being urged to take an active approach.
Queensland veterinarian Kevin Sullivan said producers should have a heat-load strategy in place that took into account the site, infrastructure, and feed and nutrition programs.
Dr Sullivan said cattle cooled their bodies by passing manure and urine and by transferring body heat to their surroundings.
Summer rainfall, followed by increased humidity, could trigger heat stress, he said.
"The lethal combination is several days of high temperatures and humidity, no cloud cover and low air-speed," he said.
"Manure in feed-yard pens turns to mud, and produces ammonia."
Dr Sullivan said most at risk were fat or sick cattle, black bos taurus cattle, recently transported cattle and cattle that were not acclimatised.
Heat-producing roughage and forage hay should be replaced by low heat-producing fats and oils.
"Feeding before the cooler time of the day may help, so digestion occurs during the cooler hours," Dr Sullivan said.
During heat waves, cattle needed to be checked every two hours for feed intake, behaviour and respiratory rates.
Heat-stressed cattle spent more time standing, crowding water troughs and bunching to seek shade from other cattle.
Then followed an open mouth and laboured breathing, excessive salivation, convulsions and death.
Dr Sullivan said most Australian feedlots generated data from on-site weather stations to calculate a heat-load index.
Feedlots were using solar shades, sprinklers and nutritional manipulation.
"Once temperatures reach over 35 degrees (celcius), the key is to maintain feed intake to reduce the risk of acidosis," Dr Sullivan said.
"Fats and oils can be increased to 2-6 per cent dry matter, molasses at 3-8 per cent, supplemented with potassium, vitamin A and E, and betaine."
Betaine maintained cell water balance and improved intestinal performance.
Cattle would drink 50 per cent more water during heat waves, so an extra trough space was needed, he said.
