Heat stress identified as humpy back cause

Confining sheep movement to cooler hours in summer recommended to avoid humpy back


Sheep
Questions remain over why male sheep seem to be more susceptible than ewes to humpy back, with hormones and muscle mass both suggested as possible reasons for susceptibility to temperature-related issues.

Questions remain over why male sheep seem to be more susceptible than ewes to humpy back, with hormones and muscle mass both suggested as possible reasons for susceptibility to temperature-related issues.

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The humble potato bush, or wild tomato, has often had been suspected as the culprit causing humpy back in sheep, a syndrome that affects full-woolled sheep in summer, especially as the plant is generally found six to 10 weeks after good rain.

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The humble potato bush, or wild tomato, has often been suspected as the culprit causing humpy back in sheep, a syndrome that affects full-woolled sheep in summer, especially as the plant is generally found six to 10 weeks after good rain.

Biosecurity Queensland senior veterinarian, Binendra Pratep has turned that on its head, saying his research points towards humidity, coupled with heat, as the causative factor.

Speaking on a Leading Sheep webinar to an audience of 55, half of who said they’d had problems with the debilitating syndrome manifested by sheep, predominantly rams, but also wethers and ewes, Binendra described it as a “management disease” that could be worked around by careful timing of mustering.

“Heat has been a suspect for a long time, but we had been missing the humidity factor,” he said. “When you put that in, it explains a lot of things.”

The conditions sheep experience at times are a bit like clothes drying – in dry air moisture evaporates quickly but when it’s hot and humid, the air has no room to pick up moisture molecules from a sheep’s breath.

“I’ve observed sheep trying very hard to get rid of body heat through respiration, to the point of panting,” Binendra said, adding that heavy wool hindered the convection process.

In 2009, the syndrome that shows up in sheep lagging behind the mob when mustered, walking with a stilted gait and arched back, possibly leading to death, was found to have affected 70 to 100 properties in western Queensland each summer, shaving between $5000 and $50,000 off enterprise profits.

Binendra said sheep were worth twice the amount these days, meaning even more productivity was lost from the problem.

Responding to intense questioning, he said viruses such as Bluetongue and plant poisoning had been ruled out during studies conducted over a long time frame.

“Animals can be living with conditions, worm burdens for example, but when they’re put under stress, those complications will make the animal go down quicker,” he said.

“Succulent plants, such as oxolates, affect calcium levels and movements, and could cause kidney stones, but that’s not always associated with summer; that can happen anytime.”

Humpy back is seen more in Merino sheep than other breeds, which Binendra said was a combination of there being more of that breed than shedding sheep, and the husbandry needs of Merinos that meant in some situations they needed to be moved more often in hot weather.

“I would strongly suggest not working sheep when temperatures reach a certain level,” he said. “If you’ve got to bring them in, in January or February, do it gradually.”

Morning musters were preferable to afternoon ones, because sheep spent all day generating and absorbing heat, which would take a cool night to eliminate.

Ground temperatures also needed to be considered for animals like sheep that are closer to the ground.

While Binendra was not willing to specifiy a particular temperature above which sheep shouldn’t be moved, saying it depended on a number of variables, he told webinar participants it was a disease that was in their hands to manage.

Ilfracombe grazier explores water cooling

Ilfracombe grazier David Brooks, who said he’d had “a real doing” with humpy back this summer, has done a few experiments himself and come to the same conclusion as Biosecurity Queensland’s Binendra Pratep.

“I ruled out worms and pulpy kidney – I think we’re on the road to solving the problem now.”

He split a mob of sheep purchased from Broken Hill into two paddocks and found the problem was less in the one where sheep had access to a muddy creek they could stand in, and cool water to drink rather than hot bore water in a trough.

“I found I had problems with sheep in the paddock, not just after I started mustering them,” he said. “I think it’s worse too if your trough isn’t shaded.”

David has a plan to cool water coming from trough floats with hessian, much like water bags were used to keep water cool for drinking before insulated water bottles were commonplace.

Binendra said cooler water would do a lot of good, in the same way humans used a cool drink.

“I’d say humpy back is a huge problem, especially with the dollars we’re outlaying now, around $160 to $180 landed,” David said.

The story Heat stress identified as humpy back cause first appeared on Queensland Country Life.

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