Rutherglen shade experiment results
Lambs at pasture are able to effectively maintain their core body temperature by panting, without the need for shade.
Providing shade or an antioxidant feed supplement does not alter growth rates. These are the results of the Rutherglen shade experiment conducted in the summer of 2017, which support the concept that sheep are well adapted to our hot Australian summers.
This experiment was conducted on store lambs (body condition score 2.1 at the beginning, and 3.0 at the end) at pasture, with a modest growth rate of around 120 to 140 g/hd/day. If the lambs had been fed on feedlot rations for high growth rate, the results may have been different, but that wasn't tested in this experiment.
Sheep pant to assist with cooling, just as people sweat. It is vital that core body temperature remains in the isothermal range to keep the body functioning optimally. Lambs provided with shade panted less (around 60 breaths per minute) than those with no shade (90 breaths per minute) — but this natural compensation method was enough to maintain core body temperatures at 39.5 °C, as measured with core body temperature loggers.
The lambs were fed a supplement containing the antioxidants vitamin A and selenium, to test the hypothesis that this supplement would correct any oxidative stress the animals may have been experiencing as a result of the heat challenge. This supplementation didn't make any difference to the measured parameters. The lambs without shade panted the same amount, whether or not they were supplemented.
The lambs were also fitted with proximity loggers to see how much time they spent near the water troughs or in the shade (if provided to their group) — those results are yet to be analysed.
This research is providing valuable evidence on the shade requirements of sheep and once further analysis is completed could form the basis for on-farm management practices.