By Chloe Mitchell, ASAS/ASAP communications intern
Dr. Frank Dunshea of the University of Melbourne was invited to present
the Bentley Lecture at this year’s American Society of Animal Science (ASAS) Midwest Meeting in Des Moines, Iowa. The Bentley Lecture is an annual lecture established in honor of Dr. Orville Bentley, where an international guest speaker is invited to speak due to Bentley’s interest in international research collaboration.
Dunshea’s presentation was entitled “Dietary strategies to ameliorate the physiological effects of heat stress in livestock.” He spoke on his extensive research into the use of antioxidants vitamin E and selenium, as well as chromium, betaine, and grain treatments to alleviate heat stress in livestock including cattle, sheep and pigs.
When fed above required levels, dietary selenium and vitamin E may alleviate the effects of heat stress in sheep. Sheep fed a high selenium and high vitamin E diet had lower respiratory rate and rectal temperature compared to those animals fed low selenium and low vitamin E. Plasma reactive oxygen metabolites were also reduced. Under heat stress, blood pH was elevated and bicarbonate was reduced; however, these effects were reduced in animals fed the high selenium, high vitamin E diet.
Chromium treatment in pigs was shown to increase blood flow to the skin to allow heat loss. It also decreased respiratory rate and increased feed intake, improving average daily feed intake over the duration of the study. Plasma cortisol was decreased by 25% in pigs with the chromium treatment, with no effects on plasma glucose, insulin or NEFA.
Dietary betaine acts as an osmolyte, improving water retention in steers. It may be a successful carcass modifier in steers as it can influence lean-tissue deposition. In pigs, betaine has been shown to improve growth efficiency by reducing maintenance requirements and improving lean-tissue deposition. Betaine also has the effect of preventing a drop in milk yield in dairy cows, with one of Dunshea’s studies showing it had the effect of increasing both milk yield and milk component yield during late summer.
Finally, Dr. Dunshea presented findings from studies utilising different grain sources in ruminant diets. Rumen fermentation has a direct correlation with metabolic heat increment, meaning that the rate of fermentation in the rumen can increase the risk of heat stress. Feeding grains that are slowly fermentable can reduce this risk. A trial was conducted with sheep allocated to two treatment groups; a maize grain plus forage diet, and wheat grain plus forage diet. Rectal temperature, heart rate, respiratory rate and left and right flank skin temperature were all lower during heat stress in the sheep fed the maize diet, as maize ferments more slowly than wheat.
In October of 2014, Dr. Dunshea was honoured as a Fellow of the Australian Society of Animal Production.