SPECIAL REPORT
Cows energised on winter diets Lincoln University Agricultural Science graduate George Letham’s study into dairy cows feeding on high energy crops has earned him a leading graduate award. Anne Lee reports.
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ows wintering on high energy winter forage crops are unlikely to suffer from cold stress with new research showing that as long as they’re getting a full intake, temperatures could drop as low as -20.4 deg C before they would even start to shiver. Lincoln University Agricultural Science degree honours graduate George Letham has recently been awarded the 2020 NZ Institute of Agricultural and Horticultural Science (NZIAHS) Leading Graduate Award for Lincoln University. The award recognises his honours study which looked into heat production from cows fed six common wintering diets. The modelled heat production information was then used to find the lower critical temperature (LCT) based on two internationally accepted approaches which ultimately allowed for the development of an index for LCT’s and heat production representing most of New Zealand wintering systems. It’s the first time LCT’s have been modelled for NZ’s outdoor grazing, winter forage crop systems. “An LCT is the lowest temperature a cow can be in before it has to start using energy to stay warm.” George explains that once large ruminants such as dairy cows have eaten enough to meet their energy demands for maintenance and pregnancy the excess energy is used for weight gain and dissipated as heat. In cold temperatures the heat is retained to maintain the animal’s required body temperature. “A lot of the work done previously was done 30 years ago and was done internationally – there’s never been a study looking at animal welfare and cold stress in a New Zealand context or our wintering context.” George’s extensive modelling found that the higher the energy of the diet the greater it’s cold tolerance. 68
FODDER BEET PRODUCES HEAT Fodder beet for instance produced unexpectedly high heat production and corresponding tolerance to very low temperatures. A high intake fodder beet resulted in the highest heat production figure for the study of 83.2megajoules (MJ)/day. “Most people don’t have a reference for that kind of heat production but it’s equivalent to wrapping a cow in a household double bed 60-Watt electric blanket on its highest setting for 16 hours and 40 minutes. “The lowest heat production of 33.8 MJ/day was the equivalent of six hours and 30 minutes in the same kind of electric blanket. “It’s very unlikely cows wintering on high energy winter forage diets will ever reach their
Above: Lincoln University Agricultural Science students Alexander Koops (left) and George Letham.
Dairy Exporter | www.nzfarmlife.co.nz | August 2021
