Greater intensification of farming leads to more pressure on stock at certain times of the year. Heat stress in milking dairy cattle could be a threat on hot summer days.

With large scale irrigation systems removing shelter and shade from the environment, farmers need to be sure their stock are not suffering.

This research proves no negative responses occurred in the Canterbury areas surveyed, and it is hoped that lessons learnt here, could be applied to intensive dairying in the hotter climes of Central Otago or MacKenzie Basin. Many eyes will be watching.

Canterbury’s hot summer weather is not an impediment to dairy cow productivity, Associate Professor Graham Barrell,  who will present his findings to dairy scientists at an Australasian symposium at Lincoln University next week. The theme of the symposium is “Meeting the challenges of pasture-based dairying”.

His study suggests that reconsideration might be appropriate for  the local NZapplication of the commonly accepted international figure for predicting the onset of heat stress in dairy cattle  -  a Temperature Humidity Index (THI) value of 72. A three-part research project led by Associate Professor Barrell and  conducted on 13 dairy farms in the Selwyn District of Canterbury, including the Lincoln University Dairy Farm, and involving an analysis of Canterbury meteorological data for a recent five-year period, revealed that  -

Many sites in the region experienced at least three days per month in summer when the peak THI exceeded 72. While regular  changes in body temperature occurred throughout the day in dairy cattle, peaking in the afternoons, there was no evidence of cause and effect between THI and body temperature and until the former exceeded 72. Analysis of data from the Selwyn farms for two months of summer 2008-2009, when 19 days out of 90 had peak THI values exceeding 72, showed no evidence of a negative connection between the THI values and the amount of milk solids produced.
 

“The hot days in Canterbury during summer were not associated with a loss of milk production in dairy cows, even on occasions when the THI reached values in the high 70s. The fact that the cows on the farms in our study were able to maintain productivity on these occasions suggests that the heat load was never excessive.

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