NWF’s head of Technical Adam Clay says the impact of higher temperatures coupled with humidity leads to cows, particularly under high metabolic pressure, to become highly stressed. Feeding and diet plays a key role in managing thermal stress and its effect on production.
“It is generally considered that an adult cow’s thermal neutral zone is between 5 and 20 degrees C, but once temperatures rise above this level, cows, particularly those under high metabolic pressure, can become highly stressed,” says Mr Clay.
“This, however, does not give any appreciation to the impact humidity can have, which means the occurrence of heat stress, or more accurately, thermal stress is far more common than we may think.
“A Temperature Humidity Index (THI) of 68 is now considered to be the point dairy cows become stressed and will show signs of thermal pressure, this can occur at 22 degrees C and from 45% humidity.”
Two key areas are affected:
– Dry matter intake is typically reduced by 10 – 30% due largely to a change in feeding patterns, but also due to the amount of heat produced by the rumen fermenting nutrients, particularly fibre.
– Energy requirements increase by up to 20% due to an increase in panting, blood flow and drooling since cows sweat very little.
“The result is likely to be in a drop in milk yield, milk fat and protein and eventually reduced signs of bulling and even conception rates. Dry cows are also high risk, particularly since they are on high forage diets so look out for reduced intakes and increases in retained cleansings and milk fever,” he said.
Management factors to help alleviate the thermal stress include:
– Ensure adequate provision of clean fresh water, an adult cow requires approximately 120 litres of water per day, but this can increase to over 150 litres with high yielding cows in higher temperatures, ensure at least 10% of cows can have easy access to water in one go
– Feed buffer feed late afternoon or evening once the temperature has reduced
– Buffer the rumen using rumen buffers and/or probiotics such as live yeasts. This is to help mitigate the effects of increased gorge feeding and reducing butterfats
“There are nutritional elements which can have a positive response, however, this positive response may be mitigating the negative effects of thermal stress,” said Mr Clay.
“Due to an increased energy requirement, increase energy density, ideally through the use of protected fat. Increased carbohydrates (starch and sugars) is also an option, however, this will put added pressure on an already stressed rumen environment,” he added.
Contact the NWF Agriculture team on 0800 756 2787 for feeding advice.
Written by Jennifer MacKenzie for The Journal, Holstein UK membership magazine published 5 Oct 2018.