Heat stress warning for autumn-born calves

Dairy farmers are being urged to review support for pregnant cows this summer, amid warnings that heat stress could affect the health and performance of autumn-born calves.

Animal health specialists say high temperatures during gestation can reduce calf immunity, lower birthweights and increase the risk of disease during the first weeks of life.

Nia Williams, technical livestock manager at Nettex, said farmers may not immediately link hot weather in summer with calf performance later in the year.

“Cows calving this autumn are at greater risk of producing calves with impaired immunity, which can increase susceptibility to diseases such as scours during the first weeks of life,” she said.

Heat stress can reduce feed intake, alter metabolic function and suppress immunity in cows.

It can also affect mammary gland development during the dry period, with potential consequences for milk production in the following lactation and calf performance after birth.

“Calves born to heat-stressed cows are often lighter at birth and can show reduced growth rates both before and after weaning,” Ms Williams said.

“That makes colostrum management absolutely critical.”

Farmers are being advised to prioritise shade, ventilation, clean water access, dry cow nutrition and rapid colostrum intake after calving.

Ms Williams said calves should receive colostrum quickly after birth, with passive transfer levels monitored during the first week of life.

“A blood test between 1-7 days of age can be a useful tool to assess how effectively antibodies from colostrum have been absorbed into the calf’s bloodstream,” she said.

Calves struggling to suckle or showing signs of low energy in the first few days may also need additional nutritional support alongside colostrum.

Freshly calved cows can also face reduced appetite, dehydration and electrolyte loss, particularly during hot weather.

“During calving, cows can lose close to 60 litres of water through blood and uterine fluids, along with significant electrolyte losses,” Ms Williams said.

She added that supporting cows immediately after calving with energy, calcium, vitamins and electrolytes can aid recovery, encourage intakes and support health and milk production during the post-calving period.