Trial data showing the effects of summer temperatures on cow fertility, that becomes obvious after the problem has occurred, should encourage dairy producers to take action early.
“Cows can stop cycling and fertility will suffer before the cow shows any signs of heat stress,” says Cargill’s ruminant technical manager Philip Ingram.
Estimates show that a swing in temperatures from 14⁰C to 22⁰C, at a relative humidity of 60%, can cause 20% of eligible cows in a year-round calving herd to slip a cycle, according to the Thuringian State Institute of Agriculture and the Institute of Animal Breeding and Genetics.
“Although UK temperatures are not typically extreme, we do see significant swings in temperature and humidity, even within one week,” says Dr Ingram. “They have a significant negative influence on fertility.”
Reviewing fresh-air flow, easy access to pushed up feed and, for both housed and grazing cattle, plenty of water availability and shaded areas will help cows to regulate their core body temperature.
“Amending the diet and including a cooling rumen buffer are also part of toolkit for keeping cows on track. For example, Equaliser CoolCow helps regulate core body temperature by hydrating the cow at the cellular level, due to the osmolyte, and by restoring the electrolyte balance,” he adds.
“It helps to cool them down and to maintain rumen function, so intakes don’t faulter. The aim is to keep cows comfortable and enable them to maintain their normal pattern of lying and eating so production and well-being is maintained throughout the summer.”
For dairy cattle, the classic threshold at which heat stress affects performance is often quoted to be a temperature-humidity index (THI) of 68, which, in the UK, would be 22⁰C. “We’re now aware that fertility can be affected at a THI of 57 which would typically be about 14⁰C in the UK with its typical 60% relative humidity.
“If temperatures increase above this, the effect on fertility would be far greater. Estimates are that at temperatures of 27⁰C, which is possible in the UK, the proportion of cows slipping a cycle could increase to 43%.”
Equaliser CoolCow is a powder additive that is added to the lactating-cow ration – the TMR or compound feed – at a rate of between 100g and 150g/head/day from May to the end of September, to ensure cover throughout the summer.