Dietary changes to reduce heat stress losses in dairy cows
Having a plan in place to adjust rations as temperatures spike can offset production losses associated with heat stress this summer.
Volac ruminant nutritionist, Dr Richard Kirkland, said: “When temperatures reach 25°C, cows can really start to be impacted by heat, reducing their feed intake.”
Intake continues to decline as temperatures rise, with research data showing a 20 to 40% decrease in dry matter (DM) intake when temperatures hit 40°C.
The effects become more pronounced in high humidity and the temperature-humidity index is often used to indicate the degree of stress in dairy cattle.
Higher humidity will see more severe heat stress issues at lower temperatures. A reduction in DM intake results in a reduction in energy intake, resulting in less energy available for production.
And it can be made worse by an increase in maintenance requirements, increasing upwards of 25% as breathing rate and panting are elevated to help lose body heat.
Dr Kirkland said: “If not managed, cows will quickly fall into an energy deficit. Other functions including fertility and milk production are significantly reduced.
“Studies have reported conception rates falling as low as 10% during the hottest months of the year and milk yield falling by 35%.”
Increasing energy density
When it comes to mitigating the effects of heat stress, energy density delivered via a rumen-protected fat should be a key priority, according to Dr Kirkland.
He added: “Simply swapping lower-energy forage for highly fermentable cereals will effectively increase the energy density of the ration, on paper.
“But starchy supplements lead to increased acid in the rumen, which is already under pressure to function effectively in hot weather. This can lead to acidosis, causing lameness and reduced milk fat production.”
Supplementing diets with energy-dense nutrients like rumen-protected fats is the most effective way to meet energy requirements while not adding to the acid load.
When compared to cereals a proven calcium salt fat supplement like Megalac has around 2.5 times the concentration of energy. Fat is also considered a ‘cool’ ingredient, generating considerably less heat during digestion and metabolism compared to other feeds - something producers need to be aware of when choosing feed ingredients.
“Digestion of feed requires energy and the process also generates heat internally,” said Dr Kirkland. “Good quality, highly digestible forage should be offered to the highest yielding cows under the most stress, while digestible fibre sources will help maintain production without increasing rumen acid load.
“Poor quality forage should be avoided as it requires a lot more work by the animal to chew and digest - generating greater internal heat.”
Dietary changes to reduce heat stress losses in dairy cows
Farmers should also consider the most appropriate type of fat supplement, based on the fatty acid profile to best meet farm targets.
Selecting fatty acids to support milk contracts
Aside from being an energy-dense feed ingredient, the fatty acid make-up of the fat will determine which aspect of performance can be most influenced.
Dr Kirkland concluded: “Cows in early lactation and approaching their next breeding window benefit from a traditional calcium salt supplement offering a source of rumen-protected oleic acid (C18:1). This helps improve body condition, development of eggs and embryos and total diet fat digestibility.
“On the other hand, the high-C16:0, or palmitic acid, supplements are effective at stimulating milk fat production and may be of interest under hot conditions where milk fat often declines.
“However, palmitic acid can cause partitioning of nutrients away from body fat resulting in lower body condition.
“By understanding the impact these key fatty acids have on specific areas of performance, farmers can better target overall herd productivity while also meeting cow energy demands during hotter weather.”
