THINK about the way your own body feels after spending a day outside in the heat. You’re most likely a little dehydrated, lethargic and have no appetite. Dairy cows are no different, says dairy veterinarian Dave Gilbert of Horizon Dairy Vets.
“Cows experiencing heat stress will often have a decline in dry matter consumption. In return, this has a negative impact on production. It’s not uncommon to see milk yield decline anywhere from 0.5-4 litres and for fertility rates to have a 5% drop,” says Dave..
“Heat stress can also cause multiple secondary issues such as ketosis, increased days open and even a decrease in colostrum quality.”
Through data analysed by the more than 16,000 head of dairy cows his practice services, it’s not just extreme heat events with temperatures in the 30s that puts stress on herds and starts to chip away at productivity.
“Heat stress is triggered by a blend of relative heat and relative humidity. Due to the high humidity levels we have in the UK, farms can start to run into heat stress issues when temperatures reach the low to mid-20s,” explained Dave Gilbert. “While conditions like this may only result in a 0.5-1 litre drop in milk production, that is a significant toll on output when spread over a three-month period.”
As higher temperatures reduce dry matter intake, they also push cows out of their comfort zone for body temperature regulation.
According to Dr Richard Kirkland, ruminant nutritionist for Volac Wilmar Feed Ingredients, this will increase maintenance requirements by up to 25% as the cow’s breathing rate and panting increase to help lose heat, therefore reducing the proportion of diet energy available for production.
A key factor in protecting herd productivity during periods of declining dry matter consumption is to increase energy density of the diet, explains Dr Kirkland. But this needs to be done carefully.
“Simply swapping lower-energy forage for highly-fermentable cereals will effectively increase energy density of the ration on paper, but these starchy supplements will lead to increased acid in the rumen, which is already under pressure to function adequately and effectively during heat stress conditions. This can lead to acidosis, which knock-on effects include lameness and reduced milk fat production,” warns Dr Kirkland.
Producers also need to keep an eye on fibre consumption. Lack of effective fibre paired with lower feed intakes will reduce rumination and saliva production – a key rumen buffer – which can lead to lower rumen pH (more acidic). In return, this increases the risk of acidosis and milk fat depression.
“Good quality, highly-digestible forage should be offered to the highest yielding cows under the most stress, while digestible fibre sources such as sugar beet pulp will help maintain production,” advised Dr Kirkland. “Poor quality forage should be avoided as it requires a lot more work by the animal to ferment in the rumen and to digest – generating greater internal heat production.”
Supplementing diets with energy-dense nutrients like rumen-protected fats is the most effective way to help meet energy requirements while not adding to the acid load in the rumen like starchy sources of energy. When compared to forage, a proven calcium salt fat supplement has three times the level of ME, making it a great forage ‘extender’ on farms. Fat is also considered a ’cool‘ ingredient, generating very little internal heat production during digestion and metabolism.
However, producers need to consider the most-appropriate type of fat supplement based on the fatty acid profile of the supplement to best meet farm targets, rather than just considering the direct energy element.
“Fats are highly energetic, but it is the fatty acid make-up of the fat that will determine how the animal responds to the additional energy supplied,” explains Dr Kirkland. “Traditional calcium salt supplements offer a source of rumen-protected oleic acid (C18:1) which helps improve body condition, development of eggs and embryos, and total diet fat digestibility. New research shows that calcium salts manufactured with larger granules offer greater rumen-protection than smaller granules, resulting in greater delivery of oleic acid to the small intestine and a more-effective product. So, this also needs to be taken into consideration.
On the other hand, the high-C16:0 (palmitic acid) supplements are effective at stimulating milk fat production and may be of interest under heat stress conditions where milk fat often declines. However, palmitic acid can cause partitioning of nutrients away from body fat resulting in lower body condition which may not be desirable. By understanding the impact these key fatty acids have on specific areas of performance, farmers can better target overall herd productivity.”
While outside humidity and temperature is uncontrollable, there are many environmental factors that are.
“One of the most common issues I see contributing to heat stress for housed cattle is poor building design. If a building is relying on the stack effect for ventilation but doesn’t have adequate air inlets and outlets, then air is going to become stagnant and humidity levels will increase,” Dave Gilbert asserted..
“Keep a close eye on cows to monitor this. If they are standing in a group in certain areas of the building, rather than laying down in their cubicles, then ventilation needs to be addressed as soon as possible.”
Since grouped cows will generate a lot of body heat, the 2005 Royal Vet College graduate advises that the collecting yard is not crowded. If that is unavoidable, fans should be installed to keep air moving and to keep cows from becoming overheated.
And most importantly, cows need to have free access to highly palatable water.
“There should be at least 10cm of water trough space per cow, so building stocking density should factor this in.
“On an average day, a lactating cow will drink 80-120 litres of water a day – which will go up significantly during hot periods. Failure to provide adequate drinking water will come with serious consequences to health and performance.”
Through a combination of managing controllable environmental factors such as ventilation and adjusting diets to meet energy requirements, dairy farms can significantly reduce the impact of heat stress.
“Adapting the diet isn’t a fix for poor housing conditions, just like having excellent housing conditions isn’t going to negate the need for diet changes,” affirmed Dr Kirkland. “Work with your vet and your nutritionist to find the best solutions for your herd to minimise the impact of heat and to protect long-term production.”