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Don’t underestimate the cost of heat stress

With heat stress costing UK herds up to £80 per day, isn’t it time we looked at this silent monster and consider what we can do to beat it?

In the UK, it is easy to dismiss the effects of heat stress due to the variable summer temperatures. However, it’s a combination of temperature and humidity that will affect cow performance, and is therefore very relevant for the UK.
In terms of milk yield alone, it is costing the average UK herd around £80 per day*, and with finances at the forefront of everyone's minds right now, dairy farmers need to be aware of these serious financial implications and what can be done to help combat the effects.

The impact of heat stress are numerous. Milk yield and feed intake reductions are relatively easy to monitor, but there are more subtle effects such as metabolic and hormonal changes which may affect fertility and rumen health. This makes calculating the true cost difficult, yet it is clear the overall financial impact is significant, even with our variable summers.
For a spring calving herd, the effects to on-farm profitability are the most pronounced with cows heading into peak lactation through the hot and humid summer months. Every dairy farmer also knows that a stressed cow is more prone to other symptoms. It’s a very delicate balance to manage a high yielding dairy cow, so it’s vital to use every tool you can to make her life comfortable, as that will result in maintained milk yield and a healthy animal.
The temperature-humidity index (THI) is universally referenced when studying the effects of heat stress; it takes into account air temperature combined with humidity. For example, temperature may be mild but humidity high, indicating cows will suffer. Most cities in the UK have an annual average humidity of between 70-90%, so as a general rule assume humidity is high.
The graph attached below also highlights the effects of heat stress on fertility as well as milk yield. Pregnancy rates significantly drop from 27% to 14% as the temperature humidity index increases from 69 to 76. That’s a big difference and, with a cost of up to £4/day/cow for a calving interval over 365, it’s yet another huge cost to the business that has to be factored into the implications of heat stress. If you are breeding the majority of your herd throughout the summer, the impact to your bottom line is even more severe.
(Insert graph - Temperature-Humidity Index – Holstein cows) 

“Heat stress really needs to be taken more seriously in the UK,” explains Dr. Alison Bond, Rumenco’s commercial nutritionist. “It’s so easy to ignore, but if the cost was invoiced to you on a monthly basis, I know every farmer would sit up and take action.

“It should be tackled from a two-pronged approach,” she explains. “Environment and nutrition are the areas that need to be considered, and where changes can often be made. Obviously there are fans and sprinklers, however, in reality the majority of UK herds are grazed throughout the warmest months of the year.

“So, although these options can be adopted, typically there is limited time the cows are indoors to benefit from them. Farmers should ensure that cows have easy access to water and shade. Cows that are comfortable will chew their cud more which helps buffer the rumen and encourage dry matter intakes.

“Adjustments can also be made to the diet and how it is fed,” adds Dr. Bond. “If you buffer feed, simple modifications to routine can be made such as pushing the feed up more often or increasing the frequency of feeding from once to twice a day. You can also install, as previously mentioned, fans or sprinklers in the feed areas.”
Dr. Bond also advises farmers to make sure they’re feeding fresh food. “Avoid secondary fermentation and molds in the TMR and stored feeds,” she adds. “Always be aware of how heat and humidity also affect feed quality. Offering a high quality forage will promote digestion and consumption. These are all quick and cheap ways to combat the stress on the cow at this time of year.

“If you are not already, an easy alternative way to provide additional energy is to add fat and reduce starch. This applies year round, but even more so, during summer. As appetites decrease in warm weather, you need feeds that stimulate the rumen microbial activity to improve feed utilisation.

“Products such as XP have been proven through various trials to increase feed efficiency during times of heat stress by over 6%, and increase fat corrected milk yield by 4.5%. XP is a pre-fermented yeast product, which helps stimulate the growth and activity of beneficial bugs in the rumen and gut,” she explains.

“When rumen microbial populations thrive, feed digestibility improves ensuring increased availability to the animal. This is exactly what is required during a heat stress situation, helping to promote rumen health, resulting in increased intakes and improved yield.

“Furthermore, as XP is a pre-fermented product, it is very stable and therefore suitable for addition to the TMR.

“A lot of research has been carried out on heat stress; a recently published report from the Animal Consortium, which studied cows in Scotland over a 21 year period, illustrated how, even as far north as Scotland, heat stress was experienced when using the temperature humidity index, resulting in a decrease in milk yield and quality.

“This highlights the fact that all dairy farmers need to be aware of the impact of heat stress, and make the necessary changes to maximise herd performance,” says Dr. Bond. “The effects are nationwide; it is not exclusive, as many assume, to the southern part of the UK, although it can be more concentrated in that area, depending on the summer.

“Finally, it is important to remember that the damage caused by heat stress is not just current but will continue throughout lactation. Farmers should therefore act immediately.

“We have several more months this season where heat stress could affect your herd, so assess your farm and your feeding system, and make changes to reduce the costs of heat stress,” she concludes.


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