ACT NOW TO BUILD HERD RESILIENCE TO HEAT STRESS

Focusing on feed management and cooling cows could help build herd resilience to heat stress and lower the chances of mastitis and lameness linked to endotoxins.

Heat stress is an ever-increasing problem for dairy cows, with heat events occurring earlier in the year and hitting new highs. This year, temperatures of 18C were achieved in March, with a high of 26C seen in London in April and the highest May temperature on record of 35.1C hit earlier this week. And that’s before the summer truly kicks into gear.

With heat stress occurring at temperatures as low as 18C, particularly if humidity is high, Peter van der Vegt, Volac’s lead for Technical Services says it’s vital preventative measures are put in place to protect yields and long-term cow health.

“A period of heat stress is often followed by a spike in lameness and mastitis a few months later, but it needn’t be the case,” he says.  “The key is to understand the cause of health and productivity issues caused by heat stress. This stems around preventing the production of endotoxins, which are largely to blame for health issues that occur after a heat event.”

Peter says a cow under heat stress will eat and ruminate less, which reduces saliva production. Panting also produces more carbon dioxide which further reduces her buffering capacity. She’s also more likely to binge eat when the environment cools. All this increases rumen acidosis risk. Acidosis leads to a decrease in the rumen pH causing rumen bacteria to die. Gram negative bacteria then release components of their outer cell walls, called lipopolysaccharides (LPS), which are endotoxins.

“Stress also causes gaps to open between the cells lining the rumen and hind gut, and this can cause an influx of LPS into the blood,” Peter explains. “LPS can settle in soft tissues like the hoof and teats resulting in lameness and mastitis. The immune system also fires-up to try and get rid of LPS, diverting energy away from milk production.”

This leaky gut also raises the risk of mycotoxins entering the blood. Mycotoxins are produced by certain moulds which grow on bought-in feeds and silage. 776 animal feed and forage samples were tested in the UK & Ireland in 2025 as part of Volac’s Mycocheck service, with 93.2% of those positive for one or more mycotoxin. These invisible toxins have wide-ranging effects including reduced feed efficiency, suboptimal fertility and lameness and mastitis due to their impact on the cow’s immune system.

Peter says it’s possible to reduce the impact of heat stress and protect the cow from endotoxin and mycotoxin challenges by optimising cow comfort and cooling cows.

“Ensure cows are provided with a consistent, well balanced, easily accessible ration to lower acidosis risk. That will be helped by providing plenty of feed space and pushing up regularly to optimise intakes. Also, speak to a nutritionist about adapting the diet in response to heat stress. This may mean raising the energy density by feeding a rumen-protected fat, such as Megalac. Cows low in energy balance will be more susceptible to endotoxins,” he says.

He also urges farmers to incorporate the mycotoxin remediator and endotoxin binder, UltraSorb R into the ration in advance of hot periods so cows are better able to cope.

UltraSorb R is exclusively available through Trident MicroNutri and contains specially selected minerals to bind various mycotoxins and endotoxins; plus biological active agents to transform and detoxify the harder to bind mycotoxins. Yeast components also help to support gut health.

Peter believes taking a preventative approach will benefit staff time and herd performance. “Cows in need of your attention take up most of your time, so ultimately if you can have less mastitis, less lameness, it will free up time to spend elsewhere managing the herd,” he says.