How do you adjust the feed ration during heat stress in cows?

Heat stress reduces feed intake in cows by up to 25% — discover which ration adjustments truly make a difference.

Adjusting the ration for heat stress in dairy cows starts with reducing the thermal load through feed: choose less fermentable carbohydrates, more rumen-protected fat, and a higher nutrient density to compensate for reduced feed intake. Heat stress affects dairy cattle at a temperature-humidity index (THI) above 68, which occurs more frequently during Belgian and Dutch summers than it used to. Below, we answer the most common questions about nutrition and heat stress in dairy cows.

Which nutrients are depleted most quickly during heat stress?

During heat stress, electrolytes — potassium, sodium, and magnesium — are depleted most rapidly because cows sweat and pant more. At the same time, blood levels of vitamin E and selenium drop due to increased oxidative stress, while the demand for methyl donors such as betaine rises as the body works harder to regulate cell temperature.

The osmotic balance within the cell comes under pressure as body temperature rises. Cells lose fluid and electrolytes faster than they can be replenished, especially when water intake does not fully compensate for losses through respiration and perspiration. This has direct consequences for muscle function, rumen activity, and milk production.

Oxidative stress is a second bottleneck. At higher body temperatures, cells produce more free radicals. The cow’s antioxidant reserves — including vitamin E, selenium, and betaine — are therefore consumed more quickly. A ration that does not account for this makes the cow more vulnerable to infections and reduces reproductive performance.

In addition, the demand for calcium increases during periods of heat stress, partly because feed intake declines and the availability of calcium through the ration decreases. Potassium deserves particular attention: a level of at least 1.5% of dry matter is recommended during warm periods.

How much does feed intake decline during heat stress in dairy cows?

During heat stress, feed intake in dairy cows drops by an average of 10 to 25 percent, depending on the severity and duration of the heat period. In extreme heat, with a THI above 80, dry matter intake can decline even further, directly leading to an energy deficit, weight loss, and reduced milk production.

The drop in feed intake is a deliberate physiological response: digesting feed generates heat, and the cow limits her intake to reduce the thermal load. This mechanism protects the cow in the short term, but creates a negative energy balance over the medium term that is difficult to compensate for.

Additionally, in hot weather cows tend to eat more frequently during the coolest parts of the day — typically early in the morning and late in the evening. Failing to align feeding times and feed availability with these windows means missing a key opportunity to maximize intake. Offering fresh feed during the cooler hours increases the likelihood that cows will actually eat more.

Which ration adjustments reduce heat stress the most?

The most effective ration changes during heat stress are increasing nutrient density, reducing fermentable carbohydrates, and adding rumen-protected fat. This allows the ration to compensate for lower feed intake without generating additional heat in the rumen.

Specific adjustments with proven effects:

Increase nutrient density by adding more rumen-protected fat. Fat provides energy with minimal heat production during digestion.
Limit rapidly fermentable carbohydrates such as corn or grain starch. Fermentation in the rumen generates heat that places extra strain on the cow.
Raise the potassium level to at least 1.5% of dry matter to compensate for electrolyte losses.
Ensure adequate sodium and magnesium through the ration or drinking water.
Add antioxidants such as vitamin E, selenium, and betaine to counteract the increased oxidative stress.
Increase protein density carefully: protein digestion also generates heat, so opt for rumen-protected protein with high intestinal digestibility.

Beyond the ration itself, the timing of feed delivery plays a major role. Spread the daily feed allocation across multiple feeding times and offer fresh feed during the coolest hours. Also make sure that drinking water is always available and remains appealing, because a cow that drinks more will also eat more.

What is the role of betaine in the ration during heat stress?

Betaine plays a key role during heat stress as an osmolyte: it protects cells against fluid loss by maintaining osmotic balance, allowing cells to function better under thermal stress. At the same time, betaine acts as a methyl donor, supporting liver function and energy metabolism at the moments when the cow is under the greatest pressure.

In ruminants, betaine is partly broken down in the rumen, but the active fractions that reach the small intestine still deliver measurable benefits. Research points to stimulation of microbial protein production in the rumen, a positive effect on fiber digestion, and a shift in the acetate-to-propionate ratio that contributes to more efficient energy utilization.

What sets betaine apart from other additives is its combination of functions. As an osmolyte, it reduces the cellular stress associated with high temperatures. As an antioxidant, it helps limit oxidative damage. And as a methyl donor, it supports the transmethylation cycle, which comes under extra strain during heat stress. Learn more about betaine and how it works on our product page.

In practical terms, betaine supplementation in dairy cattle leads to higher dry matter intake, better milk production, and less loss of body condition during warm periods. This makes it a valuable addition to any summer ration for high-producing dairy cows.

When should you adjust the ration in warm weather?

Adjusting the ration in warm weather is advisable as soon as the THI exceeds 68 for several hours per day. At that point, cows begin to show measurable signs of heat stress: increased respiratory rate, reduced feed intake, and declining milk production. Do not wait until production has already dropped — by then, the damage has already been partially done.

In practice, this means that in Belgium and the Netherlands you can start making preparations as early as May or June, especially when weather forecasts announce warm periods. Preventive action is far more effective than reactive adjustments after feed intake has already declined.

A good rule of thumb is to adjust the ration in phases:

Early spring: review the ration for nutrient density and electrolyte levels. Adjust the potassium supply if pasture access is not yet fully available.
When heat is forecast: increase the rumen-protected fat fraction, reduce fermentable carbohydrates, and add antioxidants to the ration or drinking water.
During a heat wave: spread the feed allocation across multiple times, offer fresh feed in the early morning and late evening, and monitor water intake daily.
After the heat: gradually restore energy balance and monitor body condition score to assess whether additional measures are needed.

What mistakes do farmers make when adjusting the summer ration?

The most common mistake when adjusting the summer ration is acting too late: farmers wait until milk production has noticeably declined, while the physiological stress began weeks earlier. Other frequent mistakes include underestimating electrolyte requirements, increasing protein levels without accounting for the additional heat production, and neglecting the water supply.

Below are the mistakes we encounter most often in practice:

Adjusting too late: heat stress begins at a THI of 68, long before cows show visible signs of suffering. Do not wait for a drop in production as a signal.
Adding more protein without selection: rumen-degradable protein increases heat production. Choose rumen-protected protein with high intestinal digestibility.
Overlooking electrolytes: potassium, sodium, and magnesium are quickly depleted in the heat. Many rations fail to meet the increased summer requirements.
Underestimating water intake: a cow can drink up to 150 liters per day in the heat. Insufficient drinking points or lukewarm water significantly reduce intake.
Not aligning the ration with feeding times: if feed is only available during the day, cows miss the cooler window in the early morning and late evening.
Forgetting antioxidants: oxidative stress increases sharply in the heat. Vitamin E, selenium, and betaine are overlooked more often than the macronutrients.

A good summer ration requires proactive thinking and regular fine-tuning. Farmers who monitor the THI daily and adjust their ration accordingly will prevent the worst production losses and protect the condition of their cows throughout the entire summer period.

How Jodoco helps with heat stress in dairy cows

At Jodoco, we specialize in natural solutions that help dairy cattle better cope with the physiological challenges of heat stress. Our approach combines scientifically supported ingredients in formulas specifically designed to address the bottlenecks discussed in this article.

What we offer for dairy cattle in summer:

Acibet G: a liquid source of betaine, glycerol, isomaltulose, and organic acids that supports liver function, reduces negative energy balance, and stimulates feed intake. Trial results show that cows receiving 300 g of Acibet G per day maintain their milk production using 25% less concentrate per 100 kg of milk.
Acibet TMR: prevents TMR from heating up, keeps feed fresher and more palatable for longer, and thereby improves feed intake during warm days.
Betaine as an osmolyte and methyl donor: our natural betaine supports cellular hydration, reduces oxidative stress, and stimulates microbial protein production in the rumen — precisely the functions that come under the greatest pressure during heat stress.

Want to know which approach best suits your farm situation? Contact us and we will be happy to work with you on a practical, scientifically grounded summer ration plan for your dairy herd.