Supporting Milk Production During Heat Stress

Heat Stress Starts with Feed Intake

When temperatures rise, one of the first things dairy farmers notice is a change in feed intake. Research shows that heat stress reduces both dry matter intake and milk yield, with cows’ feeding behaviour altered to help cope with higher temperatures.

Cows naturally spend less time eating and feeding often shifts to cooler parts of the day. While this helps them regulate body temperature, it can make maintaining production more challenging, particularly in high-yielding herds.

When cows are eating less, every kilogram of dry matter needs to deliver as much energy and nutritional value as possible. Cows need to get more from every mouthful, helping them to maintain milk production and performance even when temperatures climb.

Understanding how heat stress affects feeding behaviour is the first step towards building a ration that works with the cow, rather than against her.

Why Cows Eat Less

One of the first responses to heat stress is a drop in feed intake. Eating and digesting feed generates heat, so reducing intake helps limit additional heat load.

But it’s important to note that it’s just as much about how they eat as how much they eat. Intake becomes more uneven, with cows shifting feeding to cooler parts of the day and often consuming larger meals in shorter windows. This ‘slug feeding’ pattern can lead to inconsistent nutrient supply across the day and make ration balance harder to maintain. In more severe conditions, this reduction can become significant, with dry matter intake falling by 20–40%.

These changes in feeding behaviour can have knock-on effects throughout the digestive system. Larger meals consumed less frequently place greater demands on the rumen, while longer periods between feeds can make it harder to maintain consistent digestion. Heat stress not only influences how much cows eat, but also how effectively they utilise the feed they do consume.

Rumen Stability and Feeding Decisions

Changes in feeding behaviour under heat stress have a direct impact on rumen function. As cows spend less time ruminating, saliva production drops, reducing the rumen’s natural buffering capacity. At the same time, more uneven feeding patterns make it harder to maintain a stable digestive environment. Recent guidance highlights how reduced rumination and altered feeding behaviour under heat stress can disrupt rumen stability and digestion, limiting how effectively cows can utilise the feed they consume.

Maintaining consistent rumen function becomes increasingly important as feed intake patterns change. Fibre digestion can become less efficient, reducing the value cows are able to extract from the diet. When intake drops, a common response is to increase concentrates to push more energy into the ration. On paper, it makes sense. However, adding more rapidly fermentable starch can make maintaining rumen stability more difficult, generating additional acid, particularly when feeding patterns are already inconsistent.

Instead of improving performance, it often leads to greater inconsistency in digestion and intake. Cows may show reduced cud chewing, more variable manure, and signs of suboptimal rumen function.

Making Reduced Intakes Work Harder

Some nutrients follow a different path through the digestive system. For example, rumen-protected fats are energy sources designed to pass through the rumen intact and be digested later in the small intestine, delivering a significant energy boost without contributing to fermentation or additional heat production.

This is a huge benefit in hot conditions. Fats provide more than 2.5-times the energy of cereals while producing less heat during digestion and metabolism, making them an efficient way to increase the energy supply from the ration when feed intake is reduced.

For farmers, this means more energy and nutrients can be delivered in every kilogram of dry matter consumed. Rather than relying on cows to eat more feed, the focus shifts to helping them get more from the feed they already consume.

Putting it Into Practice

Applying this on farm comes down to how nutrition is delivered through the ration when cows are under pressure and making each kilogram of dry matter work harder.

Rumen-protected fats enable this without changing feeding behaviour or increasing reliance on concentrates. They can be incorporated into existing rations to increase the energy density of the diet without adding to the acid load in the rumen, particularly important when intake is fluctuating from day to day.

This method is especially useful in high-yielding cows, where even small drops in intake can quickly affect milk production. Providing more energy and nutrients in every mouthful helps support performance and maintain consistency through the tank, reducing the likelihood of knock-on effects later in the lactation.

Products like Megalac are designed to fit easily into this strategy, giving farmers a practical way to support milk production when feed intake is reduced, without disrupting the system already in place. Where milk fat has also taken a hit, then products like Mega-Fat 70 or Mega-Fat 88 will stimulate milk fat production also.

How to Keep Cows on Track Through Heat Stress

• Encourage dry matter intake by feeding during cooler periods
• Avoid over-reliance on rapidly fermentable starch sources like cereals
• Monitor rumination and manure consistency as early warning signs
• Use energy-dense rumen-protected fats that support rumen stability during periods of stress
• Work with a nutritionist to keep rations balanced and consistent

Small adjustments in how rations are managed can make a noticeable difference to how cows cope through periods of heat. Maximising energy density with feed ingredients that also support rumen function helps maintain performance when conditions are less predictable.

Could your ration benefit from helping cows get more from every mouthful during heat stress? Contact us today.

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