Heat Stress Nutrition: Are You Feeding The Right Fatty Acids?

While many associate heat stress with extreme summer temperatures, the Temperature Humidity Index (THI) shows that cows can experience heat stress well before temperatures peak, particularly as humidity rises.

Research has shown that performance can begin to be affected at relatively modest THI values, with the risk increasing significantly as THI rises above 74. This highlights why heat stress is often a challenge long before temperatures appear extreme.

The recent spell of warm weather experienced across many parts of the UK would have pushed THI values into the 80s at certain times of the day, placing cows under significant heat stress despite temperatures that may not have seemed extreme on their own.

As heat stress develops, dry matter intake falls, maintenance requirements increase, and herd performance begins to suffer. Supplemental fat is often recommended as part of a heat stress feeding strategy because it provides a concentrated source of energy while generating less metabolic heat during digestion than starches or fibre.

Most nutritionists would agree with that approach. What receives far less attention is the fatty acid profile supplying that energy.

Heat Stress Is More Than An Intake Problem

Reduced dry matter intake is one of the most recognised consequences of heat stress. However, heat stress does more than reduce feed intake.

As cows divert energy towards cooling mechanisms, metabolism changes and maintenance requirements increase. Losses in milk yield and milk solids are often greater than intake reductions alone would predict. For fresh cows and high-yielding animals, maintaining production while protecting body condition becomes increasingly challenging.

Simply increasing dietary energy density is not always enough.

Why Fatty Acid Profile Matters

Many discussions around supplemental fat focus on energy density, fat percentage or inclusion rate. Yet cows do not respond to a fat percentage. They respond to the fatty acids being supplied.

Different fatty acids support different metabolic outcomes, meaning two fat supplements with similar energy values can deliver very different responses within the cow.

For fresh cows and high-yielding animals, the fatty acid profile becomes particularly important. Vegetable oil-based fat supplements rich in oleic acid (C18:1) have been associated with improved energy utilisation and can help support milk yield, milk solids and body condition at a time when cows are already under significant metabolic pressure.

Many traditional palm-based supplemental fats provide a fatty acid profile heavily weighted towards palmitic acid (C16:0). While palmitic acid has a recognised role in supporting butterfat production, heat stress presents a broader challenge than maintaining butterfat alone. Fresh cows and high-yielding animals need more than butterfat support.

An imbalance between palmitic acid (C16:0) and oleic acid (C18:1) can significantly reduce the benefits achieved in high-yielding fresh cows, where energy demands are greatest. The question should not simply be how much fat is being fed, but whether the fatty acid profile supplied matches the targeted outcome.

The UFAC Approach To Heat Stress Nutrition

For many years, fat supplements have been compared primarily on the basis of fat percentage, energy value, or product format. Yet cows do not respond to a fat percentage. They respond to the fatty acids being supplied.

At UFAC, our focus is on precision fatty acid nutrition. Rather than viewing all fat supplements as interchangeable, we focus on how individual fatty acids influence milk yield, milk solids, body condition and overall cow performance. Not all fat supplements deliver the same response.

During periods of heat stress, supplying energy remains important, but understanding the balance of fatty acids within that energy supply can be equally important, particularly for fresh cows and high-yielding animals, where maintaining performance becomes more challenging.

Heat stress nutrition should be about more than increasing dietary energy density. It should focus on supplying the right fatty acids to support the herd’s production objectives.

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