Ioannis Xypoleas, Animal Nutritionist MSc
Heat stress in milking cows occurs when the temperature-humidity index (THI) exceeds 68, which can happen even at temperatures as low as 22–25°C with high humidity (Fig. 1).
Effects of Heat Stress on Dairy Cows
Heat stress can significantly impact cow performance, leading to:
Reduced feed intake and milk production
Lower fertility rates and compromised overall health
Decreased milk quality and increased cases of mastitis
Higher incidence of metabolic diseases
Proper nutritional strategies can help mitigate these negative effects. Here are key approaches:
1. Adjust Energy and Nutrient Density
Increase energy density by adding bypass fats instead of increasing fermentable carbohydrates to reduce heat production from rumen digestion.
Use highly digestible fiber sources to maintain rumen function without excessive heat production.
2. Optimize Protein Supply
Provide high-quality, rumen-protected proteins (bypass protein sources) to maintain milk production.
Avoid excess dietary protein, as it increases metabolic heat due to nitrogen excretion.
Add rumen-protected amino acids to improve milk production, protein efficiency, and overall cow performance, especially during heat stress or high-production periods.
3. Maintain Mineral Balance
Supplement potassium (K), sodium (Na), and magnesium (Mg) to compensate for losses through sweat and maintain water balance.
Use bicarbonates or other buffers (e.g., sodium bicarbonate, potassium carbonate, magnesium oxide) to prevent rumen acidosis, which is more common in heat-stressed cows.
4. Increase Water Availability
Provide cool, clean water at multiple locations with increased flow rates.
Ensure at least 15 cm of linear trough space per cow to promote adequate hydration.
5. Feed Additives to Reduce Heat Stress
Yeast and essential oils – Improve rumen fermentation and fiber digestibility.
Betaine – Acts as an osmoregulator and helps maintain cellular hydration.
Niacin – May aid in reducing heat stress effects by improving blood flow and thermoregulation.
6. Adjust Feeding Management
Feed cows during the cooler parts of the day (early morning and late evening).
Increase feeding frequency to encourage intake.
Push feed frequently to ensure constant access in the feed bunk.
Reduce sorting behavior by providing a well-mixed total mixed ration (TMR).
Conclusion
Implementing these nutritional strategies can help cows cope with the challenges of heat stress during hot seasons. Taking preventive measures before heat stress begins leads to better performance and improved overall herd health.
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