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How to navigate heat stress in dairy cattle


It may feel like the cooler season is around the corner, but there is still plenty of time for temperature and humidity levels to impact herd performance. In addition to reducing milk yields by as much as 10–25%, heat stress can cause:

  • Increased mastitis levels.

  • Lameness issues.

  • Reduced butterfat.

  • Fertility issues.

Temperatures as low as 15°C, when humidity levels are high, can impact your herd’s performance, and we often see these temperatures carry through until the winter months.

Common signs to look out for:

  • Cows congregating in cooler parts of the shed.
  • Cows being less active but standing for longer.    
  • Open mouth breathing at a rate >70/minute.
  • As much as double the water intake.
  • Reduced dry matter intake.
  • Inconsistent manure. 

It's a particularly busy time of year with silaging, harvesting and preparing for winter to name a few. We are here to help beat the heat and proactively maintain profitable production.

10 simple nutritional-based steps:

  1. If at grass, ensure access to shade so cows can get out of direct sunlight. If housed, ensure adequate air movement and quality.
  1. Provide access to fresh, clean and cool water, with a minimum of 60 centimetres of trough space per cow and adequate water flows that meet the increased demands.
  1. Feed a high-quality forage to ensure the optimal fibre diet levels required for normal ruminal fermentation. If cows are out at grass, supply a fibrous buffer ration.
  1. Supplement close-up and early lactation diets with a live yeast rumen balancer such as Yea-Sacc®. This will keep rumen microbes steadily active, increasing rumen turnover and stimulating dry matter intake.
  1. Rather than feeding additional concentrate or starchy grains, which reduce ruminal pH, consider using supplement fats, such as whole oilseed, tallow or rumen-protected fats. 
  1. Increase the rate of minerals to balance those lost through sweating, respiration and increased urinary excretion. Potassium (1.5–1.6% of DM), sodium (0.4–0.60% of DM) and magnesium (0.3–0.4% of DM).
  1. Feed during the cooler part of the day when cows are more likely to eat. Clean feed bunks daily to keep feed fresh and minimise spoilage and heating.
  1. Prevent accelerated aerobic spoilage by maintaining a tight clamp face and remove a minimum of 15 centimetres each day to minimise secondary fermentation.
  1. Regularly analyse feed for heating and the presence of mycotoxins that breed more rapidly during hotter periods. Alltech® RAPIREAD™ gives rapid mycotoxin test results, in-depth analysis and real-time recommendations.
  1. For high-producing cows, feed high-quality protein supplements and balance amino acid content. Optigen® can replace some vegetable protein to optimise ruminal fermentation, allowing additional space for forage.