Heat stress is a risk for dairy cows in summer. When a cow produces and absorbs more heat than she can get rid of by respiration, evaporation (sweating), and air flowing across her, they develop heat stress. Modern dairy cows are more productive and have a higher metabolic rate, which generates more heat. Some common summer feeds, such as bulky dry feeds with lower digestibility, can exacerbate heat stress because the required fermentation increases the animal's internal heat production.
Heat stress leads to:
- Lower feed intake
- Reduced milk production
- Increased Somatic Cell Count (SSC) and mastitis
- Reduced reproductive performance
- Increased incidences of lameness
- Increased risk of Sub-Acute Ruminal Acidosis (SARA).
Effective management starts with recognising when heat stress begins. A common identification method is the Temperature-Humidity Index (THI) which is calculated using the outside temperature and relative humidity.
The average mean annual humidity in New Zealand is between 70 and 80 percent. Dairy cows can experience light heat stress at temperatures as low as 22 degrees C. (1) Cows under mild heat stress can lose up to 0.24 kgMS / cow / day (2) equating to a loss of up to @2.44 / cow / day, based on a $10.15 / kgMS payout.
Be on the lookout for:
- Increased respiration rate and panting
- Decreased lying time
- Decreased rumination time
- Huddling around the water trough or in groups
- Reduced feed intake
By the time you observe the visible signs of heat stress, you will already be experiencing a loss of production, so prevention is important.
Practical cooling strategies keeps your cows healthy and the milk flowing. Small changes make a big difference as temperatures rise.
- Free access to clean, adequate drinking water.
- Access to shade. During the hottest part of the day, allow cows to graze paddocks with shaded areas and a short walk through the cowshed.
- Cool the holding area. Cool the concrete before cows arrive. Set up the sprinklers to drench the cows with water, i.e. large water droplets.
- Adjust your feeding strategy. Allow the cows to consume the best quality forage during cooler nights.
- Adjust their diet. Provide high-quality forages to compensate for reduced dry matter intake and incorporate bypass fats.
- Use feed additives to maintain rumen pH. Maintain a stable rumen environment by adding a buffer or live yeast product.
- Monitor the weather.
