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Heat Stress in Calves

In warm or bright conditions, when there is heat and light intensity, calves are at risk of heat stress. During these periods, energy is used to lose heat from the body by sweating and increasing respiratory rate.


When and at what temperatures do calves start to get impacted?
Although calves have an upper critical limit of 25⁰C, they can start to feel the effects of heat stress at 21⁰C. Above 20⁰C the calf will have to use additional energy (roughly 20-30%) to maintain a normal body temperature, thus shifting energy away from growth and the immune system. Similarly, when it is cold, and calves require more energy to keep warm. When it is hot, calves require energy to keep cool.
Prolonged exposure to temperatures above 20⁰C can lead to a significant drop in daily live weight gain if not managed carefully. A calf suffering from heat stress is likely to reduce their starter feed intake, we know they require more energy to keep themselves cool and so it is essential the volume of milk replacer is not decreased. In fact, feeding more milk or milk replacer during hot weather will help to bridge the energy gap required to maintain growth rates and support the immune system.

Top tips for managing heat stress
• Monitor temperature in the shed daily – use a min/max thermometer and record temperature fluctuations.
• Provide clean, fresh water and plenty of it.
• Reduce sun exposure and improve airflow.
• Offer electrolytes when hot temperatures persist or as soon as calves show signs of mild dehydration.
• Where possible reduce stocking rates.
• Ensure any handling or routine work is carried out in the coolest part of the day.
• Do not drop or remove milk; consider increasing milk by 0.5-1L.


Nutritionally:
• WATER: Assess to clean, fresh water at all times is vital during warm weather to allow the calf the chance to cool down. Heat is transported out of the body during urination, the more water the calf can drink the better they can manage their temperature. Extra care needs to be taken to ensure beds remain dry and clean, wet warm environments will encourage pathogens to multiply.
• STARTER: A calf suffering from heat stress is much more likely to have reduced starter feed intakes. Ensuring feed is fresh can help promote intakes. This also highlights the importance of milk or milk replacer to bridge this gap.
• CALF MILK REPLACER: CMR volume should not be decreased as calves will need more energy for thermoregulation. Consider increasing milk by 0.5-1L.

For more information on preventing and managing the effects of Heat Stress in calves, speak to your local JPA Sales Specialist.

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