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.
Calves have an upper critical limit of 25 °C but can start to feel the effects of heat stress at 21 °C. Above 20 °C, the calf will use additional energy to maintain normal body temperature, this shifts energy away from growth and the immune system. 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.
Heat stress in calves needs to be carefully managed, access 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.
Any handling or routine work that needs to be done like weighing, worming or vaccinating should be done early in the morning whilst temperatures are at their lowest to minimise the effects of heat stress.
Ventilation within calf housing can help with managing heat stress. Airflow and air movement helps keep calves cool, for sheds with poor ventilation where it is impractical to change shed design adding fans to pull fresh air through the shed can help. The fans should be used to move the air above the calves, to remove stale air, not to create a draft at ground level. Reducing stocking density within sheds or igloo is another element that can help mitigate heat stress; the more space a calf has away from others the easier it will be for them to regulate their body temperature.
A big risk for calves suffering from heat stress is dehydration; calves need to be closely monitored for the early signs of dehydration which require rapid action. Once a calf is dehydrated they are unlikely to finish their milk feeds and cannot drink enough water to rehydrate on their own, electrolytes must be provided. When temperatures remain high and calves could be at risk it may be beneficial to offer calves an electrolyte feed in the middle of the day, between milk feedings, as a preventative.
If left unmanaged a prolonged exposure to high temperatures can lead to a significant drop in daily live weight gain, an elevation in calf disease incidences and in severe cases death. For more information or to receive an electrolyte protocol contact a member of the NWF Youngstock team.
By Emily Jones, NWF Youngstock Specialist. Call Emily on 07936 367624 for youngstock advice or to book a farm visit.