Upper and Lower Critical Temperatures – what are they?
Calves will aim to maintain their core body temperature between 10°C and 22°C. Either side of this range the calf will use energy to restore body temperature back to their target range which is known as the thermoneutral zone. The thresholds of the range are known as the upper and lower critical temperatures. When a calf reaches the upper or lower critical temperature, they will be diverting energy that could have been otherwise used for growth and immunity to increase or decrease their core temperature. The thermoneutral range will vary slightly depending on the age of the calf and will be affected by wind speeds and humidity. Above 25°C calves will be at risk of heat stress.
Top tips for managing calves in hot weather
Calves that are suffering from heat stress will be lethargic and have increased respiratory rates. They will also have a reduced milk and feed intake, affecting growth rates again. During times of abnormally warm weather there are several things you can do to help your calves through the heat.
Firstly, ensure you are monitoring what the temperature is at calf level. Consider getting a thermometer and monitoring around pens or if using hutches ensure you know what the temperature is reaching inside hutches. If hutches are sited on unshaded concrete, check if heat is reflecting off concrete yards. Consider providing shade to the pen outside the hutch to allow calves to shelter from the sun whilst maintaining maximum ventilation, or move hutches temporarily into an empty building. With different ventilation the temperature can vary in housing. Think about if you can improve ventilation without causing draughts.
It is also important to ensure the calves have access to plenty of water and that this is being changed frequently to ensure it is as cool as possible, try to keep the water out of direct sunlight. Consider reducing the stocking rate as high stocking rates will cause increase in temperature inside buildings and sheds and may make it difficult for calves to get access to water.
Shade should be provided so calves can escape the heat of direct sunlight. Any management plans such as vaccinating or fly treatment should be rearranged to reduce the chance of heat stress. If they are absolutely vital speak to your vet for further advise on how to manage on the day but plan to do any movement during the coolest parts of the day.
With the warm weather will also come flies which should be managed to prevent diseases such as New Forest Eye. Speak to your routine vet at your Herd Health Plan about the best way to manage flies on your farm either through spot on products, or consider use of friendly flies, parasitic wasps that aim to minimise the fly population on farm.
Ellen Taylor BVetMed MRCVS
