Summer Management of Calves – Reducing Heat Stress

We know dairy cows can become heat-stressed at this time of year, especially during the warm, humid weather we’ve been having recently. But how often do we consider heat stress in calves?

Calves have a thermoneutral zone, which is the range of temperatures in which they can maintain their core temperature. Calves have an upper critical limit of 25°C, however, they will start to feel the effects of heat stress at 21°C.

When heat stressed, calves use their energy to try to stay as cool as possible, instead of using energy for growth and immune development. Some key signs of heat stress to look for in calves are sweating, increased respiration rate, panting, excessive drinking and spending less time lying down. It is important to recognise these signs because heat stress can cause dehydration, reduced dry matter intake (DMI), reduced growth, and increased risk of diarrhoea. Prevention is key, and some strategies to support calves when temperature and humidity rise are discussed below.

1. Housing and Ventilation

• Increasing air flow and exchange is very effective at supporting calves when it is hot, however, be sure the house does not become too draughty. In some situations, it may be viable to install mechanical ventilation, such as fans or tubes.
• The calf’s environment should always be clean and dry, with bedding changed regularly to support calves and prevent the establishment of fly populations.
• When rearing calves in hutches, it has been shown that elevating them on one side can decrease internal hutch temperature and increase ventilation in warm weather.

2. Nutrition

• When calves are heat-stressed, they will not feel like eating as much, so DMI will decrease. At the same time, energy for maintenance can increase by 20 to 30% as the calf tries to regulate its core temperature. Therefore, it’s important to promote intake as much as possible. Offer smaller, more frequent feeds (3 times per day) to help keep the starter fresh, clean and free from moisture. Remember, calves are very sensitive to smelly, damp starters. Also, if still feeding milk, feeding frequency could be increased to provide the calves with more energy to support growth, performance and body temperature regulation.
• Clean, fresh water should be available to calves at all times to reduce the risk of dehydration and maintain rumen development. In the warm weather, calves will drink more water than usual, so be sure water troughs are working well and kept clean. An oral rehydration solution such as Osmofit, will help replenish electrolytes, rehydrate calves and prevent them from becoming susceptible to further issues e.g. metabolic acidosis.

3. Management

• Keep stressful situations to a minimum by only handling calves e.g. vaccinating or dehorning, first thing in the morning or later at night when it is cooler.
• Ensure an appropriate fly control programme is in place. Flies cause calves to stress, so keep the environment and equipment clean and sanitised to minimise the risk of infection and disease.
• Offer calves a cool, shady place to lie during warm spells as this will help them regulate their temperature. Reducing stocking density in group housing can also be of benefit.
• Taking the simple steps mentioned above can minimise the effects of heat stress in calves and promote the use of energy for growth and development instead.

By implementing these straightforward yet effective measures, the impact of heat stress on calves can be minimized, allowing them to allocate energy towards growth and development.