Why do you need to act?
Calves are more sensitive to heat than adult cattle. Their thermoregulation systems are still developing and with a smaller body mass means that they heat up faster. While heat stress can occur in calves from air temperatures as low as 20°C,their upper critical limit is around 25°C. In humidity, this effect worsens – mild heat stress can occur at a temperature-humidity-index (THI) of 72, with moderate stress between THI 75-78 and severe stress at THI 80+. Poorly ventilated hutches or housing can push the effective THI even higher than ambient THI readings we commonly assess for our milkers at grass.
With forecasted high temperatures for the rest of the summer, provisions need to be made to ensure that calves have enough energy to regulate their own body temperature.
Under heat stress, calves:
- Lose more water through heavier breathing and sweating
- Eat and drink less, reducing energy intake
- Face a greater risk of electrolyte imbalance
A weakened calf is also more vulnerable to infections from external pathogens, which can lead to further health problems. To test for dehydration in calves, a simple skin tent test can be performed, as well as looking out for sunken eyes.
Mitigation - how to combat heat stress
So, how to combat.
1 - Keep Milk Feeding a Priority
Milk is the calf’s main energy source, so they must keep drinking milk. This energy is vital for thermoregulation and reduce the impacts of heat stress.
Healthy calves are usually eager to drink, so that first feeding of the day – before the heat sets in – so this is your chance to offer extra energy by increasing the amount of liquid feed. By providing these extra litres helps ensure they get what they need before the signs of heat stress impact the calf’s susceptibility to drink more liquid.
2 – Offer Electrolytes Midday
Between the morning and evening feeds, offer Osmofit mixed with 2 litres of water at 25-35°C
This next generation electrolyte solution:
- Provides a precisely balanced nutrient supply
- Has excellent palatability, encouraging voluntary intake
- Helps calves recover faster from heat stress
- Reduces the risk of secondary infections caused by weakened immunity
Always make sure calves also have access to fresh, clean water alongside electrolytes.
3 – Maintain Adequate PM feeding
The evening milk feed should still provide enough liquid feed to meet the calf’s overnight needs until the next morning.
Even in cooler conditions, multiple studies have shown that feeding more milk improves average daily gain (ADG), future milk production, fertility, and lifetime performance.
Why Feeding More Milk Works
By feeding more milk, you:
- Provide extra energy for growth and immune support.
- Maintain a balanced nutrient supply for optimal development.
- Help calves cope better with environmental stress
Extra Cooling tips:
- Provide shade and good airflow in calf housing
- Avoid moving or handling calves during the hottest part of the day
- Keep bedding dry – wet bedding holds heat
- Avoid overstocking as much as possible – aiming for 3m2 per calf
- If you are bringing in calves from market or from another farm, offer them Osmofit electrolye on arrival at new farm, then 2-3 hours later offer milk
