With summer can come highly variable and unpredictable weather. This year has been no exception, and it is important to consider the effects of heat stress on all animals in your barn. Calves are highly susceptible to these effects, as they have an upper critical temperature of just 26⁰C (79⁰F). Past this temperature, maintenance requirements increase, meaning calves require more feed to meet these requirements before growth can be achieved. These effects on growth can affect age at first calving or age to market.

In extreme temperatures, requirements are believed to increase by 20-30% (Drackley 2011). This is largely because calves use energy to release energy, as they attempt to cool by panting or sweating.

Consider the following management tips to help your calves fight the summer heat:


Cool water (10-15⁰C) helps the calf fight heat while using less energy. However, dehydration can happen quickly. As Kathleen Shore from Grober Nutrition points out, “During periods of water loss, (e.g. scours or hot, humid weather) or water restriction, reductions in body fluid negatively impacts metabolism and feed intake. Even mild dehydration (1-5% loss of body weight from water loss), with symptoms not visible to the human eye, reduces metabolic efficiency and impairs ability to regulate body heat.”

In fact, a change from 20-30⁰C increases water intake by 1L/d, with much greater increases past 32⁰C (Calf Rearing Guide).

Water is needed as calves will sweat. Sweating and panting allows moisture to evaporate, which takes heat with it. Misting with sprayers can create the same effect; heat dissipates with water as it evaporates off the animal. However, in high humidity, the ability to cool by evaporation is limited due to the moisture already present in the air.

Water needs to be fed in addition to milk, and should be fed free-choice. Water intake encourages consumption of starter (Kertz 1984), which may combat decreased starter intakes often seen with heat stress. Maintaining starter intake should help the calf meet its requirements, and facilitate rumen development to allow a smooth transition to weaning. However, for bacteria to survive in the rumen and ferment starter to develop the rumen, they must live in a water environment. Water in milk bypasses the rumen via the esophageal groove, and so free water is crucial for the young calf. Without appropriate rumen development, especially when weaning in warm weather, calves are more prone to stall-out. For best success, consider the following tips for feeding water and grain:

  • Keep water out of direct sunlight and change regularly to minimize algae growth
  • Use different buckets for water and milk to avoid bacterial growth
  • Dump starter daily to avoid mould growth
  • Keep grain from falling into water

Housing & Ventilation

Open all doors and side curtains, and hutches as much as possible. Even prop up the back of the hutch 6-8” (eg. with a scrap tire) to facilitate air movement. Hutches and low ceilings can radiate high amounts of heat onto the calf, with temperatures in hutches often several degrees higher. To combat this, air movement above the calf is most important to increase evaporation and avoid drafts.

Bedding should be removed more frequently; if wet or soiled, it will retain heat. Sand is also better than straw or shavings at dissipating heat.

Immunity – Colostrum, and lots of it!

Heat stress itself can suppress a calf’s ability to fight disease. Calves born during times of heat stress may also require more colostrum due to the following:

  • Decreased absorption of antibodies from colostrum by the calf
  • Lower quantity and quality of colostrum produced by the dam

Getting calves off to the right start with high colostrum intakes of 4L in 30 minutes will help your calves combat the challenges of heat stress when first born, and as they continue to grow in challenging weather.
For scouring calves make sure to rehydrate with electrolytes, in addition to milk.

Management notes

To minimize any further stress, make sure that any changes are made gradually. Calves like consistency, and can be more prone to disease and decreased digestibility with sudden changes. Changes in environment, including the effects of transport, can require two weeks for adaptation by the calf (Arieli et al. 1995), resulting in increased maintenance requirements during that time.

Also, perform any processing or movement of calves early in the day, when heat stress is minimal – on you and the calf!

Heat stress can be difficult to identify without sudden changes in your calves. If you’re not sure if your calves are affected, look for the following signs:

  • increase in water consumption – *look at the amount of water in the bucket when you dump it*
  • lethargic, ‘lazy’ behavior
  • standing rather than lying
  • panting, sweating
  • increase in disease; monitor incidence of scours
  • reduced feed intake and/or growth

For any suspected cases, take the temperature of the calf (normal range: 38-39⁰C, or 100.5-102⁰F). It can quickly reveal how much heat stress may be affecting your calves!