Protecting calves from heat stress

Calves are highly susceptible to the effects of heat stress when temperatures reach 26⁰C. Heat stress causes the calf to use energy to dissipate excess heat from its body, resulting in lower weight gain, compromised health, and difficulty achieving growth targets for age at first calving or age to market. Heat stress can also lower blood serum immunoglobulin levels, leading to a greater risk of disease and death.

Heat stressed calves can be difficult to identify without sudden changes. Monitor calves twice daily (at minimum), and look for an increase in water consumption, reduced feed intake or growth, lethargy, standing when they’re normally lying, higher respiratory rates, panting and/or sweating, and increased disease.

Producers should be cognizant of heat stress of calves in hutches. In the summer months, temperatures inside hutches can become very high, and calves do not have the freedom to move away. Consider moving hutches to a shady area during the summer months. Bedding should also be removed more frequently; if wet and dirty, it will retain heat. Sand is better than straw or shavings at dissipating heat, but all bedding must be clean, dry and comfortable.

Low ceilings in barns mimic heat experienced in hutches; opening windows and curtains, and adding fans or adjusting ventilation systems for summer air exchange rates will all help circulate air, while being mindful of drafts. Misting with sprayers can create the same effect as panting and sweating; 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.

Fresh, clean water should be offered free-choice alongside milk feedings. Monitor consumption and offer more if needed; a temperature change from 20 to 30⁰C increases water intake by one litre daily, with much greater increases past 32⁰C.

Dehydration can still happen quickly. During periods of water loss, (e.g. scours, hot, humid weather) or water restriction, reductions in body fluid negatively impacts metabolism and feed intake. Even mild dehydration reduces metabolic efficiency and impairs the calf’s ability to regulate body heat. For scouring calves make sure to rehydrate with electrolytes, in addition to milk feedings.

Maintaining starter intake can help the calf meet its energy requirements and facilitate rumen development to allow a smooth transition to weaning. Without appropriate rumen development, especially when weaning in warm weather, calves more easily succumb to the post-weaning slump.

Heat stress can further suppress the calf’s ability to fight disease. Calves born during times of heat stress may also require more colostrum due to lower quantity and quality produced by the dam and reduced absorption of antibodies by the calf.

To minimize any further stress, avoid performing any procedures or movements that may stress calves during the heat of the day and make sure that any changes are made gradually. Calves like consistency, and can be more prone to disease and reduced digestibility with sudden changes. Changes in environment, including the effects of transport, can require two weeks for adaptation by the calf, resulting in increased maintenance requirements during that time.