Calves born in summer and fall experience significantly lower average daily gains than calves born other times of the year, according to a Pennsylvania study using a variety of housing types.1 A study in Ohio showed that for every 10-degree increase in air temperature above 77˚F, calf average daily gain (ADG) decreased by 5 percent. In addition, every 1-degree increase in a calf’s body temperature reduced ADG and structural growth by almost 15 percent.2
Calves can begin to suffer heat stress once the temperature in their environment reaches about 77˚F or 78˚F.2 But, other factors also come into play, including relative humidity, air flow, hair coat, bedding surface and whether the animal is exposed to sunlight versus shade. The preweaned life stage for calves offers just a small window of time to help them achieve their full lifetime potential.
I suggest minimizing the impact of heat stress on preweaned calves by focusing on:
- Milk feeding — Calves expend additional energy to stay cool, so every calorie counts. Feed calves enough pasteurized whole milk or mixed milk replacer and water at each feeding to provide enough calories and protein for growth. Also, be sure to increase the volume of whole milk or mixed milk replacer being fed in order to compensate for the additional energy expended to keep cool and accommodate for calf size. You wouldn’t feed a month-old calf the same amount as a week-old calf.
- Water — Provide 24-hour access to fresh, clean, cool water starting at birth. In hot weather, if calves are running out of water during the day, you need to regularly replenish the water supply between feedings. You need to give them ample opportunity to hydrate. Whole milk and conventional milk replacer should be balanced. Accelerated milk replacer diets have a higher concentration of solids, so access to free choice water is important for calves consuming this type of diet. Water also drives starter intake.
- Starter grain — Calves under heat stress often eat less starter grain. Promote starter intake by keeping grain supplies fresh. Be sure ample grain supplies are available in the evening, when calves are more likely to consume it.
- Shade — Allow calves to move out of direct sunlight. Indoor housing provides natural shade, but be sure to monitor areas that may receive direct sunlight and either shade those spots or allow calves to move out of them. Translucent hutches can trap radiant heat and actually become hotter than the outdoor temperature.
- Ventilation — Adequate ventilation requires the constant exchange of dirty inside air with fresh outside air. This constant air exchange helps reduce the transmission of airborne pathogens and provides ample air flow. Regardless of housing style, take measures to promote air flow 24 hours a day, 365 days a year. Allow ample space between hutches and open doors and vents. In calf barns, supplemental ventilation is a must.
- Strategic handling — Perform procedures such as dehorning and vaccinating early in the morning when temperatures are cooler.
- Pest control — Warm temperatures invite the added challenge of flies and other warm-weather insects and pests. Work with your veterinarian to ensure that your pest management program helps minimize calves’ exposure to disease-causing pathogens and the vermin that spread them.
Consult with your veterinarian and nutritionist to determine the best ways to help keep calves hydrated and healthy in hot weather. Visit DairyWellness.com for more management tips to help you put your calves on track to realize their lifetime potential.
1 Place NT, Heinrichs AJ, Erb HN. The effects of disease, management, and nutrition on average daily gain of dairy heifers from birth to four months. J. Dairy Sci. 1998;81:1004–1009.
2 Bateman G II, Hill M. How heat stress impacts the growth of calves. Progressive Dairyman. 2012;15:19.