Keeping your calves cool and comfortable in the summer
Reducing heat stress in calves may not be the top concern during the 'dog-days' of summer, but it should be high on the priority list. Certainly, the milking herd needs to be tended to and managed so they are comfortable and can maintain milk production levels. But, what affect does very hot weather have on the well being of a calf? The consequences won't be noticed immediately as with milk production, but the health and growth rate of calves under heat stress are at stake.
Heat stress occurs with high ambient temperature, high relative humidity and excessive radiant energy that prevent adequate heat loss by animals. Although used as a reference for heat stress in dairy cows, the Temperature-Humidity Index (see table*) can still be fairly relevant and meaningful for dairy calves as well.
*Modified from Dr. Frank Wiersma (1990), Dept. of Ag. Engineering, U of AZ.
Calves do best when the optimal thermal environment is between 55 to 78°F in still air. Above 78°F, calves must burn more energy to drive off heat from the body by sweating and increasing respiratory rate. There is reduced feed intake and less of the nutrients consumed are devoted to growth. A further consequence is that calves can then experience a rise in body temperature (103 to 108°F can mean very sick calves), rapid dehydration, and a weakened immune system. Signs of heat stress in calves include: reduced movement, decreased feed intake, increased water consumption, desire for more shade, rapid respiration/panting, open-mouth breathing, lack of coordination.
The following are some management practices to keep calves healthy and to have acceptable rates of gain during hot and humid weather:
- Make housing adjustments and other changes that will lower the ambient temperature to help prevent elevated calf body temperature. If housed outdoors, calves should be able to move out of the elements and away from drafts.
- Perform stressful activities (such as moving, grouping, handling, vaccinating, dehorning) early in the morning.
- Feed fresh grain everyday to ensure good intakes during the hot weather.
- Supply ample amounts of cool, clean, fresh water to prevent depressed feed intake. Water helps with dehydration and also helps cool the calf internally. Weaned dairy heifers consume approximately 1 to 1.5 gallons water per 100 pounds body weight. When it's hot, a heat-stressed calf can consume 3 to 6 gallons of water per day.
- Use sand bedding to keep calves cooler. Clean, dry sand also helps control fly populations, compared with straw or sawdust.
- Increase airflow and air exchange to provide adequate fresh air that is free from noxious gases and airborne particles that can directly affect the calf's immune system. Improper ventilation can cause respiratory problems, reduced feed intake and conversion rates, and have long-term effects. Hutches need to have good air flow in and around them. In enclosed facilities, if natural cross ventilation is not possible, then a total air exchange every two minutes through a mechanized system of fans is a must.
- Shade. A study conducted at Missouri (Spain & Spiers, 1996) found that calves housed in hutches without shade had a higher afternoon skin temperature than calves housed in shaded hutches. Therefore, it is advisable to put hutches in the shade or construct a temporary shade over hutches (14 feet or higher to allow for good airflow). Keep the feed and water in the shade.
- Flies. A prime area for fly/maggot growth is immediately beneath the feed and water buckets, especially with outdoor calf hutches. Clean the bedding out regularly in the summer to really control fly populations. Improve drainage around the hutches to eliminate water for maggot growth.
There can be economic consequences to not managing heat stressed calves properly. A slower rate of gain means a longer time before that calf gets into the milking string. Calves and heifers are an expensive enterprise in a dairy operation and they represent the dairy farm's future. Their care and management should be a high priority during the hot summer months.
Published in Dairy Star May 14, 2010