Cold stress often occurs during winter months, leading to insufficient energy intake. Stressed calves are more susceptible to disease and have higher mortality rates than calves receiving adequate energy. A thin hair coat, a small layer of subcutaneous fat and a relatively large surface area to weight ratio make young calves much more vulnerable to harmful effects of low ambient temperatures than older calves.
Calves raised in cold or outdoor facilities are most vulnerable to cold stress. Maintaining weight gain is always a concern with calves raised outside during the winter. These calves need additional energy to help maintain performance in cold weather.
A calf's performance and survivability in cold weather depend on its ability to keep a constant or nearly constant core body temperature. The Thermoneutral Zone, or TNZ of an animal is the range of ambient temperatures in which the heat produced by the animal at rest equals the heat lost. The TNZ of the young calf is generally between 50°and 70°F, although it varies with age, nutrition, wind and humidity. The calf can easily maintain a balance between heat production and loss with air temperatures within the TNZ.
An ambient temperature of about 50°F is referred to as the lower critical temperature for baby calves. Temperatures below 50°F require the calf to burn additional energy to produce heat to maintain body temperature. As ambient temperature decreases below the lower critical temperature, the calf will use its own fat stores if energy is not supplied in the diet.
Since young calves store very little fat, they can quickly become severely stressed at low ambient temperatures if adequate energy is not provided. When the calf's heat loss is greater than its heat production, the calf's body temperature drops, resulting in hypothermia. Performance of these calves can be strongly affected. Stressed calves show signs of depression, weakness, shivering and poor appetite, with severe situations resulting in death. Sufficient energy must be provided in the diet to prevent the breakdown of body tissue and cold stress in calves.
The colder it gets, the more energy the calf needs just to stay warm. In general terms, a calf's need for energy increases 1% for every degree Fahrenheit the temperature drops below 50°F. In other words, the calf requires another 200 kcal/day for every 10 degree temperature drop.
View the PDF for information on ways to increase a calf's energy intake