Cold winter weather presents some additional challenges to keeping dairy calves healthy, comfortable and growing. The biggest challenge is the increased nutritional requirement for body maintenance, especially for dairy calves in unheated facilities. Nutritional maintenance is what is required to keep all body systems functioning normally while maintaining a healthy body temperature and neither gaining nor losing weight. Cold weather nutrition requires understanding the concept of lower critical temperature. Lower critical temperature is the lower boundary below which the animal needs additional nutrients, primarily energy, to meet maintenance requirements. If the nutrient level is not increased, then the animal must burn fat reserves to meet the need. The lower critical temperature for calves from birth to 7 days of age is 55°F. Between 7 and 30 days of age, the lower critical temperature is in the 48 to 50°F range. For older calves, the lower critical temperature increases to 32°F.
Cold weather nutrition for young calves is critical for a couple of reasons. One is the fact that calves are born with only two to four percent of their body weight as fat. This means that if diets are not meeting maintenance needs, the calf can quickly burn up fat reserves. Calves stop growing and worse, the immune system of the calf becomes compromised leading to sickness. Livestock depend upon an insulating hair coat to provide protection from the cold and to moderate that lower critical temperature. That is one reason that the lower critical temperature for older calves is higher as compared to younger calves, but it takes time and energy to grow and develop that hair coat. Breed of calf will also influence cold weather nutritional requirements because small breed calves, for example, Jerseys, have approximately 20% larger surface area per unit of body weight than a large breed calf, such as a Holstein.
A rule of thumb for feeding calves housed in unheated conditions in cold weather is that for every 10°F below 32°F, the calf needs 10% more milk to meet its nutritional needs. At 0°F, this requires 32% more milk. The best strategy to meet this need is to add an additional feeding. For example, if normally the calf is fed 3 quarts twice a day, add an additional 2-quart feeding. If milk replacer is used, it should contain at least 20% protein or in the 26 to 28% range for accelerated growth programs. The fat content should be at least 15%, and higher fat content milk replacers of up to 20% fat are preferred as temperatures decline. The solids content of liquid milk replacer can be increased in cold weather from a typical 12.5 to 16%, but be careful in going above this content as diarrhea can result, and recognize that the calf may not be receiving enough water. Always offer calves clean, fresh water in addition to milk or milk replacer. Another key to feeding calves in cold weather is to provide all liquids at 105°F target temperature for consumption. With regard to free-choice water, this means offering water several times per day in cold weather. Beginning a few days after birth, offer calves free access to a calf starter grain mix with a minimum protein content of 18%.
There are a couple of other management practices that help to increase calf comfort and aid in keeping calves growing and healthy in cold weather and these involve bedding, providing extra layers of cold protection and ventilation. Straw is the best bedding choice for calves. To provide the most effective thermal insulation, it has to be deep and dry. Calves can nestle down into the straw during cold weather. The goal is to provide enough bedding so that when the calf is nestled down, you don’t see its legs. Dryness is important to keeping the calf warm. Test the dryness of the bedding by kneeling down into it. If your knees get wet, more bedding is needed. Calf jackets offer a good option to add another layer of insulation and cold protection for calves, especially calves under a month of age. Calf jackets should have a water repellent outer shell, an insulation that wicks moisture away from the calf, fit the calf well, be easy to wash and dry, and constructed to withstand outdoor environments. Do not forget about ventilation during winter months in closed structures. The goal is to provide adequate air turnover to prevent ammonia accumulation while avoiding any direct drafts on the calf. A general recommendation for winter weather is four air exchanges per hour.
Cold weather calf care requires more time and labor, but it is necessary to keep calves comfortable, healthy, and growing.