It is time to change to winter bedding, bring out the calf jackets, and consider an extra feeding to provide calves extra protection from low temperatures.
A calf is born with only two to four percent of body weight as fat, which will not last long if she is forced to burn fat for heat production. Burning body fat for heat can lead to lower growth rates, compromised immune status, and even death. The need for straw bedding at this time of the year to provide warmth for young calves is true both in barns and in hutches. Unless the calf barn has supplemental heat, it should be well-ventilated but without drafts on the calf. It should also be within five degrees of outside temperatures, necessitating the use of straw bedding and calf jackets.
If you normally use shavings as calf bedding during summer, it is now time to switch to straw bedding to help keep calves warm.Michigan State University Extensionrecommends using straw bedding when temperatures are in the 40s or below. Straw bedding is ideal when daytime highs or nighttime lows are below the thermo-neutral zone for a young calf. A newborn Holstein calf has to burn energy to keep herself warm when temperatures are below 50 degrees Fahrenheit. If there is draft, wet bedding, or an immune system challenge, then the critical temperature is higher.
Straw is the best choice of bedding to provide thermal insulation for the young calf. Straw should be bedded deep enough for the calf to nestle in. This traps warm air around the calf, which will help maintain body heat. For winter months, the straw should be deep enough that when the calf is lying down its legs are generally not visible. A drawback to straw is that it tends to hold moisture, so it is important to add fresh bedding regularly and consider a layer of shavings underneath the straw to draw the moisture away from the calf. Moisture exceeding 20 percent is too high. If you kneel with all your weight in the calf bedding, any moisture on your pants indicates the bedding is too wet.
Calf jackets are another way to protect calves from losing excess body heat. The more heat a calf loses to the environment, the more calories need to be consumed in order for the calf to stay warm. The use of deep straw bedding and calf jackets during low temperatures will help young calves stay warm, resulting in improved average daily gains and immune status.
A good rule of thumb: For every 10 degrees Fahrenheit below freezing (32 F), the calf should get 10 percent more milk to meet its needs. This means that if it is 0 F outside, the calf should consume 32 percent more milk. If you normally feed 3 quarts twice a day, then adding a third feeding of at least 1.9 quarts would best meet the calves' needs. You can add more volume to the two current feedings (feed 4 quarts at each feeding), however the calf would benefit most from a separate feeding even if the feedings are spread equally throughout the day. Be careful in adding extra powder to the same volume of feeding, as too high of solids (18 percent and above) will cause diarrhea. Also, avoid adding extra fat to the milk which can depress starter intake, potentially decreasing overall caloric intake.
When caring for calves in cold climates, the use of deep straw bedding, calf jackets, and providing extra calories during cold temperatures is necessary and will result in healthier calves and improved gains.