by Sally Colby

When the weather turns cold and humans add more layers of clothing to stay warm, consider what it takes to keep young calves warm.

Like humans, calves have a thermoneutral zone – the range of temperatures in which the calf can regulate its body temperature to remain comfortable in the environment without expending extra energy.

When temperatures drop below a certain point, it’s difficult for neonatal calves to maintain a consistent body temperature. Young calves experience the effects of cold weather sooner and more severely than older animals. Dr. Sarah Morrison, researcher at the Miner Institute, said in temperatures ranging from 59º F – 82º F, calves generate some metabolic body heat and have a normal exchange with the environmental conditions they’re experiencing. When temperatures drop below 59º, calves start to feel the effects of cold weather.

Keeping calves warm in winter

Calves provided with clean, deep straw bedding can stay warm and dry, which preserves body heat for important metabolic functions. Photo by Sally Colby

Approximately 2% of a healthy newborn calf’s body weight is brown adipose tissue (BAT), which helps the calf maintain a normal body temperature. BAT is concentrated in critical spots of the calf’s body, including between the shoulder blades and around the heart, kidneys and major blood vessels. When temperatures are low, BAT is activated and helps to warm the blood.

Young calves have a larger surface area relative to their weight, which means they’re prone to rapid heat loss in comparison to older animals that have more mass and less surface area. Young calves also lack the insulating properties of white fat and sufficient hair coat to help regulate their temperature.

Once temperatures are consistently below 59º, it’s more challenging for the calf to maintain its body temperature. Changes in temperature, relative humidity and wind speed throughout the day also influence calf comfort.

Although the importance of colostrum is mainly viewed for its immunoglobulin properties, colostrum has a high percentage of fat and protein to jumpstart the metabolic process and help the calf produce heat.

Morrison said the calves born after a difficult birth are more susceptible to the cold. Such calves often have impaired vasoconstriction and often exhibit muscle shivering and reduced activity. Additionally, calves challenged with health issues or stress such as transportation or group housing may not thrive, especially in cold weather.

In cold weather, the time between birth and thorough drying can make a difference in the calf’s ability to stay warm. Calves born in the cold will take longer to stand and may be slower to drink colostrum. A wet hair coat means more rapid loss of body heat. Drying the calf allows its hair to provide protection from the cold. Calves can be warmed in a warming box, but immersion in a warm water bath followed by thorough drying is a quick and efficient alternative for warming chilled calves.

The goal of a calf-raising program is to double birthweight by 56 days of age. When calves consume milk or milk replacer, the energy and protein is first used to meet maintenance requirements. If calves aren’t receiving adequate nutrition for maintenance sufficient to maintain body heat, the nutrition program must be adjusted to allow for growth.

Feeding during early calfhood impacts the pre-weaning period and has lasting implications for the animal as she begins lactation. Collins referenced a Cornell study showing that calves born in temperatures below the thermoneutral zone had higher maintenance requirements, resulting in potentially less growth and first-calf heifers that produce less milk.

For calves under three weeks of age that are not yet consuming starter feed, nutrient increase can be accomplished by providing more milk or milk replacer per feeding. In some cases, it may be beneficial to add a third feeding, preferably later at night. Alternatively, increase solids concentration without changing the total volume. Collins cautioned against increasing solids too much because this requires providing sufficient clean water, which can be challenging in winter. Another way to increase energy density is by feeding milk replacer blended for winter.

Consider water temperature at mixing and feeding times. Mix milk replacer according to bag instructions, monitoring the water temperature so milk is delivered to the calf above her body temperature. If young calves are fed cool milk when outdoor temperatures are low, they expend energy to heat what they’re drinking. Calves provided with properly warmed milk are also more willing to drink. An on-demand hot water heater in the milk preparation area can help maintain a consistent temperature for milk replacer.

When calves begin eating calf starter regularly, rumen development begins and calves generate more heat through fermentation and can tolerate more extreme weather.

Collins said a rule of thumb for starter and water is for every one part starter, the calf should consume four parts water. If a calf is eating one pound of starter, provide at least a half-gallon of water and make sure water is available throughout the day to promote starter intake. Providing warm water, especially for very young calves, will result in higher water consumption. Without sufficient water, rumen development is slower and the feed conversion rate is reduced.

Calf housing should be managed for the most prevalent environmental challenge. The goal is to minimize the severity of extreme weather conditions while providing adequate ventilation with fresh air to avoid stale pockets and noxious gas buildup.

Calves should always be on clean, dry bedding to help maintain body heat. Ideally, there should be at least three inches of bedding between the calf and the floor. Concrete or rock surfaces absorb the calf’s body heat and may require additional bedding. Collins said the structure of wheat straw provides insulation qualities that help hold body warmth. Calf bedding should be sufficient to ensure the calf can “nest” deeply to maintain warmth.

Based on the University of Wisconsin-Madison nesting score, a score of 1 means the calf is on top of the bedding and its legs are completely visible when the calf is lying down. A score of 3 is achieved with bedding that’s deep enough to hide the calf’s legs. A score close to 3 is ideal.

Calf jackets can help maintain the calf’s body heat and raise the nesting score. A calf with a jacket equals a score of 1, so a score of 2 can be accomplished with sufficient bedding and the addition of a calf jacket to maximize retained body heat. When days are warm and nights are cold, check the hair coat under the calf jacket to be sure there’s no dampness from perspiration. Wet hair, even under a jacket, quickly leads to a chilled calf.

When temperatures drop, be sure calf personnel know how to dress warmly so they don’t have the urge to hurry through calf care tasks and risk missing issues that can lead to chilled calves.