Although most calves are born weighing around 90 pounds, they are a fragile, newborn animal, susceptible to bacteria and environmental stressors. Smaller dairy breeds are even more susceptible. The size of calves is just one factor that determines their thermoneutral zone. A thermoneutral zone is a temperature range at which an animal is the most comfortable, therefore extra energy is not required to simply maintain a normal body temperature. According to Jones and Heinrichs (2019) these temperature ranges are not constant and are determined by various factors including wind, moisture, hair coat, sunlight, bedding, and rumination. For calves less than a month old, their thermoneutral zone is between 55 and 70°F. Cold stress in calves can occur when temperatures remain below 50°F, which is considered their lower critical temperature (Jones and Heinrichs, 2019). When the temperature drops below this lower critical temperature, calves must use energy to support basic bodily functions and attempt to maintain their normal body temperature. According to Silva and Bittar (2019), at low environmental temperatures, newborn calves that have increased heat production to maximum levels in response to cold exposure can easily become hypothermic. In order to prevent cold stress, there are many steps that can be taken including using straw to heavily bed calf pens, increasing a calf’s caloric intake, and using calf jackets to help keep those calves warm.
A cold calf will need to use energy to try to maintain its body temperature; energy that would normally be devoted to growth and maintaining a healthy immune system. Instead of using her calories to grow, a cold and stressed calf will use her energy to simply try to stay warm, making her more susceptible to illness or even death. Silva and Bitter (2019) reported that failure to produce enough heat can lead to the development of secondary complications including chronic digestive and respiratory disorders as well as scouring and pneumonia, which can affect later performance and increase mortality. Wet calves are extremely vulnerable to heat loss. A clean, dry hair coat provides greater insulation from cold than a wet, matted coat, and calf jackets can be used to further insulate young calves (Jones and Heinrichs, 2019). Calf jackets are most useful for calves under 3 weeks of age and especially for any calves that are sick and struggling with illnesses. One of the keys to maximizing profit and keeping young calves healthy is creating an environment that keeps cold stress down, since it contributes to low performance and increased rates of morbidity and mortality in the first few weeks of life (Silva and Bitter, 2019).
When using calf jackets as another level of protection for your calves, a commonly used rule of thumb is to put jackets on calves when the ground is frozen. We are all aware of the temperature swings that can occur in Pennsylvania during the winter months. Therefore, on those days that see higher temperature spikes, jackets may need to be removed during the day to prevent the calf from getting too warm and sweating under the blanket. If the calf is sweating during the day, that damp calf will get chilled once the temperatures begin to fall at night. Sweating followed by chilling will negate the purpose of the jacket. In addition to monitoring temperature swings, the actual jacket should be monitored at least once a week to make sure that the jacket straps do not need to be adjusted to accommodate the growing calf. Leg straps can quickly become too tight and dig into the back legs of calves, easily causing open sores where straps can cut into the legs. Remember that putting a jacket on a newborn calf is not a once and done action, it requires monitoring as the calf grows and as the weather conditions change.
As calves grow and begin to consume larger amounts of starter grain, jackets are not as essential compared to those calves under a month of age. As calves consume grain, fermentation of the grain in the rumen produces heat, helping to warm the calf. Depending on the weather conditions, calf jackets can be removed once that calf is growing well and consuming grain. Waiting until weaning to remove jackets may add another level of stress at an already stressful time. Removing jackets at a reasonable time while the calf is still on milk will help them adapt to their environments now that the added protection of the jacket is removed. Remember to wash jackets in between uses to remove any built-up mud or manure to ensure a clean, dry jacket is available for the next newborn calf.
Source: Penn State Extension