The impact of cold stress on calves

As the temperature keeps dropping and the days get shorter it's a good indication that winter is here. As you're gearing up to keep yourself warm on these blustery cold days, make sure you give a thought to your animals as well, especially your calves.

Whether in a barn or in hutches, calves are more susceptible to the negative effects of cold temperatures than are cows and more mature heifers. The range of temperatures where calves use no additional energy to maintain body temperature, or thermoneutral zone (TNZ), ranges from about 55'-70'F, varying slightly due to age and other factors.

In general, for every 1'F drop in temperature below the TNZ maintenance requirements of the calf increase by 1 percent. Calves are especially susceptible to the negative effects of cold due to having a larger surface-area-to-body-mass ratio than more mature animals, resulting in more body heat loss with the larger surface area. Cold stress causes calves" energy to be used for maintenance rather than being utilized elsewhere in the body.

In more mature animals, fat can be mobilized to make up for this energy deficit. Calves, however, are born with low body fat reserves and excess energy must be supplied to avoid negative consequences.

Calves that are cold stressed right after birth have negative consequences from the start. Cold stress decreases the rate and delays the absorption of immunoglobulins from colostrum, though net absorption of colostral immunoglobulins is generally not affected.

Calves exposed to cold conditions also have a higher percentage of neutrophils and decreased percentage of lymphocytes compared to calves housed in TNZ and heat-exposed conditions between days 3 and 14 of exposure. This could be indicative of a delay in the development of the immune system in the cold-stressed calves.

Any delay in the immune system, be it the rate of absorption of colostral immunoglobulins or development of lymphocytes, puts calves even more at risk than they naturally are at this early period of life.

The more noticeable consequences of cold stress on calves, however, may be the decreased average daily gains. Unless adequate supplemented energy is provided, the energy used for growth in TNZ conditions will be used for maintenance.

Calves under cold stress will not grow as well as calves do in the TNZ; even a slight loss in growth can be detrimental to future productivity. A summary of calf data from Cornell found that a difference of 2.2 lbs. daily gain in the pre-weaning period resulted in 1,874 pounds more milk in the first lactation, and the trend continued in later lactations.

Average daily gain of calves must be kept optimal to ensure replacements entering the herd will have the opportunity to be as productive as possible.

Easing the effects of cold stress can be done through feeding and management practices. Feeding practices to counteract the energy lost maintaining body temperature will have the greatest effect.

When feeding milk or milk replacer, more milk could be fed at each feeding, or a third feeding could be introduced. If that's not an option, many companies sell a winter blend milk replacer that is higher in fat and carbohydrates, accounting for the energy deficit created by cold temperatures.

It's important to deliver milk as close to body temperature as possible (~102'F). This decreases the energy the calf spends to heat the ingested milk up to body temperature.

Water offered to the calf should also be delivered at this temperature and topped off multiple times a day. Increased calf starter intake also can help to ease the energy deficit in these calves.

It's important to provide an adequate starter grain ad libitum to calves starting when the calf is two or three days old. A study conducted with the same milk replacer feeding in cold and warm environments tried to measure the effects of cold stress on calves, though calves in the cold environment had a higher starter intake than calves in the warm environment.

Consequently calves were similar in growth and immune measures. This shows that as long as calves are provided adequate nutrition during cold stress periods, the negative effects can be averted.

It's also important to modify management practices to account for the cold temperatures. Calves should be kept warm and dry. This can be done by helping to dry calves after birth, and the use of calf coats especially on younger calves.

Bedding is very important in the calf area; it should be dry and ample enough to allow for "nesting" to help insulate calves.

If a calf's legs can be seen while the calf is lying down, the bedding depth is not optimal and will not properly help insulate the calf in cold weather. Calf housing should allow for adequate airflow but also protection from wind and drafts, as this can greatly impact the temperature.

Calves are very susceptible to the effects of cold stress; those effects can be very detrimental to calves themselves and farm productivity as a whole. It is imperative to analyze management and feeding practices to ensure that your calves will have appropriate housing, nutrition, and management to accomplish your preweaning goals this winter.

 — Sarah Williams,

 * References available upon request.



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