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Calf-raising programs, and by association the replacement heifer program, are often poorly managed on many dairy farms. Raising newborn calves is labor-intensive any time of the year and requires even more attention during the winter months. Cold stress on neonatal calves can slow their growth rates dramatically, and research has also shown that calves subjected to slow growth for extended periods may also be less productive as mature milk cows over their lifetimes.

At the core of cold stress for young calves is understanding the concept of the “thermoneutral zone.” The thermoneutral zone (TZ) refers to that range of ambient temperatures in a calf’s housing environment in which it doesn’t need to expend extra energy to remain cool or warm. The calf is comfortable—not too hot, not too cold. The TZ for baby calves is in the range of 60 to 75 degrees Fahrenheit. In a calf’s diet, once the caloric requirements are met for maintenance needs—standing up, lying down, walking, breathing and staying healthy—the remaining calories can be used for growth. When temperature challenges occur, more calories are used to satisfy the maintenance needs of staying warm or cool rather than going to the growth process.

With winter upon us in the Northeast U.S., temperatures are most likely just above freezing during the day and well below freezing at night in most locations. These temperatures are well below the TZ for baby calves and many more calories will be needed to keep the calf warm, let alone meeting the caloric requirements for keeping the calf growing at a rate of 1.5 to 2 pounds per day.

When dairy calves are born, they have neither a functioning rumen nor much in the way of body fat, so they must quickly start consuming large amounts of calories to help bolster the immune system, get weight on, and get the rumen developing. Extremely cold weather conditions, especially at this critical time, can seriously compromise calf health.

For a newborn calf weighing 90 pounds, each 10-degree decrease below the TZ will decrease the daily weight gain by 0.2 pound per day. With no adjustment to the caloric intake from the diet, enough energy is taken away from the growing process to slow daily weight gain by 0.2 pound. The problem is compounded as the weather gets colder. When no adjustments are made to the calf’s diet to increase whole milk, milk replacer or starter feeds, growth rates diminish rapidly when the ambient temperature drops below the TZ.

On many dairy farms neonatal calf diets are designed to get Holstein calves to grow at an average of 1.5 to 2 pounds per day. These growth rates are necessary to have a Holstein heifer weighing 1,200 pounds by the time she’s 22 months old and ready to freshen. A drop in the ambient temperature of 30 degrees—60 degrees Fahrenheit down to 30 degrees Fahrenheit—will decrease average daily gain by 0.6 pound per day. For a calf whose average daily gain (ADG) is only 1.5 pounds of weight per day, this is a 40 percent drop in growth rate.

The metabolizable energy requirement for the maintenance (MEm) of a baby calf weighing 90 pounds at birth, in thermoneutral conditions, is about 1.6 megacalories per day. This is only for maintenance and not for growth. Whole milk contains about 2.44 megacalories per pound on a solids adjusted basis. Therefore, in order to meet the MEm requirement for this calf, she must consume about 0.66 pound of milk solids. This equates to 5.25 pounds of whole milk, or about 0.6 gallon. If a neonatal calf is consuming 2 gallons of whole milk per day, 0.6 gallon of that is needed for maintenance and the rest goes toward growth. As temperatures drop below the TZ, more of the solids and calories available in the milk are needed for maintenance that will take energy away for growth in the total diet.

Meeting caloric requirements for neonatal calves less than 2 weeks old can be problematic when temperatures are at or below freezing for much of the day. Young calves are barely able to consume more than 2 pounds of dry matter at that early age, and it becomes difficult to get the necessary level of calories into them. Many milk replacers must be fed at a rate of 2 pounds per day just to maintain an aggressive ADG of 1.8 to 2 pounds. When a calf is subjected to temperatures of freezing for a good part of the day, dry matter intakes of milk solids must be increased by 30 to 40 percent to fill the energy void to maintain a target ADG. In addition, calves must be encouraged to start eating calf starter grains as early as 2 weeks of age to help keep caloric intake up.

A simple solution to avoid this challenge is to move calves into a warmer housing environment. Raising calves in a space that can be kept above freezing and protected from rain and snow will go a long way toward minimizing the negative energy balance. It’s also worth noting that even in the spring and fall of the year the nighttime temperatures often drop into the 40s and 50s, which means the calves will spend part of the night below the TZ and using more calories to remain warm.

The calves born at your dairy represent the future of your dairy herd. Costs associated with the heifer replacement program on dairy farms are second only to the costs of feeding the milk cows. Management goals of dairy farmers should include raising heifer calves as rapidly as possible, getting them bred and into the milking barn in less than two years. While it’s never possible to completely avoid the negative energy balance associated with cold weather on dairy farms, being aware of and adjusting neonatal calf diets to minimize the nutrient deficiencies associated with colder weather will keep calves growing at an aggressive rate even through the winter.