How to keep calves growing when the weather turns cold.

Imagine that your car will go 60 miles per hour in the summer but only 30 mph when the temperature is freezing, and it will not run at all when the temperature falls to 0ºF. This is an accurate illustration of how cold temperature adversely affects rate of gain in calves.

Although I recommend jackets for calves in winter and have no doubt they are beneficial, I find no published data about jackets to evaluate the benefits versus cost. Calves need enough straw bedding to make a nest when it is cold – if you can see the calf’s legs, you need more straw. Calf starter feed with greater than 50% grain is important to develop the rumen and should be available at all times beginning on day one. In this article, we’ll discuss how cold weather impacts calf nutrient requirements and how we can change our milk replacer feeding program in winter to maintain calf performance.

Energy for maintenance and protein for growth

Nutrient requirements for calves can be divided between maintenance requirements and requirements for gain. The big picture is pretty simple: Calves need high energy and low protein for maintenance and low energy and high protein for gain. Maintenance includes basic body functions like maintaining body temperature, keeping the heart pumping and other functions to keep the calf alive. Maintenance does not include weight gain.

Requirements for energy and protein do not change at the same rate, as shown in Figure 1 for a 100-pound calf. A calf gaining 0.5 pound per day has a 37% increase in energy needs but a 190% increase in protein needs. To gain 2 pounds per day, the energy requirement increases to 277% of maintenance, while protein increases to 868% of maintenance.

Effect of cold on energy requirements

Cold temperature stops growth. When raising heifers, our objective is to double birthweight by day 56 because calves that gain at this rate produce more milk in their lifetime than calves that grow at a slower rate. I appreciate Alan Kozak making me aware of the need for more information about Jersey calves, so to illustrate the effect of cold temperature on calf performance, imagine a 60-pound (27.2 kilogram) Jersey calf with a target rate of gain of 1.07 pounds (485 grams) per day (60 pounds divided by 56 days equals 1.07 pounds per day). At 68ºF (20ºC), the calf requires about 10 ounces (283.5 grams) of milk replacer twice per day to gain 1.07 pounds per day. If we continue to feed 10 ounces of milk replacer twice per day, average daily gain (ADG) decreases to only 0.54 pound per day when the temperature drops to 32ºF (0ºC), and calves completely stop gaining weight when the temperature drops to 0ºF (-18ºC).

Options for increasing energy for the calf

We can’t meet the goal of doubling birthweight by day 56 if calves stop gaining weight, so if we are going to maintain a 1.07-pounds-per-day rate of gain, something has to change. We have two basic options to compensate for cold weather. Either we can change the composition of milk replacer to increase energy density by increasing the amount of fat (and reducing lactose) in milk replacer, or we can feed additional energy to compensate for cold by increasing the amount of milk replacer being fed each day.

Option that doesn’t work: Increasing fat in milk replacer

For the first option, and staying with our Jersey example, we’d need to create a milk replacer with 26% protein and 59% fat to maintain 1.07 pounds per day ADG and feed 10 ounces of milk replacer twice per day. That would not be an easy product to make, and I doubt calves would eat it very well. There is a myth that increasing the fat content of milk replacer significantly increases the amount of energy contained in the milk replacer. In truth, if we double the amount of fat in a milk replacer from 10% to 20%, we reduce the amount of lactose from 56% to 46%, and the energy content increases from 1,860 to 2,087 kilocalories per pound, which is an increase of 227 kilocalories per pound. But this represents only an increase of 12.2%, and since the total energy requirement increases by 23% as temperatures drop from 68ºF to 32ºF and by 42% when temperatures drop to 0ºF, it is impossible to compensate for cold by simply changing milk replacer composition.

Option that works: Increase dry matter intake

How do we compensate for cold and increase rate of gain? We increase rate of gain when we increase energy intake by feeding more milk replacer per day, much like we increase the speed of our cars by pressing on the gas pedal and “feeding” more gasoline to the engine.

So the question is, “What should we feed the calf?” Contrary to the popular myth, I do not recommend feeding additional fat in the winter for several reasons. First, calves don’t digest or metabolize fat very well. Secondly, increased fat intake typically decreases starter intake, which results in lower total daily caloric intake. Heat produced during the fermentation of starter feed is an important source of heat for calves during cold weather. Thirdly, increasing levels of fat in milk replacer reduces digestibility of feed. Finally, lactose is preferentially used for growth and fat is preferentially used to deposit body fat. French research shows that replacing fat with lactose results in increased daily gain. Research at Cornell University shows that calves fed low-fat milk replacer had 8.5% body fat while calves fed high-fat milk replacer had 11% body fat. Dairymen claim they don’t want fat heifers, yet they continue to feed high-fat milk replacers, which increases the body fat of their heifers.

In my own experience, reducing fat by reformulating milk replacer fed at a calf ranch increased daily starter feed delivered to 10,000 hutches from 17,000 to 23,000 pounds within a few days. Calves were more active, consumed more feed and more water, and 60-day weights increased as well.

Table 1 shows how cold impacts requirements for both Holstein and Jersey calves. Target ADG is 1.7 pounds per day for Holsteins and 1.07 pounds per day for Jerseys, which is birthweight divided by 56 days. Compared with the Holstein calf, the Jersey calf has a higher protein requirement at every temperature, and the increase in energy requirement due to cold temperatures is greater for the Jersey calf than the Holstein calf. At 0ºF, the total energy requirement is 142% of the requirement at 68ºF for the Holstein calf but it is 152% for the Jersey calf. Regardless of hair color, the greater impact of the cold is because a 60-pound calf has more surface area relative to bodyweight than a 95-pound calf (344 versus 281 square centimeters per kilogram, respectively).

Notice that the amount of protein in milk replacer can be reduced during cold weather because we’re feeding higher quantities per day, but the total grams of protein required is a function of daily gain. Fat content of milk replacer could also be decreased because our goal is to feed additional lactose to compensate for the cold and to keep total grams of protein and fat consumed each day constant. Dairymen could save money by feeding milk replacers with lower protein and lower fat in winter because they are feeding higher daily amounts of milk replacer, and the total grams of protein and fat needed per day remains constant.

To maximize lifetime milk production, calves should double their birthweight by 56 days old. While this goal is relatively easy to achieve during warm weather, the negative impact of cold weather slows growth rates, which makes it difficult to achieve a 56-day weight of 200% of birthweight. Which strategy is best to minimize effects of cold weather? All strategies should be used: calf jackets, deep straw bedding, calf starter with a high corn content starting on day one and increasing milk replacer intake by 20%-25% when temperatures reach freezing and increasing by 40% when temperatures reach 0ºF. Although widely repeated, feeding additional fat is not as effective as feeding additional lactose because calves don’t digest or metabolize fat very well. Feeding higher amounts of fat results in reduced calf starter intake, so daily caloric intake does not increase to meet the increased demands of cold weather. Instead, feed an increased amount of milk replacer and keep calves growing.