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Give calves the energy they need to grow through the winter

Anne Proctor for Progressive Dairy Published on 30 October 2020

Have you ever wondered why calves don’t grow as well in the winter as they do at other times of the year?

Understanding some basic concepts on how colder temperatures impact calf growth will help you counteract the effects of winter temperatures and keep those calves gaining.

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Calves have an energy requirement for maintenance. This is the energy needed to fuel the body while the calf is at rest. The calories the calf consumes from feed supply energy and are partitioned either for maintenance or for growth. Calories are used first for maintenance. If there is energy available once maintenance requirements are met, the additional energy is used for growth.

Using the 2002 NRC Requirements of Dairy Cattle, we can calculate the maintenance energy requirement of a calf at 20ºC, which is its thermoneutral zone or the temperature at which the calf is neither using energy to keep warm nor to cool itself. The Metabolizable Energy for maintenance (MEm) requirement depends on the bodyweight of the calf and environmental factors. A heavier calf has a higher MEm. When environmental temperature drops, a multiplication factor is applied to calculate the MEm requirement.

Table 1 shows the MEm requirement of 36- and 45-kilogram calves at temperatures ranging from 20ºC to -29ºC. Notice the multiplication factor.

Metabolizable energy for maintenance

Each 1 degree decrease in environmental temperature requires an additional 0.04 Mcal of energy. It doesn’t look like much, but those calories add up quickly. For instance, at -17.8ºC, a calf needs almost twice as much energy as it did at 20ºC. This is just the energy that the calf needs to keep warm. If we expect the calf to grow, we must also supply the additional calories for that calf to use for growth.

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Calories come from the feed the calf consumes. For our 36-kilogram newborn calf, milk or milk replacer provides its only source of calories. We can calculate the calories per kilogram of milk replacer if we know the amount of fat, protein, carbohydrate, ash and moisture. We will assume 7% ash and 5% moisture in our example. Neither ash nor water provide energy but are needed in the calculations. From the milk replacer tag, we know the protein content is 26%, and the fat content is 17%. Lactose is calculated by difference using the equation:

Lactose = 100 - Water - Ash - Fat - Protein

The protein, fat and lactose are corrected to a dry matter basis by dividing each by the percent dry matter of the milk replacer powder. In our example, the 26% protein would be divided by 0.95, resulting in a protein content of 27.4% on a dry matter basis. The same calculation would be made for fat and lactose content. The energy is calculated using the formula below where crude protein (CP) is the protein content. Note: This formula is only valid for milk replacers containing only milk-based ingredients.

ME (Mcal per kg) = (0.057 × CP + 0.092 × Fat + 0.0395 × Lactose) × 0.93

The resulting ME value is in Mcal per kilogram of dry matter.

Since fat contains about twice as much energy as either protein or carbohydrate, it is logical to conclude that increasing the amount of fat in a milk replacer increases the energy content. Table 2 shows the energy content of milk replacer containing 26% protein, 5% moisture and 7% ash with varying levels of fat.

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energy supplied by milk replacer containing varying levels of fat

Each 1 unit decrease in fat content results in a reduction of 0.05 Mcal of energy, a 1% decrease.

The column on the left shows the percent of energy in each formula compared to the 26% fat product. Many people are surprised to learn that the difference in energy between milk replacers with 17% or 26% fat is only 9%. Since each 1 degree drop in temperature requires 0.04 Mcal, and each 1 unit increase in fat content provides 0.051 Mcal per kilogram, it is impossible to put enough fat in milk replacer to compensate for winter temperatures.

Figure 1 shows the amount of a 26% protein, 17% fat milk replacer needed to meet the maintenance requirement (orange bars) at varying temperatures.

Milk replacer needed for a 36-kilogram calf to support maintenance

At 20ºC, our 36-kilogram calf needs 0.33 kilogram of milk replacer powder for maintenance. If we expect the calf to gain 0.9 kilogram per day, it needs an additional 0.6 kilogram of powder or a total of 0.93 kilogram. The amount of energy needed for 0.9 kilogram of growth is constant regardless of temperature. If temperatures drop to -17.8ºC, that 0.93 kilogram of powder will only support 0.45 kilogram of gain per day.

Imagine we fed 0.57 kilogram of powder year-round. While our calf would be able to gain 0.45 kilogram per day when temperatures are warm, it would need all of that energy just for maintenance when temperatures dropped below freezing. When temperatures get close to -17.8ºC, our calf can no longer meet its maintenance requirement and uses its body reserves to keep warm. While the calf may have calf starter available to it, without a functioning rumen the calf is unable to get the energy it needs.

While older calves with functioning rumens can consume more starter to help meet their energy needs, younger calves rely entirely on the milk replacer they are offered. Be sure to provide enough energy for that calf to meet its maintenance requirements and also have energy for growth. Increasing the fat content in the milk replacer is not enough to counter the effects of cold temperatures. Instead, it is necessary to feed more powder. Going from 2 litres to 3 litres or from two feedings per day to three is a 50% increase in energy. Increasing the concentration of your milk replacer solution from 12.5% to 15% solids is a 20% increase in energy.

In addition to changing the feeding program to provide more energy, management strategies can also have an impact. Minimizing heat loss from the calf to the environment will lower the maintenance energy requirement. Dry newborn calves quickly and keep all calves clean and dry. Use calf jackets and deep bedding for insulation. Prevent drafts in buildings and repair holes or cracks in calf hutches. Make sure milk is reaching the calf at a minimum of 40ºC and offer warm water. Practice good sanitation to reduce exposure to pathogens; fighting disease uses a lot of energy.

Understanding how temperature affects maintenance requirements will help you adjust your feeding program to enable your young calves to thrive during cold weather.  end mark

Anne Proctor
  • Anne Proctor

  • Nutritionist
  • Form-A-Feed Inc.
  • Email Anne Proctor

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