For calves, the thermoneutral zone is that temperature range in which no additional energy is expended in the maintenance of body temperature. Until calves reach 4 weeks of age, this thermoneutral zone is between 10°C and 25°C (50 – 77°F), and from 4 weeks of age until weaning, this zone expands from 0°C to 25°C (32 – 77°F).
As the temperature drops further from the calf’s lower critical temperature (the lowest temperature in the thermoneutral zone), more energy is required to maintain body temperature. This results in a diversion of energy and nutrients away from immune function and growth. Adjustments in housing and feeding management should help compensate for these increased requirements.
Best approach for winter feeding
One school of thought is to provide extra energy through additional fat. However, dietary changes stemming from single nutrient alterations such as fat, forces the digestive system of the calf to adapt in order to meet these changes -- an energy-intensive and physiologically demanding challenge. One of the studies conducted previously at the Grober Young Animal Development Center was to assess how calves performed when fed a regular (R) milk replacer (26/18) versus one with extra calories from fat (HF) (26/30); (Figures 1 & 2). There was no difference between intakes of the milk replacer between trial groups. However, grain intake was less throughout the trial for calves on the high fat milk replacer. It is important to note that increasing a calf’s access to grain for extra calories is typically not as efficient as is using milk replacer during this stage of growth (where the digestibility of milk replacer is 97% or greater). Adequate grain intake is not only very important in developing the rumen, it ensures that the transition at weaning is less stressful.
Moreover, feed: gain (the measure of how much feed it takes to gain 1 kg. of bodyweight) was less in calves consuming regular milk replacer (1.60 R; 1.71 HF). Meaning less R milk replacer was needed to gain the same amount of weight as the HF milk replacer (Figure 2).
Figure 1 Body weight difference in calves fed a regular milk replacer versus a high fat milk replacer.
Figure 2 Grain intake for calves on regular milk replacer versus the high fat milk replacer.
Amount and frequency of feedings
Adjusting a calf’s feeding program to compensate for changes in weather should be done gradually and carefully. Providing extra calories through a balanced diet that they are already accustomed to drinking, should take into account the fact that the increased amount of milk fed should be done so as an extra meal (or two), and not by increasing the size of the meals being fed.
Incorporating Acidified Milk Replacer as part of a winter feeding program will help increase the accessibility of calories and nutrients from each meal, allowing more energy to be diverted to where they are needed most. Acidified Milk Replacer provides nutrients that have been partially hydrolyzed, meaning some of the larger proteins have been broken down to smaller sizes that are more readily digestible by the calf. This “facilitated digestion” enables the calf to use less calories for digestion, and divert more of the calories they derive from their feed toward maintaining body temperature, a robust immune system, and steady growth.
Detecting cold stress
- Calf may be shivering or have noticeably rapid breathing
- The temperature and color of excessively cold hooves or muzzle show that blood is being diverted from the extremities
- Decreased body temperature: normal body temperature is at 39°C (102.2°F), cold stress begins at 38°C (100.4°F)
Avoiding cold stress
The energy demands for maintenance of the calf can be decreased through winter management practices such as blanketing, keeping the calf and bedding clean and dry, providing adequate straw for nesting, and providing ad libitum warm water. These steps along with an adjusted feeding program will help your calves stay healthy and have strong growth through the winter months.
Source: Grober Nutrition GroFacts