We have all seen the powerful images of beef cattle encrusted with a layer of snow during a blizzard. These pictures have probably made us envious of the cows’ ability to withstand the environmental conditions. However, how do these types of conditions affect the energy requirements?
In reality, we need to consider several factors to determine the exact response, but we can use equations published in the Beef NRC to at least estimate response and calculate the amount of additional supplement required.
Lower Critical Temperature
All animals have a thermo-neutral zone for temperature (not too hot or not too cold). The Lower Critical Temperature (LCT) represents the temperature at which cattle start to experience stress. For example, if a cow has an LCT of 40° F, then when temperatures drop below this threshold, we will need to increase supplementation.
What factors into LCT? Several things have an impact, but hair coat and body condition probably have the biggest factor. Fleshy cows with more condition can typically tolerate the colder temperatures better than a thin cow. Similarly, cows in dry conditions have a better tolerance to cold temperatures than cows in wet or muddy conditions. The following table shows this relationship based on type of hair coat (heavy winter, winter, fall, or summer) and environmental condition (dry or wet).
Lower Critical Temperature (°F) for Beef Cows – Coat Condition and Thickness
|Dry Coat Condition||Wet or Muddy Coat Condition|
Windchill and Cold Stress
In order to determine the response to cold stress, we need to calculate the windchill based on temperature and wind speed. (Table 2)
Now that we know the LCT and the windchill, we can calculate the impact on cold stress by using the following equation:
Cold Stress = LCT – Wind Chill Index
We can then use this value to determine the increase in energy requirements by applying the thumb rule that for each degree of magnitude of cold stress, we need increase energy requirements by 1%.
For example, let’s assume we have a cow in average body condition with a dry coat. According to our first table, that cow would have a LCT of 19° F. Now, let’s assume we have a temperature of 10° F with a wind speed of 15 mph. This gives us a windchill index of -7° F. This gives us a cold stress of 26 (19- (-7)) or in other words, this increases energy requirement by 26%.
Windchill Index for Cattle with Winter Coats (°F) Temperature (°F)
Additional POET® Distillers Grains Required (pounds/hd/day) Temperature (°F)
Many different variables affect the animals’ response to cold stress. However, this simple calculation using only temperature and wind chill highlight the potential deficiency in nutrients that cold stress can cause. As Table 1 clearly shows, cows in good body condition and a dry environment can tolerate cold stress the best. If cattle get wet or muddy, the ability to withstand colder temperatures drops very quickly and we need to provide greater supplements in order to maintain performance.
We can also use these tables and equations to determine more subtle temperature differences. For example, in Table 3, if we dropped in temperature from 15 to 10° F and had similar wind speed of 15 mph, we would increase the POET® Distillers Grains supplementation by approximately 0.90 lb/hd/day. This type of consideration can prevent poor performance as weather conditions change.
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*These results are not a guarantee of nutritional value, as laboratory results are influenced by factors beyond the control of POET Bioproducts.