A few years ago, I used to smile a little when my wife complained that our house was too cold at 64 F. Now, I find myself sneaking over to the thermostat and bumping it up a couple of degrees.
It is easy for us to know when we are cold, but how do we know when livestock are cold? In some situations, it is easy to see, such as if they are hunched up and shivering. Often, though, it is hard to tell when they are cold. Their comfort range is not the same as ours.
Research has shown that below a certain point, our grazing animals will increase their metabolism to produce heat. This maintains body functions such as rumination and keeps the animal comfortable.
To meet the needs of increased metabolism, the animal will consume more feed. How much extra feed they can consume is related to the quality of the feed. The more digestible the feed, the faster it moves through their digestive system, and the more nutrients they can utilize in a given amount of time.
An over-mature stemmy hay will back up the digestive system. It is slow to break down, and the animal will not be able to eat enough to get the needed energy from the hay alone. In very cold conditions, a ruminant can increase its metabolism by 25 to 30%; however, there is a limit to how much forage it can eat and digest.
Most of us are grazing animals to produce either offspring or meat we can sell. If the animal cannot meet its energy needs to stay warm, it will start breaking down body stores and lose weight. This will cut into productivity and can also become an animal welfare issue.
Research has been conducted for most classes of livestock to determine temperatures below which additional energy is required. The temperature below which an animal’s body begins to lose its normal function is called lower critical temperature. Below this temperature, an animal needs to have additional energy to maintain body heat and normal body functions.
For cattle with a dry, average winter hair coat, the LCT is 32 F. If the hair coat is wet, the LCT increases to 59 F.
Goats and horses have values similar to cattle. For sheep with 2.5 inches of wool, their LCT is 28 F. For freshly shorn sheep, the LCT is 50 F. Due to the water-shedding properties of wool, sheep are not as severely affected by rain as other livestock with wet hair coats.
Wet hair coats are not just caused by rain and snow. Animals in poorly ventilated buildings or on wet bedding are subject to the issues caused by wet hair coats also.
Moisture and temperature are not the only factors. Wind speed is also very important. The LCTs are based on windchill temperatures.
A rule of thumb for the increase in energy needed is, for each 1 F wind chill value below the LCT, the animal will need an additional 1% increase in total digestible nutrients, i.e. energy. With a wet hair coat, this increases to around a 2% increase in TDN.
For example, a cow with a dry average winter hair coat and 10 F wind chill temperature would require an additional 22% TDN (32 F LCT -10 F wind chill = 22).
Now, let us look at a wet hair coat with a 35 F windchill. For this, LCT 59 F-35 F = 24. Now we need to multiply this by 2 due to the wet coat. This cow will require an additional 48% TDN.
Even though the wind chill temperature is 25 F warmer than the previous example, this cow will require more than twice the additional energy due to the wet hair coat.
If the provided feed does not meet the energy needs of the animals, they will start to lose weight as they break down fat reserves to supply the energy needed to survive.
Weight losses are not as obvious on animals with a thick hair coat or long wool. It is easy to overlook these weight losses until other problems start to appear.
Much research has demonstrated that reduced energy intake and weight loss during late pregnancy can lead to birthing difficulties, decreased milk production, reduced weaning weights and an increased length of time to breed back.
These issues can affect performance in future years. Now, research evidence is building on how nutrition during pregnancy can affect the genetic expression of a fetus after it is born.
How do I know what to add? This question opens several new topics. To keep it short, follow these guidelines:
1). Test the nutritional value of your forage.
2). Look at charts for the nutritional needs of your animals.
3). Factor in LCT adjustments to these chart values.
4). If your forage is not supplying enough TDN to meet the adjusted chart values, look at energy options that will work on your farm.
5). Reach out to your local extension educator for help.
Finally, in addition to increasing and supplementing feed, look at improving environmental conditions with windbreaks, dry bedding and avoiding mud as much as possible.
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