Cold and your cattle

It’s pretty remarkable that warm-blooded animals can survive the extreme cold they sometimes must. The practical cattleman will not learn anything from this article to lighten the burden Old Man Winter puts on man and beast. It is intended to give an appreciation of some of the factors that affect the animal (and man) in the cold.

The normal core temperature for cattle is somewhat higher than for humans, 101.5 degrees Fahrenheit vs. 98.6 F. The cow is stressed if it goes below 100 F. Apparently that is beneficial to the function of the rumen, the stomach that ferments the cows food. This fermentation process involves growth of microorganisms that can turn plants the cattle eat into material which can be digested as it passes through the rest of the animals digestive tract. These microorganisms convert cellulose to simple sugars and some plant proteins into amino acids the cow can absorb and use which without fermentation would pass through without contributing to the cow’s nutrition.

A continuing supply of feed is very important for the animal because the fermentation supplies a lot of heat, which helps keep the animal warm in winter. Of course it also contributes heat the cow must loose in warm weather, too. The cow has a hard time getting rid of heat in summer, because, unlike humans and horses, but like many other animals, it does not sweat. Heat is lost by the bovine through evaporation of water in the lungs and breathing passages. A cow is most comfortable at 40 F. That’s why they are apt to be frisky when it is a little chilly.

One thing that helps conserve heat in dry cold weather is the hair. It helps to constrain the movement of warm air around the cow. The cow can (involuntarily) constrict the capillaries in her skin and prevent warm blood from flowing to the surface better than humans. So the surface temperature will be much lower than internal temperature when under cold stress.

Temperature is one factors in cold stress of healthy, well fed cattle. There are two others, wind chill and wet. Wind chill is familiar, we humans experience it when we walk around a corner from a still area to one where a wind is blowing. We generally seek to avoid it, and since we are relatively free to move where we want, don’t experience it much unless forced to work outside in windy cold conditions, like farmers and sailors must.

We are conscious of the effect of wet, too, but perhaps a little basic science will help understand why it is so potent. Water has a very high heat capacity, that is it takes a lot of heat to warm it, about ten times as much as an equivalent weight of iron. Strange, but true. If a warm object is in a dashing rain the water that runs off the animal (or object) is warmed, and that heat must be supplied from within the animal if the animal’s core temperature is to stay up where it belongs.

A second, even more substantial factor is that if the object is wet, water will evaporate from its surface, not just at the end of the rain, but constantly. Evaporation requires energy to separate the molecules of liquid water to allow it to become a gas. A huge amount of energy is required to evaporate water, about five and a third times the amount of heat required to warm the water from freezing temperature to boiling temperature (32 F to 212 F). This goes on all the time the animal is wet, since the skin cannot be allowed go below freezing temperature. The animal can’t avoid it. If the rain turns to snow, the evaporation goes on until the animal is dry. Dry snow is not as hard on the animal as rain, because it does not melt much, held off the animal’s skin by its hair.

Remember the heat you loose by sweating? And the effect of coming out of a shower in a cold room? It’s the same principle. The cooling is due to evaporation of water from your skin. The animal living outside must, in effect, sweat when it rains in addition to the heat that is carried away by water washing over it. And it has a lot of water retained in the hair which must evaporate before its skin is dry. A wet bovine in a heavy rain or somewhat below freezing temperature is in a pretty grim situation.

But what about a calf born into the snow? All the above apply. It needs to get a drink of colostrum as soon as possible to get digestion started as soon as possible. Colostrum is very energy rich. The calf has another adaptation, too. They have a brown fat specialized to produce heat (as do other animals, including humans). It has extra mitochondria, and a special chemistry that allows heat to be generated. It is not an unlimited supply of energy, but something the calf can call on when needed.

The best thing for your animals in the cold is to be able to get out of the wind. A shelter from the rain would also help. This is just common sense to the cowman, but maybe this discussion will help understand more about it.