What Is Cold to a Cow?

This is the time of year when people start wondering how cold and wet the winter will be.  We do know there will be at least a few days or weeks of cold, wet weather.  The impact of this on cattle producers is that weather is a major factor for designing winter feeding programs and impacts feed expenses for the cow herd.  This could be a very critical issue for beef producers this winter, especially in light of marginal quality hay supplies.  A review of environmental impacts on cattle nutrient requirements is in order.

Tables exist for lower critical temperatures (the temperature when cattle feel cold stress) based on thickness and wetness of the hair coat.  There are also charts which show how wind speed and air temperature create an effective temperature.

A cow with a dry winter hair coat feels cold stress at about 32 degrees Fahrenheit (F).  A cow with a wet winter hair coat feels cold stress at 59 degrees.  For each degree of cold stress, the cows’ energy requirements increase by 1 percent.  A cow on a rainy 40 degree day will have the same cold stress, and thus the same increased energy requirement, as a cow on a dry, sunny 13 degree day.

If the cow has a dry winter coat and is exposed to an effective temperature of 10 degrees F, her energy requirements increase by 20%.  An effective temperature of 10 degrees is achieved by 30 degree air temperature and 20 mile per hour (mph) wind speed, 25 degree air temperature and 15 mph wind speed, or 20 degree air temperature and 10 mph wind speed.

To deal with the cold stress, the cows’ metabolic rate increases which increases the need for dietary energy, so the cow tries to eat more feed.  The cow exposed to an effective temperature of 10 degrees F will need to consume about 4 pounds more hay or 2.5 pounds more grain in order to meet this increased energy demand.  She may or may not be able to increase intake that much, especially if the hay is of poor quality.

In order to help cattle deal with the cold stress that is certainly ahead, keep a few concepts in mind.  First, reduce exposure to the wind.  Second, keep the cattle as dry as possible.  This includes having dry feeding and loafing areas.  Third, keep plenty of water available at all times.  Restrictions in water consumption reduce feed intake.  Fourth, consider feeding in the evening.  Incremental heat production from digestion is greatest 4 to 6 hours after feed is consumed, so heat from fermentation would be greatest at night when temperatures are generally the lowest.

One last point is that the problem of feeding low energy hay is corrected by increasing the energy density of the diet.  Feeding, or trying to feed, more pounds of poor quality, low energy hay will not improve energy balance for the cow.  In fact, it will probably make things worse due to the reduced rate of passage of feed through the digestive tract.  The only way to increase energy density of the diet is to add more calories.  This is done with supplemental grain, grain by-products, higher quality hay or haylage, or silage.

Cattle are hardy animals that can adapt to a wide variety of environmental conditions.  However, a few management changes can help reduce the impact of these environmental stressors and help keep cattle producing at an acceptable level.

Source: Gene Schmitz, MU Extension Livestock Specialist