With winter weather and lower temperatures setting in, it is time to talk about when cows feel the cold. The big factors that determine the lower critical temperature for cattle are temperature, wind speed and heaviness of winter hair coat.
Colder temperatures, higher wind speeds and lighter hair coats will increase maintenance requirements. With a good winter coat, cattle will perform normally until temperatures drop below freezing (32°F), assuming no wind. If cattle have a heavy winter hair coat, they can withstand temperatures as low as 19°F, again with no wind. When temperatures drop further or wind chill is factored in, energy requirements increase approximately 1% for each degree. An easy way to get a ballpark figure on wind chill is to take the temperature and subtract the wind speed. So, if it is 5°F with a wind speed of 10 mph, then the wind chill index is close to minus 5°F.
Rain followed by cold temperatures can cause a lot of cold stress. Wet hair coats provide virtually no protection from wind and cold. This results in onset of cold stress at much higher temperatures. A hair coat that is wet will have a lower critical temperature of only 59°F.
If facilities are not available for cows to escape the rain, wind and cold temperatures, cows use more energy to help cope with the cold. Cows in good body condition can mobilize body reserves to meet the energy demands of short-term cold stress.
In longer periods of winter weather, additional energy may need to be supplied in the ration. For example, a temperature of 10°F with a wind speed of 20 mph will result in a 30% increase in requirement for a cow that has a heavy, dry hair coat. If the cow weighs 1,400 pounds, then she will require an additional 4.5 pounds of total digestible nutrients (TDN) in late gestation and an additional 6.2 pounds TDN in lactation. This results in the need for 6 pounds and 9 pounds of corn or corn gluten feed (CGF).
Feeding these levels of corn to cows is not recommended, and sudden diet changes can upset digestion. Use CGF, soyhulls or distillers grains, as they will not cause a reduction in fiber digestion. Watch forecasts and plan for the colder weather. Do not vary rations greatly from day to day.
Cattle are hardy critters and can handle some adverse weather conditions. We as caretakers must be aware of the increased requirements cold stress can induce. Supplying windbreaks, covered housing and additional energy in the ration all will help cattle come through winter in good condition and allow timely breedup in the spring.
