By the time you see this, the world-famous weather prognosticating groundhog Punxsutawney Phil has trundled out to do his job. We’re either in for six more weeks of winter or not. Regardless of what the rodent indicates, weather records tell us that it’s about the coldest time of year. And that means spring-calving beef cows are getting close to dropping calves.
For feeding plans, that means its important to remember that the days just before Christmas, when cows were in mid-gestation and had lower nutrient requirements, are gone. In these cold, pre-calving days, there are a couple of things that certainly require attention: 1) how weather affects the cow’s nutrient needs; 2) barns and their proper ventilation. If you’re calving outdoors, on pasture or in the woods, lack of ventilation obviously is less of an issue. It’s excessive ventilation that you’re worried about.
When cattle are in an environment where they do not need to spend energy to warm themselves (cold stress) or cool themselves (heat stress), they enjoy what is called the thermoneutral zone. The colder end of the thermoneutral zone is the “lower critical temperature.” At points below this effective temperature, a cow requires additional energy to maintain its body temperature. If cows have a dry winter coat, the threshold at which they begin spending energy to stay warm is considered 32º F.
As a general rule, when the ambient temperature drops below the lower critical temperature, cattle will experience a 1 percent increase in energy requirement for each degree the temperature, or wind chill, drops below 32º F.
As an example, if it is 26º out with no wind and a cow is dry, she will require a 6 percent increase in energy requirements (32º - 26º = 6). If you are unable to protect the cow from getting wet, the math can get ugly. A wet coat increases the lower critical temperature to 60º. A cow outside in sleet at 26º suffers a 34 percent increase in required energy (60º - 26º = 34). And because her coat is wet, instead of every degree raising the energy requirement by 1 percent, it goes to 2 percent. Her energy requirements are fully two thirds higher when wet. She can not eat enough feed to maintain her weight.
The best that can be done from a feed perspective is to increase the amount of dietary energy available to cattle during cold weather. The most direct way to increase energy is to add concentrate/ionophores to the diet. In a pinch you can allocate your hay supply, saving higher energy hay for colder times of the year. Or saving it for expected wet periods. You’ll have to make the call depending on your hay supply and weather conditions. Regardless, protecting cattle from adverse weather conditions drastically influences the animal’s feed needs and reduces your feed bill.
Temperature is not the only factor to consider. Earlier in my career, I worked in Iowa, where we worried more about air quality for cattle enclosed in barns. Up there, ensuring adequate air exchange was a critical issue. In tight barns, adequate air exchange is required to control humidity, condensation and ammonia levels. Poorly ventilated barns typically increased health challenges for the herd.
In a peaked-roof barn, the simple solution is to make sure there is an open ridge at the peak. The opening allows warmer, moisture-laden air to rise up and out of the barn. The concept applies to mono-slope barns as well. An opening high in the barn allows warm air to carry moisture out.
The trick is to allow for good air exchange without causing cold drafts. In my experience, it is better to minimize barn humidity than maximize barn temperature. You should protect cattle from the weather, but not at the expense of air quality.
Another factor to consider in winter feeding is the cow’s protein requirement. While protein requirements won’t increase in the drastic manner that energy requirements do, feeding protein is still important in winter. A cow needs protein for her growth, maintenance and fetal development if she is gestating. Moreover, rumen function is influenced by nitrogen/crude protein. Nitrogen/protein deficiencies cause reduced fiber digestion, which tends to amplify energy deficiencies during adverse weather conditions. When forage digestibility is reduced, forage intake will be limited.