This week, I’m one of four speakers on the Southeastern Montana Winter Ag Series. It’s an annual event around these parts, involving 8 communities in 5 days. I’m giving the same talk this week as I did at Cow Capital Beef Day last Friday, focusing on preparing for the calving season. We began in Jordan on Monday afternoon, traveled to Circle for an evening program, and went to Broadus today for a mid-day session. The weather yesterday left a little to be desired – single digits, above and below zero, accompanied by a stiff wind, which was busy relocating large quantities of snow. In Jordan, we had a nice discussion about the impacts of the miserable weather on cow nutrient requirements.
The range of temperatures where an animal doesn’t have to do anything “extra” to maintain body temperature is called the thermoneutral zone. The low temperature of that range is called the lower critical temperature. This temperature can vary – for example, a cow with a summer hair coat, or a wet coat regardless of season, has a lower critical temperature of 59 degrees. Cows with a heavy winter coat have a lower critical temperature of 17 degrees.
The rule of thumb is that for every degree below the lower critical temperature, a cow’s energy requirements increase by 1 percent. So if it’s 20 degrees below the lower critical temperature, the cow’s energy requirements increase by 20 percent. This could be met by feeding another 4-6 pounds of good quality hay, or 2-3 pounds of grain in this example. Interestingly, protein requirements remain unchanged during cold stress.
Just like people, cows are impacted by windchill, so the actual temperature needs to be taken into account when calculating extra feed needs during cold stress. Here’s the National Weather Service’s windchill chart. You can also it by clicking this link: windchill chart
As you can see, it sure doesn’t take much of a breeze to lower the effective temperature when you start with a pretty low number!
Tomorrow I’m off to Ekalaka and Baker, and I’m looking forward to visiting with more of my favorite people – Montana ranchers.
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