While this winter hasn’t been one for the record books in terms of snow fall, Mother Nature has been sure to remind us that she’s in charge by dropping the temperatures to well below freezing recently. Most producers have been through cold snaps before and are aware of the challenges they present, frozen water sources, increased feed requirements, and keeping a closer eye on the herd to make sure nothing goes awry.
Properly understanding what resources we have and how much of an adjustment to make, is critical to properly manage herd nutrient requirements during this time of increased demand.
Let’s start by looking at what cold does to energy needs.
Cattle in general do pretty well with cold temperatures, especially if they are carrying average condition, their winter coat has developed, and there is no moisture they have to deal with. An average conditioned cow with a dry winter coat of 0.7”-1.0” doesn’t normally see an increase in energy need until the temperature drops below 32°F. The chart below developed by Dr. Rick Rasby cow/calf production specialist at UNL, gives the Lower Critical Temperature (LCT) for beef cows with different body condition, coat condition, and coat score.
|Heavy Winter, >1.0”||27°F||19°F||11°F||61°F||53°F||45°F|
Once we know the LCT for our animals, we can figure out what level of cold stress we have by subtracting that number by the windchill index for the day.
|Wind Speed, mph||Temperature °F|
Cold Stress = LCT – Windchill Index. For example if we have our average condition cows with dry winter coats, the LCT is 32°F. If the temperature is forecast to reach 0 degrees with 15 mph winds, then the windchill index is -15. So 32 – (-15) = 47. I had to revisit some math skills on this one, but you did read that right, since we are subtracting by a minus we actually end up adding the two numbers together. Our cold stress factor is -38.
Studies have shown that for each degree of cold stress a cow faces, they increase their energy requirements by 1%. So in our case, we need to increase our fed energy by 38%.
For example, if under normal conditions our herd is requiring 12 lb of TDN (energy) per head per day, we need to increase our ration to have 47% more, or 8 lb more TDN/hd/day. We figured that number by taking 12 x 1.47.
The cows are being feed grass hay which tested at 57% TDN, so that’s an increase of just over 14 lb/hd/day more on a dry matter basis. To find that number we just divide our 8 lb TDN increase by 0.57 and come up with 14 lb of hay on a dry matter basis.
Now since most people don’t dry out their hay before feeding, we need to adjust that number one last time. We can figure that hay is around 88% dry matter, so we again divide our 14 lb/hd/day by 0.88 and come up with just under 16 lb. So our herd this week is going to need an additional 16 lb of hay per head per day.
At this point, we have to feed our grass hay at 39 lb/hd/day to meet energy requirements. If we really push, we can get an animal to consume 3% of body weight daily for a ration. That 39 lbs. is right at the upper limit of a 1,300 lb animal and is probably pretty unrealistic. A better option here would be to provide a higher energy hay, like alfalfa for the week, or give free choice to the grass hay and keep a close eye on animals to make sure they are handling conditions ok.
If that didn’t thoroughly confuse you, Dr. Rasby has a great webinar on the topic you can find at beef.unl.edu and search “Caring for Cattle in Cold Weather” in the upper right hand corner of the page.
You can also call your local extension office for personal assistance working with your operations ration balancing and nutritional requirements.
-Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce. He is based out of the Cedar County Extension office in Hartington. You can reach him by phone: (402) 254-6821 or email: firstname.lastname@example.org .