Ivan Rush: Winter nutrition in cold weather
February 7, 2011
As I start to write this a couple thoughts come to mind. The thermometer reads minus 5, and is projected to go to 15 below with wind chills nearing 40 below. I feel for those who are calving now; it requires a tremendous amount of work and shelter – even then death loss, frozen ears or tails can occur in a very short period of time if calved outside.
Much has been written on the effect of cold stress, energy and feed requirements pertaining to the cow. While calculations provide guidelines, practically speaking, ranchers feed as much good quality forage as cattle will eat along with increasing supplement levels because in severe cold, cattle are not able to eat enough forage. Let’s assume the lower critical temperature of a cow is 20°F. – in other words, the point the cow will start to sacrifice added energy to keep warm. Assuming she is further exposed to -20°F., that’s a 40-degree deficit. If Total Digestible Nutrients (TDN) requirements increase 10 percent for every 10-degree deficit, it pencils out to 4 lbs. of added TDN; if the forage contains 60 percent TDN, the cow would need an additional 7-8 lbs. of very good quality hay. Waste should also be factored in.
Some data indicates that cold stress increases calf birth weight, however it is not clear why this occurs. Data from the USDA Meat Animal Research Center near Clay Center, NE, found that cold stress increased the blood flow to the uterus, which increased nutrient flow and as a result increased fetal growth. It is not clear how long the cold stress needs to be present, or at what stage of pregnancy cold stress occurs to significantly affect birth weight. At one time I felt it had a larger effect if it occurred in the early part of pregnancy, but data does not substantiate that thought.
The second thought, that much has been written about, is the increase in nutrient demand as cows approach calving, and then after calving. A cow’s intake increases 25 percent after calving. If she consumed 30 lbs. of feed before calving, it will increase 7.5 lbs. (37.5 lbs. total) after calving. The good news is that if she was consuming a ration of 10 percent protein and 50 percent TDN, she consumed 3.0 lbs. of crude protein before calving, which is considerably higher than her requirement of near 2 lbs. of crude protein. Her TDN consumption would have been 15 lbs. before calving; after calving, 18.7 lbs., which should meet her requirement to maintain body condition and provide a good level of lactation.
These calculations work well if harvested feeds are weighed at feeding and feedstuffs have been analyzed for nutrient content. Often this is not the case. The bottom line is that body condition is indicative of nutrient intake. Still, the lag time is such that cattle may lose a half of body condition score (35-40 lbs.) that goes unnoticed until it is too late. At that point, it is very difficult to economically regain this condition in early lactation.
Lice will start to show their effect, especially as the weather starts to warm. Lice build up hurts cattle performance, causing fence or corral reconstruction as cows rub against existing structures. A heavy infestation on cows can cause a buildup of lice on young, suckling calves. Many good products are available as a pour-on that will treat both the biting and sucking lice. Back rubbers are beneficial, but pour-on or spraying gives the best control.
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If cows have been grazing winter range or crop residues such as corn stalks, they have been consuming forages practically devoid of any carotene that is converted to vitamin A. If a source of vitamin A has not been offered through a mineral or protein supplement, or high quality alfalfa hay, then liver reserves may be running low. This is usually not a problem as the feed industry offers a high level of Vitamin A in supplements. If commercial supplements have not been offered, Vitamin A can easily be offered in a mineral supplement. If the cow is consuming somewhere around 3 oz. per head daily (0.2 lbs.), then the mineral would need to have 175,000 IU of vitamin A per pound. Most will contain 200,000-400,000 IU per pound. Calves that are deficient in vitamin A will be weak and slow to start and are often born with eye problems.
Best of luck in calving and hopefully this extreme cold will break so calving can be more enjoyable. Those that have switched to May calving are most likely smiling now and enjoying a full and restful night of sleep.