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n fall and winter, most native forages and tame pastures are low in protein (unless fall rains stimulated new growth), yet many stockmen extend grazing as long as possible into winter because winter feeding is usually the most expensive part of raising cattle. Adding a protein supplement to mature, dry pastures is generally cheaper than feeding hay. Adequate protein level in ruminant diets is crucial for optimal microbial growth and function. Rumen microbes are key to unlocking the complex carbohydrates present in dried standing forage. Without protein supplementation on dry pasture, the rumen cannot adequately digest low-quality forages. Protein supplied with alfalfa hay, blocks or tubs, or by-products like distillers’ grains, can help improve digestion of low-quality forages. Ken Olson, Extension Beef Specialist, South Dakota State University, says the key number is 7% crude protein. “Requirement for the cow, even for a mid-gestation dry cow whose calf is weaned, is a little higher than that, but we’re talking about meeting the requirement for rumen microbes, so they can digest the forage. That’s our first need, before we worry about the cow,” he says. If we meet requirements of the microbes, they can break down and digest the roughage, meeting maintenance requirements of the cow. “If protein level in forage falls below 7% it limits microbial fermentation in the rumen; we can’t grow a large enough population of microbes to get the job done.” Di-
gestion slows, food moves more slowly through the tract, the cow can’t eat as much, and she loses weight. We need to know the protein level in the forage. “Cattle are selective grazers. If we clip a sample of forage it may be poorer in protein content than what they are actually eating. We come closer in our estimate by observing what they are eating, and hand-plucking a sample of those plants,” Olson says. Many native cool season grasses can be good fall and winter pasture without a protein supplement. They have more nutrients in their mature, dormant state than many tame grasses do. “Two things I advise is to watch cow body condition and observe feces--how moist/fluid or dry they are. Cattle manure in the spring or on any lush green feed is very loose; manure is liquid. This is a sign of excess protein.” The material is digested quickly, traveling through the digestive tract too fast, with some waste of nutrients. “If manure is hard and makes a pile that stacks up, this is a sign of protein deficiency,” says Olson. There’s not enough to digest forage efficiently and keep things moving through at proper pace. Ideally, manure would be moist and loose but not liquid. This is how it would generally be when forage is still green but not so lush and washy; protein level is about where it should be. “As forage goes into complete dormancy, we need to provide a supplement, but it’s amazing how well cattle do when you first put them into a new un-grazed dormant pasture. They select a diet high enough in protein that they Continued on page 36 Gelbvieh guide • Fall 2020 • Page 33
