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Lush green grass presents nutritional challenges for cattle
May 2, 2017
URBANA, Ill. – It is a little counterintuitive: Cattle standing knee-deep in spring grass may not be getting the nutrition they need from the lush young forage.
“During the winter, most cattle are fed a balanced ration of dry forages, grains, and co-products,” says Travis Meteer, University of Illinois Extension beef cattle educator. “Then spring comes along and cattle are put out to grass. While green grass solves certain problems associated with winter feeding – manure, pen maintenance, calf health, and labor demands – it can cause nutritional issues.”
Meteer says spring grass presents three major challenges.
Dry matter. Young grass can be below 25 percent dry matter, making it hard for the cow to consume a sufficient amount to meet energy demands. At 20 percent dry matter, a lactating 1,400-pound cow with average milk would need to consume 138 pounds of fresh grass per day to meet her energy requirement. Higher milking cows will need even more. “In most cases, the cow fills up her rumen between 100 and 125 pounds,” Meteer says. “Physical fill can be a limiter on performance when grazing washy grass.”
Protein/energy balance. Lush forages are often high in protein but have only moderate energy content (fats, sugars, and other carbohydrates). When presented with this type of diet, rumen microbes will break down the excess proteins to produce energy, leading to ammonia byproducts that can enter the bloodstream.
Meteer says excess protein has been well documented by the dairy industry as a detriment to reproductive performance. “Some researchers argue that excess protein is not a problem. I would suggest that producers must have adequate or above-adequate energy in the ration before excess protein is okay. Even then, I would prefer if excess protein was mostly in a rumen undegradable form,” he says.
Meteer notes that protein/energy balance problems may have physical symptoms that producers can watch for. “I have observed cattle panting after a few days feeding on lush, green grass. It was not due to heat stress either; the temperature was in the high 60's. These cattle were panting because they needed more oxygen. Red blood cells carry oxygen to organ cells, and they also carry ammonia away from the cells to the liver. The panting I observed was due to too much ammonia in the system. I challenge you to watch your cattle on lush, green grass.”
Fiber. Low fiber content of immature forages results in very high passage rates and an unsatisfied cow. “It seems odd that cows would be unsatisfied while knee-deep in green grass. However I have observed this several times,” Meteer says. “Cows will readily consume a low level of dry grass hay with lush pasture. This can help the dry matter problem and add fiber.”
While there are many solutions to remedy this short-term problem, the main goal needs to be supplying cattle with a balanced ration. Meteer suggests delaying turnout until grass matures a bit more, supplying palatable, dry-baled forage that is low or moderate in protein (not alfalfa hay), supplementing with grains (not over 0.5 percent of body weight), or grazing only the top one-third of the grass plant.
As a final thought, Meteer says, “Turnout frequently coincides with breeding season. Make sure you are balancing your pasture ration so cows breed-up quickly and don't fall out of your breeding season.”