Use Straw in Cattle Rations, But Carefully
Posted by Unknown in Cattle and Livestock, Hay, Silage and Forage on Sunday, 9 September 2012
When trying to determine how much straw can be used in winter rations for cows, remember straw is a low-energy, low-protein feed that isn't as digestible as hay or green feed, says Juanita Kopp in Alberta Agri-News.
On average, the forage beef specialist with Alberta Ag, Food and Rural Development, says a cow can consume 1.25% of its body weight in straw dry matter (DM). Thus a 1,400-lb. cow could consume 17.5 lbs. on a DM basis, or 19.9 lbs. on an "as-fed" basis if the straw was 90% DM (17.5/0.9 = 19.9 lbs., calculation adjust for moisture content of the straw).
"Near the end of gestation, rumen capacity is reduced by 12-13% because the growing calf takes up internal space," she says. "Straw-based rations shouldn't be fed at this time or once the cow starts to lactate. Save your best-quality feed for this time."
In order of preference, cattle will eat oat straw before barley straw, followed by legume straws, and wheat straw, she reports. The quality of legume straw can be extremely variable. The more leaves on the stems the better, but it can be very coarse and of poor quality. Coarse stems are also harder to dry down, so molds may be present.
"Cattle prefer straw that's aged a year or more," Kopp says. "It's slightly more palatable and digestible."
She says processing doesn't improve straw quality, but can increase daily straw intake. But to prevent malnutrition, impaction, poor conception rates and lower milk production, it's important to supply adequate amounts of energy, protein, minerals and vitamins to pregnant cows' winter rations, she adds.
Treating straw with anhydrous ammonia is one way to improve its crude protein content (CP) and digestibility. She says a Manitoba Ag and Food study found CP content of barley straw went from 5.1% to 9.4% when anhydrous was applied at 3% of forage dry matter.
"There are a number of protein and energy supplements that can be used to increase the protein content in winter feed to meet intake requirements," Kopp says.
These might include a good energy source, such as cereal grains or good quality pellets or cubes. Protein can also be supplemented by feeding canola or soybean meals. If using pellets, producers should request a nutrient analysis, including both protein and energy values.
In feeding straw-based rations watch for impaction problems. When the weather turns cold, cattle will try to keep warm by increasing intake. As straw isn't easily digested, it doesn't pass through the animal quickly enough and can become impacted, which can result in the death of the animal.
"Straw and grain are high in potassium (K), and a ration high in K can cause a magnesium deficiency that results in winter tetany," Kopp says. "Winter tetany is similar to grass tetany or milk fever. Limestone or magnesium oxide should be added to the ration to prevent this deficiency."
-- Juanita Kopp, 403-742-7901 or juanita.kopp@gov.ab.ca
