Dairy Feeding - The Last Straw
Posted: August 8, 2005
The drought that has plagued many parts of Pennsylvania has started nutritionists and producers to seek out forage alternatives. Straw is high in fiber and low in protein, energy, and mineral content. The 2001 NRC lists wheat straw as having 73% NDF, 8.8% lignin, 4.8% crude protein, 47% TDN, 0.30% calcium, 0.10% phosphorus and 1.50% potassium on a dry matter basis. The challenge is that straw is not straw is not straw. At Penn State, the digestion of straw was measured in cannulated cows. Ten wheat straws, 2 barley straws, and one oat straw sample were evaluated. Samples came from various regions of PA, WI, MI, and IN. Differences in the pliability of the straw were observed and some samples were so tough that when squeezed, it hurt! Imagine how it feels in a cow’s mouth and why she might want to sort it out! The dry matter digestibility of the straws varied between 25 to 40% after being in the rumen for 48 hours.
Appreciating some of the limitations of straw as a forage alternative, it does have some positive attributes when used correctly. Straw can be used to provide fiber, without taking up much space in the diet. These particles are buoyant and stay in the rumen, stimulating cud chewing. A pound of straw has 2 to 3 times more lignin per pound than corn silage. Rations containing low fiber forages or low in overall forage may benefit from chew fiber added to the diet and to help restore normal rumen function.
To use straw for high producing cows, it must be processed correctly. The particle length should not exceed 1 to 2 inches in length to avoid sorting by the cows. The low protein level in straw makes it a good fit with rations containing a lot of high protein haycrop forages that also contain protein that is highly soluble. Diluting this protein fraction can reduce the amount of excess nitrogen excreted in the urine. It is recommended that straw be limited to 1 to 3 pounds per cow for early lactation and high producing animals. Milk yield, milk components and dry matter intake need to be monitored to ensure that straw is not having a negative affect on animal performance.
Another critical time for rumen health is at calving. Dry cow and fresh cow diets are a common place to feed straw. The advantage is a consistent source of fiber that does not bring in a lot of minerals common to more conventional hay crop forages. This allows the nutritionist to formulate ration mineral levels, especially phosphorus and potassium, to requirement levels. However, maintaining dry matter intakes during this period are critical. Never start feeding high levels of straw to these animals. Start off by feeding 1 to 2 pounds, monitor intakes, and observe refusals for evidence of sorting before moving towards higher inclusion levels.
Straw does have its negatives when feeding cows. Its high fiber content can limit intake. The low energy level of straw can have a negative affect on fresh and high producing cows, if not used properly. Because the NDF digestibility is low, there is a high rumen fill factor. Depending on the source of straw, palatability and sorting can be a big problem. Straw is not cheap and availability may be an issue in some areas.
Incorporating straw into dairy rations is a decision that should be based on specific needs of the cows, ability to reduce the particle size to avoid sorting problems, and justified in terms of economics. Straw can quickly turn into a liability if implemented incorrectly.
Gabriella Varga, Distinguished Professor of Animal Science, Dairy & Animal Science
Virginia Ishler, Extension Associate, Penn State Dairy Alliance, Nutrient Management and, Penn State University Dairy Unit Manager, Dairy Alliance is a Penn State Cooperative Extension Alliance
Phil Anderson, PAS, Independent Consultant, Anderson Dairy Management, Emlenton, PA