Feed cost is the largest expense associated with feeding confined cattle. Based on cost per unit of energy, roughage is the most expensive component of feedlot diets. Although research indicates reducing roughage level in feedlot diets can improve feed efficiency and reduce cost of gains, it cannot be removed from feedlot diets without negative effects on health and performance. Nutritional management is of utmost importance when reducing feedlot ration roughage level as the risk of digestive upset increases as diet roughage level decreases. Recent research suggests the use of effective neutral detergent fiber (eNDF) and NDF as roughage indicators in feedlot diets may help feedlot managers and nutritionist better manage roughage levels in diets.

The Connection Between Roughage and Digestive Disturbances

Roughage, a necessary component of feedlot diets, helps reduce the effect of intake variations and helps manage rumen digestive function. Low-roughage feedlot diets can predispose feedlot cattle to acute and sub-acute acidosis. Kansas State University research showed the intensity and duration of rumen pH drop during an acidotic challenge increased as the level of alfalfa decreased in the diet. Total VFA concentrations also increased during the acidotic challenge as the level of alfalfa in the diet decreased.

Acidosis occurs when feedlot cattle over consume fermentable substrate (starch). Overfeeding, missed feeding, mixing errors, adaptation to high concentrate diets, and weather can all alter the intake of fermentable substrate in feedlot diets, leading to acidosis.

Acute acidosis occurs when there is an overproduction of lactic acid in the rumen, creating a rapid drop in rumen pH. While acute acidosis can result in death, it is generally characterized by a sharp drop in feed intake and poor performance. After an animal has recovered from acute acidosis, feed intake typically remains below average for the remainder of the feeding period, resulting in poor performance.

Sub-acute acidosis occurs when there is an overproduction of VFAs (acetate, propionate, and butyrate) in the rumen. The pH drop associated with sub-acute acidosis is generally less severe compared to acute cases, and it is shorter in duration. Sub-acute acidosis generally results in inferior performance and lower dry matter intake during the challenge. Acidosis challenges can also increase the incidence of liver abscesses.

Roughage intake helps prevent acidosis in several ways:

• Diet Dilution—Roughage intake dilutes the amount of fermentable substrate
  in the diet.

• Stimulation of saliva secretion—Increased roughage levels may increase chewing
  time and increase the flow of saliva to the rumen. Saliva acts a buffer against pH changes in the rumen.

• Stimulation of rumen motility—Roughage provides “scratch factor” in the rumen.

The Connection Between Roughage and Dry Matter Intake

Maximizing dry matter intake (DMI) and energy intake are important nutritional management considerations for efficient feeding of feedlot cattle. While source and amount of roughage can affect DMI in feedlot cattle, these relationships have not been fully defined. Dry matter intake decreased and feed efficiency improved for cattle fed alfalfa when compared to cottonseed hulls (Bartle et al., 1994). With increasing levels of both alfalfa and cottonseed hulls in the diet, dry matter intake increased at a greater rate for cottonseed hull diets. Oklahoma State University researchers found that increasing roughage level increased dry matter intake, but differences in feed efficiency and average daily gain where dependant upon grain type. Average daily gain and feed efficiency were optimized at 8, 12, and 16% roughage for steam-flaked corn, 50:50 steam flaked corn/high-moisture corn, and high-moisture corn diets, respectively. The interactions among roughage source, level, grain type, and grain processing all must be considered when formulating feedlot diets.

Roughage Value

The amount of roughage in feedlot diets can vary widely. A survey conducted by Galyean and Gleghorn (2001) of 19 consulting nutritionists revealed the roughage content of feedlot diets ranged from 4.5 to 13.5% on a dry matter basis. The 1996 NRC Nutrient Requirements of Beef Cattle included eNDF as a measure of roughage value. Effective NDF is a measurement of roughage fiber content and particle size. Iowa State University researchers conducted a study designed to collect a database of Iowa feedlot rations for determination of eNDF in complete feedlot diets. They observed some relationship between dietary eNDF and acidosis indicators. These relationships were weak, and they concluded that other factors such as feed bunk management, feed processing, feed presentation, and feed mixing also likely play a role in the incidence of acidosis in feedlot cattle.

Galyean and Defoor (2003) found that dietary roughage levels accounted for 69.6% of the variation in dry matter intake, while dietary NDF and eNDF supplied by roughage accounted for 92.0% and 93.1%, respectively, of the variation. The authors concluded that the percentage of NDF supplied by roughage in diets can be used to predict the effects of roughage source and level of roughage on dry matter intake of feedlot cattle.

Implications

Roughage is needed in feedlot diets to optimize dry matter and energy intake and to reduce the incidence of digestive disorders. Roughage level needed in feedlot diets is affected by numerous factors:

• Bunk management

• Feeding management

• Grain processing

• Weather

Relationships among these four factors and roughage in the diets of feedlot cattle have not yet been fully defined. Recent research indicates roughage eNDF or NDF may be a useful tool in ration formulations. These tools must be used in conjunction with the four factors mentioned previously to provide the optimum amount of roughage in the diets of feedlot cattle.