Like Kerosene on a Brush Fire: Grazing Supplements Can Kick-Start Gains

by Paul Davis, Ph.D

Spring and summer often afford cattlemen the  opportunity to utilize grass and small grain pasture to put economical gain on stocker calves. This type of grazing or stockering is a long-standing practice in the beef industry. Lush growing pastures and immature small grains are often very nutritious and subsequently calves perform quite well. Gains from wheat pasture are often around two pounds per day, but permanent pastures may not perform as well depending on several environmental factors.  With record cattle prices, the question of whether or not to supplement grazing calves often arises.

Being ruminant animals, calves rely on the microorganisms that live in their digestive tracts to glean a great deal of nutrition from ingested forages. When supplementing stockers on pasture, consideration must be given to how the supplement affects rumen microorganisms. Effects can be positive, aiding the microbes in being more efficient and getting more nutrition from the forage. Conversely, supplementation with improper feedstuffs may produce negative effects and cause a decrease in forage utilization and feed efficiency. These all-important rumen “bugs” have requirements for minerals, nitrogen (protein) and carbohydrate energy. Calves also have nutritional requirements that must be met in order for them to live, grow and remain healthy. Supplementation programs and products should be used to provide mutual benefits to the calf and his rumen microorganisms, resulting in improved performance.

Provision of a salt based vitamin-mineral supplement to grazing stockers is a logical first step in supplementation. In most parts of the country, pastures may be somewhat deficient in meeting a calf’s requirements for copper, zinc, selenium, and phosphorus. Trace minerals such as copper, zinc and selenium are part of many vital functions including health and immunity. The rumen bugs also need trace minerals to function efficiently, and if properly supplemented are better able to glean the nutrition from forages. A calf that remains healthy, and is not using nutrients to battle a subclinical disease, has more protein and energy available for growth and weight gain. Small grain pastures are generally adequate, while some permanent pastures may be lacking in protein for growing calves. Forage testing is required to know for sure. Forage tests are easy and relatively inexpensive. The nutritional analysis from forage testing can provide a roadmap for supplementation. Lightweight stockers will require about 12.5-13 percent protein to gain two pounds per day. If forages test low in protein, supplemental protein is necessary or gains may suffer. When choosing a protein supplement for grazing stockers, it is important to know that forage protein is very soluble and readily used by the rumen bugs. Therefore, a supplement that is high in non-protein nitrogen is not the best choice. Oilseed meals and some corn by-products like corn gluten feed and distillers dried grains are excellent sources of supplemental protein.

Under grazing conditions, it is more likely that dietary energy will be the limiting factor to weight gain. By providing supplemental energy, the calf will benefit directly from in the increase in calories and indirectly from increased activity from the rumen microbes. Energy supplements should be based on ingredients that provide energy from soluble fiber rather than excessive starch, sugar or fat.  While excess fat can create a physical barrier that can separate ingested forage particles from the digestive microorganisms, the overuse of sugars and starches also hampers forage utilization by changing the pH of the rumen. This is described as negative associative effects and is created when rumen pH drops and fiber-digesting microorganisms are less effective at converting forage into energy. Pasture supplements that include soybean hulls, corn gluten and/or wheat middlings provide energy that is “friendly” to the rumen environment.

Feed additives such as iono­phores can improve feed efficiency and weight gain. Poloxalene, added to a feed or mineral supplement, may help reduce wheat pasture bloat. University of Florida research suggests that methionine may be the first limiting amino acid in growing cattle. Therefore, feeding rumen-protected (bypass) methionine may be economically beneficial. When done correctly, supplementation to grazing stockers can be like pouring kerosene on a brush fire as the performance response is quick and dramatic. As with all inputs, return on investment must be considered, but given today’s cattle prices most supplementation programs will provide a positive return.   

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