Lignins: Improving Animal Feeds

Lignin is a natural part of animal feedstuffs, typically making up about 10% of the dry material in alfalfa, grass, and other fibrous ingredients. Commercial lignin is also of plant origin; it is a co-product of wood-pulp. Wood chips are split into cellulose fibers and a liquor composed of lignosulfonate and wood sugars. Even though this liquor is a mixture, it is referred to by the feed industry simply as lignin sulfonate.

Lick Tanks

Liquid protein supplements are used to complement poor quality forage for beef cattle. The supplement is built around molasses (flavor,energy, and carrier) and urea (protein). Trace minerals may also be included. The liquid supplement is held in a tank that contains a partially submerged lick-wheel; the licking action of the cattle causes the wheel to rotate and deliver a continuous supply. Lignin sulfonates often replace part of the molasses in these supplements. They provide energy, are less viscous than molasses and will inhibit crystal growth which would lead to settling-out of minerals. In addition, ammonium lignin sulfonates contribute nitrogen which the cattle can convert to protein.

Rations fed to cattle in bunkers may include ingredients that are dry, dusty, and unpalatable. When this occurs, a liquid conditioner is added. Molasses is the most popular conditioner, but lignin sulfonates often are used successfully. Both products will reduce dust and bind minerals to feed to prevent segregation. However, lignin sulfonates are attractive because they are often less costly than molasses, are more fluid and easier to apply and mix, and, in the case of ammonium lignin sulfonates, contribute nitrogen that will be converted to protein by the ruminant. Palatability of lignin sulfonates is generally acceptable at levels of 4% in the ration.

About 60 million tons of animal feed are pelleted in the U.S. each year. Pelleting reduces waste, improves flavor, reduces segregation of ingredients, ensures balanced nutrition, and allows animals to consume feed with less effort. If pellets disintegrate back to meal, many of these benefits are lost. Animals regard the fines just as we regard the last bit of broken cereal that pours into our bowl at the end of a box.

Lignin sulfonates have natural adhesive properties; addition to feed prior to pelleting can double the strength of the pellet. Typically, addition of 2% lignin sulfonate will cut fines in half that are generated by handling and transportation of the pellets. Some lignins, selected specifically for binding characterisitics, will significantly improve pellet quality when used at levels as low as 0.25%. Lignin sulfonates are currently used to improve quality of pellets made for cattle, swine, rabbits, turkeys, ducks, chickens, dogs, trout, salmon, shrimp, and other animals.

Lignin sulfonate binders not only make pellets more durable, they also increase the efficiency of the pellet mill. To form pellets, feed is extruded through a metal die. When lignin sulfonate is mixed with the feed, it produces a lubricating film over the metal surface. As a result, less power is required and the extrusion rate is increased. This saves energy and reduces man-hours per ton of feed.

The lubricity of lignin sulfonates has another important benefit - it allows the feed to be steam-conditioned to higher temperatures. As feed is conditioned, it softens, eventually becoming dough-like. Before this happens, the feed becomes too plastic to push through the die holes. By lubricating the hole, lignin sulfonates reduce resistance to extrusion, thereby allowing higher conditioning temperatures to be reached. Feed manufacturers seek high conditing temperature as part of their program to eradicate salmonella.

Lignin sulfonates have secondary functions which discourage salmonella in poultry. Lignin liquors contain mannose, a sugar which has been shown to bind to salmonella and prevent it from attaching to the intestinal mucosa, thus inhibiting colonization. In addition, lignin sulfonates migrate to the ceca of poultry where they are fermented by bacteria. Establishing an active bacterial colony in the ceca tends to exclude salmonella bacteria. Although these are positive features, they are not currently commercially attractive.

Lignin sulfonates are also used to increase the milk production of dairy cows. Sugars that naturally occur in hardwood liquors will combine with feed proteins, such as soybean meal, and alter the protein so that it is not as easily digested by bacteria. The process is often described as "the browning reaction", and is, in fact, the same reaction that causes bread crust to brown.

Bacteria thrive in the cow's rumen. In this symbiotic realtionship the cow supplies the bacteria with grass, water, and a warm environment, and the bacteria digest cellulose, releasing energy that would otherwise be unavailable to the cow. To support their own metabolism, the bacteria also digest and re-synthesize protein. This is an excellent system in nature, but it creates a bottleneck for farm production. To increase milk production, more protein must be supplied to the cow. Unfortunately, when high levels of protein are fed, the bacteria begin to interfere. Their digestive enzymes break the protein down faster than they can re-synthesize it, and protein is lost. Treatment of protein with lignin sulfonates that contain wood sugars chemically alters the protein so that it is not digested by rumen bacteria and moves into the small intestine where it can be used to support milk production. In an optimized system, cows are fed both treated and untreated protein. Untreated protein supports the metabolism of the rumen bacteria while lignin sulfonate-treated protein bypasses the rumen and delivers undegraded protein to the small intestine. This leads to a net increase in amino acids available for milk production.

*Covered under U.S. Patent 5,023,091