by: Stephen B. Blezinger

Part 1

Over the last few weeks we've been discussing many of the issues surrounding the use of antibiotics in feeding and managing cattle. Most producers, animal scientists and veterinarians will agree that there are significant benefits to the use of the various antibiotic compounds that are currently available for use in cattle feeding programs from both health and weight gain perspectives.

However, if we are to read the handwriting on the wall, it is obvious that because of consumer concerns as well as the activities of a variety of groups who take issue with the use of antibiotics in cattle production systems, their use will come to an end or be significantly restricted in the not too distant future.

As we've discussed, there are those that believe that the use of antibiotics for the production of food animals has caused the proliferation of antibiotic resistant bacteria in humans. There are also those that perceive antibiotics as “growth-promotants” and are uncomfortable with this concept. One thing we as an industry need to clarify for the consuming public, if possible, is that in the capacity used, antibiotics are not growth promoting per se. They do not cause a shift in cellular metabolism resulting in more rapid tissue production, predominantly the increased accretion of protein (muscle). Antibiotics by and large are exactly what the name describes, they are a compound that has a negative (anti) affect on certain species of microbes, generally bacteria, that when left unchecked, cause sickness or stress in the animal which depresses its normal growth and performance. In the case of ionophores (a.e. Rumensin, Bovatec, Cattlyst), these work predominantly in the digestive system causing a shift in the bacterial population toward those species that are more beneficial and more efficient in the breakdown, production and retention of important nutrients, especially energy. They also have a depressing effect on the multiplication and growth of those bacteria that create waste (loss) in the digestive system, such as in the production of various gasses such as methane, ammonia and hydrogen sulfide. To a large degree, antibiotics simply help the animal achieve its genetic potential for growth and weight gain by keeping in check organisms that would depress this potential. As an industry, if we are to retain these tools, we must somehow more effectively communicate this concept to the consumer and clearly illustrate their safety in the production of food. This is an uphill battle, however as we are climbing a mountain of misinformation and opposing agendas.


But if we are to “face the music” and recognize that sometime soon, our access to compounds such as antibiotics will be limited we have to search for those products or practices which can be effective replacements. First we have to identify and define what specific areas in the animal we can work to improve performance. Here are a few examples:

1) Improve digestive function resulting in increased availability of nutrients that promotes health, growth (weight gain) and milk production.

2) Methods of reducing stress.

3) Methods of increasing the immune system in the animal.

4) “Natural” methods of enhancing physiological performance.

One of the primary goals we have to achieve is the continued production of food animals, in this case beef cattle, in an efficient, cost effective manner. As any producer can tell you, on a good day, profit margins, if existing at all, are very tight. Over the years there have been many occasions where the only profits that were to be recognized were those that resulted from the improved performance efficiency that came with the use of the tools at our disposal (antibiotics, implants, other feed additives). If these are taken away, the opportunity for profitable performance is lessened. Thus we have to identify suitable replacements. Fortunately there are large numbers of individuals, companies, universities and research organizations that are taking this task very seriously.

So let's start off by considering some of the alternatives. We'll begin by looking at some of the potential opportunities that are available to improve the digestive performance of the animal.

Feeding Enzymes

Enzymes are protein molecules that catalyze specific chemical reactions. The use of enzymes in the feeding industry is not new. In most cases, feeding enzymes is believed to increase the rate and extent of digestion of certain nutrients. Several digestive enzymes have been studied for use as additives to enhance animal performance with success in poultry and swine diets. In cattle, enzyme feeding is thought to help in improving fiber digestion, especially in the rumen. Especially in cattle, however, feeding enzymes to improve ruminal digestion has been a questionable practice in the past. The reasoning behind these questions came from the fact that enzymes are proteins and they would be subject to breakdown by microbial proteases (other enzymes which breakdown proteins) in the rumen and/or similar actions by proteases in the small intestine where most absorption occurs. So while there is interest in this practice, there are questions that need to be answered.

Some things to remember:

1) There are many types of enzymes that can feasibly aid in the digestive process in the ruminant animal.

2) In general the greatest possible benefit may be derived from those enzymes which can assist with the breakdown of fiber or fiber components.

3) Some of these enzymes include cellulose (breaks down cellulose), pectinase (breaks down pectins), fibrolytic enzymes (breaks down more general fiber particles), xylanase (xylan).

4) The result of more extensive fiber breakdown (degradation) is a greater release of energy and other nutrients.

Dr. Limin Kung at the University of Delaware has made some interesting observations on this subject ( Kopecny et al. (1987) reported that a cellulase enzyme complex was rapidly degraded by rumen bacterial proteases and addition to ruminal fluid had no effect on fiber digestion in the lab. Some researchers have suggested that feeding unprotected enzymes may be more useful in young calves where rumen microbial populations are not fully developed. Another study by Baran and Kmet, also in 1987 reported that a pectinase-cellulase enzyme additive improved ruminal fermentation in newly weaned lambs but not in adult sheep where the microbial population is established. Recently, there has been renewed interest in the use of enzymes in ruminant diets because some fibrolytic enzymes have been shown to be stable when incubated with protease enzymes. In 1995 Fontes and coworkers reported that several xylanases were resistant to several proteases but only one type of cellulose enzyme was resistant to proteolytic attack. There are processes which have been reported to protect enzymes from deactivation caused by high temperatures and proteinases (Olsen and Thomsen, 1991). In 1998 Hirstov et al. reported that when added to the rumen, fibrolytic enzymes maintained partial activity.

However, integrity of the enzyme is not the only criteria that should be used when evaluating enzymes for ruminant diets, because in order for them to be effective, they must bind to their substrate and catalyze reactions. Tricarico and Dawson (1999) reported that the addition of xylanase and cellulase enzyme mixtures improved the in vitro ruminal digestion of fescue hay. Zinn and Salinas (1999) reported that a rumen-stable fibrolytic enzyme supplement increased the ruminal digestion of neutral detergent fiber (NDF) and feed nitrogen (protein source) by 23 and 5 percent, respectively. They also reported an improvement in dry matter intake and average daily gain in steers supplemented with this additive. These data suggest that adding enzymes directly (in a dry form) to the diets of ruminants may improve digestion and production.

Applying enzymes directly to the feed or forage

Over the years, use of enzymes was restricted to their application on to forages at the time of ensiling. However, this mode of application has met with varying results, possibly due to the pH drop that normally occurs as part of the ensiling process. This results in an acidic environment that can degrade or deactivate the enzyme. One method to protect from or minimize enzyme degradation by rumen bacteria (proteases) is to treat feeds with enzymes just prior to feeding. When enzymes are applied to feed in this manner, binding with substrates can cause a change in the molecular conformation that may help to protect these external enzymes from ruminal degradation. Treacher and Hunt (1996) reviewed the use of spraying enzymes directly onto feeds, rather than adding at the time of ensiling, to enhance their nutritive values. This approach offers exciting possibilities for using enzymes to improve nutrient digestion, utilization, and productivity in ruminants and at the same time reduce animal fecal material and pollution. Spraying enzymes onto feeds or forages just before feeding provides increased management flexibility for feeding and bypasses any negative interactions that the ensiling process may have on enzyme performance. A number of different mechanisms have been proposed as reasons for positive effects including direct hydrolysis, improvements in feed and forage palatability, changes in gut viscosity, complementary actions with ruminal enzymes, and changes in the site of digestion. Feng et al. (1992) reported that pretreatment of dry grass with fibrolytic enzymes improved ruminal fiber digestion in the lab. Lewis et al. (1996) reported that enzymes sprayed onto a grass hay and barley diet increased volatile fatty acid (energy intermediary) production and NDF digestion. Spraying enzymes on silage has increased the release of residual sugars and rate of NDF digestion. Continued research supports improvements in animal productivity when feeds are treated with enzymes prior to feeding. In some instances, enzymes have been applied directly to the grain but in some studies enzymes were applied only to the forage component of the diets prior to mixing into a TMR. In 1999, six research papers were published documenting positive effects on milk production. More is not always better, however. Several publications have reported that high levels of enzymes resulted in lower milk yields in dairy cattle than moderate levels of enzyme treatment (Lewis et al, 1999; Beauchemin et al., 1995, Kung et al., 1999). Over-treatment of feeds with enzymes may result in blocking locations that might otherwise be available for microbial enzymatic digestion or may prevent attachment by rumen microbes. The need for more research in this area is obvious.

Evaluating the activity of enzyme additives and predicting improvement in animal performance will be a challenge for future research because of the variables. Temperature, time, substrate concentration, enzyme concentration, product reactions, cofactors, and pH, among other factors, have profound effects on enzyme activity. In addition, sources and activity of enzymes differs markedly depending on if they are extracted from bacteria or fungi. The purity of enzyme products must also be ascertained because many commercial enzymes are actually complexes of various enzymes that must work in concert to breakdown a compound such as a fiber molecule to its individual building blocks. Determining the proper ratio of individual enzyme activities relative to the targeted feed must be determined in order to optimize their effects on feeds. Unfortunately, no universally accepted methods exist for determining enzyme activity but they are usually based on release of a monomer under optimal and standardized conditions. Certainly, newer methods that evaluate enzymes should consider their optimum activities at rumen temperature and pH.

Although our knowledge base is growing we know very little about the stability of added enzymes and interactions of enzymes with components of feeds. If added during processing, enzymes must be able to withstand temperatures during pelleting or other types of processing.


Use of enzymes in cattle feeding program shows promise but still needs a fair bit of research. However, the benefits, using a “natural” product to produce a desired result (improved feed efficiency or better utilize poor quality forages) are highly desirable and can potentially play part of the role in replacing performance benefits vacated by antibiotics. In the next part of this series we'll continue this discussion and examine other products that may be useful in improving animal performance.

Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, TX. He can be reached at or at (903) 352-3475. For more information please visit us on at www.facebook/reveille livestock concepts.

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