September 15, 2002


 Natural antimicrobials look promising

Posted Sept. 1, 2002

Natural antimicrobials may prove effective in increasing growth and combating disease, according to AVMA Annual Convention speaker Dr. Christopher Chase, a professor at South Dakota State University's Department of Veterinary Sciences. Early studies show promise, offering hope for a meat industry that is increasingly urged to avoid antimicrobial drugs.

Concerns over the rise of antimicrobial resistance have sparked an interest in investigating the use of natural products to improve health and growth. According to Dr. Chase, who addressed convention attendees on July 14, three products look promising: genistein, conjugated linoleic acid, and distiller's dried grains with solubles.


Genistein, an isoflavone derived from soybeans, is a non-nutrient that has been shown to play an important role in preventing heart disease and cancer. Various test tube studies have illuminated other beneficial effects. In particular, isoflavones can act as antiviral agents, able to inhibit herpes simplex virus 1, pseudorabies virus, bovine herpesvirus 1, poliovirus, the rhinovirus that causes the common cold, and the astrovirus that causes viral gastroenteritis.

Now, new, unpublished work shows that genistein can inhibit the replication of porcine respiratory and reproductive syndrome virus. It also decreases the replication of cytopathic strains of bovine viral diarrhea virus, which are responsible for 5 percent to 10 percent of cases typically seen in the field.

Conjugated linoleic acid, a fatty acid derived from the required nutrient lineoleic acid, is another promising natural product. It has both an anti-inflammatory effect and an impact on the immune system. Studies show that it can suppress tumor necrosis factor and nitric oxide, increase the number of CD8 cells, and decrease the number of CD2 cells. "It modulates the immune system to give us what we want in terms of a more balanced response," Dr. Chase said.

Finally, recent work with a co-product of the distillery industry, distiller's dried grains with solubles or DDGS, is already proving beneficial. Some studies in poultry suggest that DDGS may contain growth factors that enhance growth, reproduction, and feed intake. Other researchers observed improvements in litter size and pig survivability in sows fed a diet containing 5 percent corn DDGS, compared with sows fed a standard diet.

The grains are also proving useful in combating porcine ileitis, which cannot be treated with subtherapeutic doses of antimicrobials and is expensive to treat with therapeutic doses. Reports indicate that adding 5 percent to 10 percent DDGS to growing-finishing pig diets can minimize the adverse growth performance effects of ileitis and cut mortality rates by at least 50 percent on most farms.

Researchers speculate that DDGS's effects may be a result of the grain's high insoluble fiber content. This high content may prevent pathogenic organisms from attaching to the gut or serve as a nutrient source for other beneficial bacteria.

Only time will tell whether these natural products will prove to be effective, offering an option for farmers who wish to keep their meat antimicrobial free. If they do, however, they will also prove profitable. Organic meat products, produced with livestock feeds lacking growth-promoting antimicrobials, are the fastest growing market in the meat industry.