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Silver bullets? Alternatives to antibiotics
by James E. Pettigrew, PhD.
The livestock industry is under pressure to reduce the amount of antibiotics we use, for good reasons. As we reduce our use of these powerful tools, we must consider potential changes in diets and management that may be needed. Obviously, there will be varying degrees of reduction. But I predict we will not have the option of no change. I believe the industry can make substantial reductions in antibiotic use with little trouble. I suggest we eliminate antibiotics used strictly as growth promoters from finishing diets. This should have so little effect on performance that most producers will be unable to detect it, perhaps with no reduction in profits. Further reductions in antibiotic use will bring more challenges, requiring more-creative responses. The term “alternatives to antibiotics” may suggest low-inclusion non-antibiotic feed ingredients that do what antibiotics do. I doubt that such “silver bullets” exist. However, I am optimistic that certain physiologically active feed ingredients may modify the gut environment to improve growth performance and/or resistance to enteric diseases. These products may be useful either in the presence or the absence of antibiotics and could be more useful in the nursery than finishing phase, because of the greater challenge of keeping young pigs healthy.
Milk products. Widely used in today’s complex diets, spray-dried whey provides both lactose and proteins.
Lactose is a dietary energy source that is easily utilized by the young pig, but it also appears to favor the proliferation of certain bacteria in the digestive tract. There may be also benefits from the milk proteins, including immunoglobulins.
Spray-dried plasma. Spray-dried animal plasma is used widely in diets for pigs immediately after weaning. The specific modes of action of plasma are not known, although some evidence suggests that it affects the immune system.
Zinc oxide and copper sulfate. High levels of zinc oxide and/or copper sulfate are widespread in early nursery diets to control diarrhea and promote growth. However, we may lose the chance to feed these nutrients at such high levels because of possible environmental concerns.
Acids. Some studies have shown that acids are less beneficial in diets that include milk products than in simpler diets, and that observation has diminished the interest in use of acids in the United States.
Egg immunoglobulins. Hens can be immunized against specific porcine pathogens, and immunoglobulins from their eggs prepared into a feed additive are often combined with spray-dried plasma. Data suggest that these products may improve performance and resistance to disease.
Mannan oligosaccharide (MOS). Derived from yeast cell walls, this produces a small increase in growth rate in weaned pigs. Its mode of action is unclear, but it may prevent a pathogen binding to the gut wall and/or affect the immune system.
Direct-fed microbials. Often called probiotics, these are fed to animals to encourage the bacteria’s proliferation in the gut. They have been available for decades and continue to be significantly researched.
Fructo-oligosaccharide. These are preferred substrates for certain intestinal bacteria, primarily Bifidobacteria, which are often considered to be desirable. Evidence suggests it causes a change in gut microbial populations and may improve performance.
Herbs, spices, botanicals and essential oils. These serve several functions, including enhancing palatability and feed intake, altering microbial populations in the digestive tract, and serving as antioxidants in the tissues.
Competitive inhibition products. Bacteria are harvested from the intestine of a healthy adult animal, propagated in the laboratory and then given orally to a young animal, often immediately after birth.
This allows “desirable” bacteria to occupy the binding sites on the gut wall and prevent attachment of pathogens. Significant challenges remain to obtain approval to market such products.
Fermented liquid feeds. In Europe, there is considerable interest in using fermented liquid feeds. Containing acids produced during fermentation and live bacteria that perform the fermentation, these feeds combine these benefits of the ingredients. To avoid fermentation of crystalline amino acids, it may be necessary to ferment the major ingredients rather than the complete feed.
These products and others appear promising, but in several cases, we need a clearer understanding of their effects in commercial production.
There are no silver bullets, but we have a rich supply of physiologically active feed ingredients that may improve pig performance and health.
About the author: Dr. Pettigrew is a professor of animal science, specializing in swine nutrition, at the University of Illinois. This article has been condensed for space, but the entire paper and references are available from NSR.
