No Silver Bullets to Replace Antibiotics

There are no silver bullets in the arsenal of growth promotion and herd health products being tested as possible alternatives for antibiotics.

There are no silver bullets in the arsenal of growth promotion and herd health products being tested as possible alternatives for antibiotics.

Rather, should antibiotic use be curbed or eliminated, it is more likely that pork producers will rely on a combination of technologies and physiologically active feed ingredients to maintain pig health and performance, says Jim Pettigrew, swine nutritionist at the University of Illinois.

“As we reduce our use of these powerful tools, we must consider potential changes in diets and management that may become needed, or become more important, when we use less antibiotics,” Pettigrew told swine veterinarians attending their annual conference earlier this year.

Pettigrew focused his comments on physiologically active feed ingredients that may replace antibiotics, or possibly be used with lower levels of antibiotics.

But, before proceeding, he stressed, “An appropriate response to reduced use of antibiotics is much broader than feed ingredients, and includes such things as production systems (pig flow, all-in, all-out management), biosecurity, sanitation, vaccination and disease eradication.” He suggested that restricting antibiotic use may make disease eradication or an emphasis on genetic disease resistance more attractive alternatives.

Pettigrew says we must be clear about why we use antibiotics, which he compartmentalizes into three distinct areas — growth promotion, prophylaxis (to preserve health and prevent spread of disease), and therapeusis (treatment of disease).

“It appears to me that in practice the distinction between growth promotion and prophylaxis is often unclear. Eliminating growth promotants is a much lesser challenge than eliminating antibiotics altogether,” he continues. “I believe it is in the best interest of the livestock industry to clarify that distinction. There is data that suggests that we solve most of the resistance problems if we eliminate antibiotics as growth promotants in finishing.”

The Illinois nutritionist remains a strong advocate of the prophylactic use of antibiotics in pork production. “One of the ways we will protect prophylactic use is to use them responsibly,” he says. “I think it will be easy to convince people that we should treat sick animals with antibiotics. We may need to document a specific disease threat on each farm to justify our choice of antibiotic regimen. But in my view, I think it will be very, very difficult to convince people we should use antibiotics to make pigs grow faster.”

Alternatives to Antibiotics

Pettigrew says the term “alternatives” to antibiotics may be misinterpreted. “It may suggest low-inclusion, non-antibiotic feed ingredients that do what antibiotics do. I doubt that such ‘silver bullets’ exist,” he states. “However, I am optimistic that certain physiologically active feed ingredients may be useful in modifying the gut environment in such a way that they improve growth performance and/or resistance to enteric diseases. We are in the early stages of a major (research) thrust on alternatives to antibiotics.”

The focus of the research is aimed at improving animal performance and, perhaps, their overall health. “We may do that, to some extent, by altering the microbial populations in the digestive tract,” Pettigrew says, adding: “We now believe that part of the effects of antibiotics, part of the growth promotion and disease prevention, has to do with microbial populations in the digestive tract.”

There are many related questions that could shed light on the mode of action of antibiotics and their alternatives. “They are likely to be more useful in the nursery phase than in the finishing phase because of the greater challenge of keeping young pigs healthy,” he says.

Given those contingencies, Pettigrew offers a preview of physiologically active feed ingredients and their potential:

  • Milk products: “When we first started moving away from simple corn-soy diets, adding complexity to pig starter diets, the first thing we added was dried whey and we continue to use large quantities of it,” he notes.

    Whey provides lactose and proteins. Lactose is a dietary energy source that is easily utilized by young pigs, but Pettigrew points out that it also appears to be a pre-biotic — a dietary ingredient that stimulates the growth of certain bacteria in the digestive tract. “It appears to stimulate the growth of Lactobacilli and other bacteria that are sometimes considered beneficial in the gut,” he explains. “And, we normally use whey proteins, which of course contain immunoglobulins (antibodies). I think lactose may be unusually important in starter diets.”

  • Spray-dried plasma: Sometimes described as “the magic ingredient,” spray-dried plasma is widely used in diets immediately after weaning. “The specific modes of action of plasma are not known, although some evidence suggests that it affects the immune system,” Pettigrew says. “A meta-analysis (many experiments thrown together), showed that the inclusion of spray-dried animal plasma increased the growth rate by an astounding 27%, on average. Few technologies in animal production are so powerful.”

    He offers this caveat, however: “We only use it for a short time; we can't continue to get that benefit forever, so that's one of the things that limit the ability to substitute for antibiotics.”

  • Zinc oxide and copper sulfate: Widely used in early nursery diets for controlling diarrhea and for growth promotion, these products could be restricted or eliminated because of environmental concerns.

  • Diet acidifiers: Some studies have shown that acids are less beneficial in diets with milk products (lactose). “There has emerged a concept that lactose is converted to lactic acid in the stomach, and therefore mimics the effects of acids,” he explains. Although not well understood, Pettigrew and others are investigating the concept. “I do think that the acids are very promising,” he adds.

  • Egg immunoglobulins: Hens can be immunized against specific swine pathogens and the immunoglobulins (antibodies) from their eggs serve as a feed additive that provides passive immunity to specific diseases. “We have some evidence that these products improve animal performance,” Pettigrew observes. “Although the evidence at this point is somewhat limited, I think it's an exciting idea.” (See related story on page 18).

  • Mannan oligosaccharide (MOS): “This product derived from yeast cell walls produces a small but clear increase in growth rate in weaned pigs,” explains Pettigrew, citing his study which recorded a 4.5% growth rate advantage. Although the mode of action is unclear, some speculate that MOS prevents a pathogen from binding to the gut wall and/or affects the immune system in some way.

  • Probiotics (direct-fed microbials): These products are fed in an attempt to multiply specific bacteria in the gut. Although the products have been available for decades, response to their use tends to be sporadic. “Maybe we need to learn how to manage them a little better,” he adds.

  • Fructo-oligosaccharide: Inulin, a long chain of fructose molecules, can be broken down to smaller oligosaccharides, the preferred substrates for certain intestinal bacteria often considered to be desirable. This pre-biotic is considered to be beneficial to gut microbial populations and may improve performance.

  • Herbs, spices, botanicals and essential oils: The various functions attributed to these products in animal diets include enhancing palatability and therefore feed intake, altering microbial populations in the digestive tract, and serving as antioxidants in the tissues. Although the amount of research surrounding these products is expanding, their benefits have yet to be substantiated.