What happens if there is a partia l or full ban on feeding subtherapeutic antimicrobials? There is no easy answer, but researchers are working to find alternatives.

The jury is still out on how well the options will work and their effectiveness, but more data is becoming available everyday.

“There isn’t one product yet that will do everything an antimicrobial will do in feed,” says Paul Sundberg, DVM, vice president of science and technology for the National Pork Board. “In some cases, using antimicrobials in the right manner is like having an insurance policy — you don’t know the effects unless you don’t have it.”

Sundberg would like to see the U.S. Food and Drug Administration conduct a risk assessment on all anti_microbials and alternatives for use in pork production.

Most producers use antimicrobials to improve feed efficiency and promote growth. “There are more opportunities for antimicrobials to benefit young pigs. Therefore in looking for alternatives, you would expect that same trend,” says John Lopez, manager of swine business development for Chr. Hansen.

Lopez says that producers need to look at other management aspects as well. These include weaning age, piglet processing techniques to minimize pathogen introduction and overall biosecurity measures. Those factors and more were considered dur_ing NPB-funded, on-farm, antimicrobial-alternatives research trials.

Let’s take a look at the seven types of antimicrobial alternatives used in the research.

1. Probiotics are live microbial feed supplements that benefit the pig by improving the bacteria balance in the gut. The most common ones include Lactobacillus, Bacillus and Streptococcus, the yeast Saccharomyces cerevisiae, and a combination of those organisms.

Proponents contend that feeding probiotics to pigs may improve animal performance and intestinal digestibility, but reports are variable. Research indicates:

  • The results of feeding pigs Lactobacillus spp. are inconsistent. Some reports show that feeding Lactobacillus improves growth performance in nursing pigs, weaned pigs and growing pigs; and it decreased finishing costs by 17 percent. However, other studies show opposite results.
  • Using Bacillus also is variable. Improvements in growth rate and feed efficiency are seen in nursery and grower pigs. Improved nitrogen retention, but not nitrogen digestibility was observed for growing pigs. However, other reports show no effect on digestibility.
  • In one early study, adding Clostridium butyricum to grower-pig diets resulted in improved feed conversion.

2. Prebiotics are indigestible carbohydrates that can enhance animal performance by stimulating growth of beneficial intestinal bacteria. Common ones include oligofructose, fructooligosacchaaride and insulin. Prebiotics also can be fed in combination with probiotics. These are known as synbiotics.

By improving the intestinal environment, prebiotics may lead to improved pig performance.

  • Feeding a synbiotic containing fructooligosacchaaride and Bifidobacterium longum improved feed efficiency in early weaned pigs.
  • Nursery pigs fed fructooligosacchaaride showed improved average daily gain.

3. Organic Acids are fed individually and as blends. Some of the more common ones used in swine diets are formic, acetic, propionic, butyric, citric, malic and lactic acids.

Organic acids have an antimicrobial activity. The contention is that organic acids improve overall pig performance by reducing microbial competition with the pig for nutrients. Organic acids also improve protein digestibility and may enhance overall feed digestion and utilization.

Studies show organic acids enhance performance in young pigs, particularly early weaned pigs.

  • Feeding formates or formic acid, fumaric acid and citric acid improves average daily gain and feed efficiency of weaned pigs. The greatest effects occur during young pigs’ growth rather than in finishing.
  • Organic acids improve digestibility and absorption of proteins, minerals and other nutrients.
  • In growing pigs and sows, formic acid or formates are the most effective in improving average daily gain and feed-to-gain ratio. Fumaric acid comes in third here. 

4. Enzymes can help the pig break down components of its feed, letting it obtain energy from complex carbohydrates that would otherwise be indigestible. Research shows variable animal response to enzyme additives. The variations may be due to differences in the enzyme source, diet, enzyme interactions with dietary ingredients, the pig’s age and health status.

One of the more common enzymes is phytase. Feeding phytase enhances phosphorus digestibility in feed, which reduces the need for dietary phosphorus supplements and can reduce phosphorus excreted in manure.

These studies showed that phytase will increase weight gain and sometimes increase feed efficiency in pigs on several diets. Adding phytase to grain/oilseed-meal diets improves the digestibility and bioavailability of dietary phosphorus. Its effect on protein digestibility is variable.

Another common group of enzymes help carbohydrate degradation. These include amylase, glucanase, cellulase, xylanase and glucoamylase, and tend to produce variable pig performance.

5. Herbs are used as additives in swine diets, but some perform better than others. Some natural remedies contain compounds that can have antiviral or antibacterial effects on pathogens and antidiarrheal effects on pigs, probably by enhancing the immune response. Herbs also may improve feed intake by enhancing diet palatability.

6. Immune Modulators many enhance the action of the immune system and promote disease resistance in weaned pigs.

Three immune modulators were tested during these research projects.

Spray-dried plasma.

  • Fed at weaning, spray-dried plasma can significantly improve pig growth and feed intake.
  • Feeding spray-dried plasma may prevent pathogen attachment to the intestine and can decrease mortality in pigs challenged with E.coli.
  • It may provide immune protection to the pig, which lets nutrients be used for growth rather than for immune system activation during mild infections.

Egg-yolk antibodies.

  • Studies show that feeding chicken egg-yolk antibodies to early weaned piglets reduces diarrhea incidence and mortality, and improves animal performance.
  • Data about the ability to inhibit disease is variable.

Conjugated linoleic acid.

  • White-blood-cell counts tend to increase, with the greatest gains occurring in specific populations of lymphocytes after 42 days of feeding CLA.
  • CLA has produced improved feed efficiency and gain in grow/finish pigs. However, the data are variable, as other studies have found little improvement in growth performance, feed intake and feed efficiency in weaned pigs.
  • Feeding CLA to pigs can improve carcass characteristics by increasing lean muscle mass and decreasing subcutaneous carcass fat.

7. Carnitine is a naturally occurring compound found in the muscle tissue of humans and other mammals. Research suggests that adding carnitine to swine diets may result in improved pig performance and carcass characteristics.

  • Weaned pigs supplemented with L-carnitine had increased feed intake and improved average daily gain.
  • Feeding carnitine to growing pigs can result in greater lean-muscle deposition and reduced backfat.
  • Dietary carnitine improves performance and reduces carcass-lipid accretion in early weaned pigs.

Keep in mind, this is a snapshot of antimicrobial alternatives. As you can see, the results are variable, but some are more promising than others. With all of the controversy surrounding antimicrobials, it’s wise to keep an open mind about other options. 

Editor’s note: For more specifics on each research project, go to www.porkboard.org or contact Mark Boggas, DVM, the National Pork Board’s animal science director, at (515) 223-2606.