Dietary alternatives to antibiotics show mixed results in ISU research review

Given the task to find and review research on dietary alternatives for sub-therapeutic antibiotic growth promotants, Wes Schweer and a team of pork-industry experts didn’t know what to expect.

“When we first started, we found thousands of studies,” admitted Schweer, a graduate student at Iowa State University (ISU).

The actual number was 24,000 research reports. After greatly narrowing the review of research, the team examined results from 830 research projects with a total of 2,019 trials. The team reading the research included ISU and USDA animal scientists, veterinarians and microbiologists.

Searchable database developed

“The main objective was to evaluate the literature to assess dietary alternatives for sub-therapeutic antibiotic growth promoters,” he said, referring to feed medications with indications for increased weight gain and feed efficiency.

“It is just a look at if (an alternative) did improve or didn’t improve performance,” Schweer added. “The project will not recommend the best alternative.”

The results of the research review were compiled into a searchable database that is available for the pork industry to use.

Producer interest in alternatives was sparked by the veterinary feed directive rules that took effect in January 2017. Antibiotics deemed medically important by FDA lost their claims for improved performance. Several swine antibiotics not used in human medicine — bacitracin, bambermycins, carbadox and ionophores — were allowed to retain these claims.

The alternatives and results

The alternatives evaluated in the research included probiotics, prebiotics, saccharides, starch and fiber, organic acids, botanicals, yeast, and copper and zinc.

Overall, just less than a third of the alternatives improved growth performance, Schweer explained. When antibiotics were included in the base diets, the positive effects of alternatives were reduced.

“Antibiotics can alter the gut profile. Since a lot of probiotics and prebiotics also do that, there is competition between the antibiotic and alternatives,” he added.

This is an important finding because antibiotics are still under veterinary supervision to prevent, control and treat enteric and respiratory diseases.

Significant differences in pig performance were found among the alternatives. The team reported the results as a percentage of trials showing an improvement or positive outcome.

Probiotics — Overall, 40% of the 311 trials using probiotics reported an improvement in average daily gain (ADG). But when antibiotics were used in the base diet, probiotics were less effective. The positive outcome dropped to 31.6%.

“Again, antibiotics change the microbial profile, which can lead to competition for nutrients between probiotics and the established gut flora,” Schweer explained.

Yeast — About 23.5% of the trials using yeast reported an improvement in ADG. Just a slight decline in a positive outcome to 22% occurred when yeast was fed with dietary antibiotics.

Prebiotics — Of the 99 trials where prebiotics were fed in the diet, 11% reported an improvement in ADG. When antibiotics were fed with prebiotics, only 3% reported an improvement. When antibiotics weren’t used in the diet, 17% had a positive outcome.

Saccharides — Of the 92 trials using saccharides, 18.5% reported an improvement in ADG. When antibiotics were fed in the diet with saccharides, performance declined; only 11% showed positive outcomes. About 21% of the trials not feeding antibiotics reported an improvement.

Starch and fiber — Of the 281 studies using starch and fiber, just 8.9% reported an improvement in ADG.

Botanicals — Plant-derived products were used in 365 trials, with 23% reporting an improvement in ADG. Only 10% of the trials feeding antibiotics in the diet showed an improvement, while 24.5% of the trials without antibiotics reported an improvement.

Organic acids — Used in 151 trials, organic acids showed a positive result in 32% of the trials. With antibiotics in the feed, only 11% of the trials had positive results, and 35.5% had positive results without the antibiotics.

Zinc and copper — When added at pharmacological levels to pig diets, zinc and copper were among the most effective alternatives. Zinc and copper produced a positive outcome on ADG in 39% of the 613 trials. Dietary antibiotics had little effect on ADG, with 37.5% of the trials showing improvement. When no antibiotics were used, 41.5% of the trials reported an improvement in ADG.

Dig into data

Anyone interested in using alternatives can dig into the data for more information, Schweer explained. The database can be downloaded and then searched for a variety of terms to isolate references to scientific articles that incorporated those terms.

For example, the data can help develop recommendations on pen size, pig age, weight and feed duration for alternative products.

A spreadsheet containing the database is available to download at: pork.org/production-topics/animal-science/.