Food and Drug Administration released guidelines | Intent is to stop using important medications for growth promotion
RED DEER — Antibiotics were once called wonder drugs because they combatted potentially fatal bacterial diseases, but a growing list of microbes resisting treatment has become worrisome.
That concern is partly behind the U.S. Food and Drug Administration’s guidelines that were released in December to voluntarily eliminate the use of medically important antibiotics for growth promotion in livestock.
Use of these drugs to make animals grow better or to prevent disease is often criticized, said Reynold Bergen, head of the Beef Cattle Research Council.
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When antimicrobial resistance occurs among bacteria in livestock, there is concern those bugs could spread to the human population and reduce the effectiveness of drugs.
“The assumption is that there is abuse of drugs in livestock production and that is putting consumers at risk,” he said at the Alberta Beef Industry Conference held in Red Deer Feb. 18-20.
“We need these drugs to be effective so we can keep our animals healthy, and we need human drugs to be effective as well.”
Antibiotics are categorized as very high importance, high importance, medium importance and low importance to human health. Those in the highest category are rarely used to treat livestock.
Canada conducts routine surveillance of livestock and meat sold at the retail level looking for resistant bacteria. The Canadian Integrated Program for Antimicrobial Resistance Surveillance’s most recent report found significantly low levels of bacteria with resistance to antimicrobials.
Producers use ionophores for growth and feed efficiency in cattle, but there is growing pressure to remove them from the market. However, no one can show whether it would make any difference to human health if they were banned.
Denmark banned the products for routine use in 1994 and found that veterinarians eventually prescribed an increased amount of more powerful drugs. However, the Danes have also found few resistance problems in the very important drug category.
Research is about to start in Canada on antimicrobial use in feedlots, which will assess samples from cattle, manure, soil and water. The study will include DNA sequencing from resistant bacteria to see if the same ones are present in cattle and human medicine.
More research is needed on the risk to human health, said Dorothy Krysak Erickson, manager of veterinary services with Zoetis.
“Resistance eventually shows up to nearly every compound we have discovered. It happens naturally and it is very inevitable,” she said.
Why resistance occurs is not fully understood. It could be a spontaneous change to the genes, a transfer of DNA from another microbe or the result of exposure to antibiotics such as penicillin.
Resistant bacteria survive and multiply when medication is used.
“The more we use our antibiotics, the more we are going to select for these resistant bacteria that exist,” she said.
All pharmaceutical companies report drug use and resistance issues to a global database. The information goes to Health Canada’s Veterinary Drug Directorate, which uses it to track possible resistance problems.
For example, pharmaceutical companies know some resistance is occurring in mannheimia haemolytica, which causes bovine respiratory disease, also called shipping fever, and want to track how fast it is increasing. Low levels of M. haemolytica resistance to eight products were found in Canada in 2012.
Off label medications is another controversial issue.
Canada allows extra label use, in which a different dose or combination of drugs may be used to treat an infection not listed on the label. The United States has more restrictions on extra use, and in some cases off label use is illegal.
“Canadian regulations allow us a lot of freedom to work with our veterinarians and treat our animals as appropriate,” Krysak Erickson said.
Trevor Alexander of Agriculture Canada said alternatives to antibiotics exist, but they are not always as effective in real life settings as they are in the laboratory.
Supplementing feed with yeasts, probiotics and plant compounds such as tannins, phenolics and essential oils have been tried with mixed results.
“It doesn’t always work in a real setting,” he said.
Bacteriophages show promise. They are viruses that attack bacteria and have been tested since the 1930s. Most work stopped because antibiotics were so successful.
Interest in using phages to kill E. coli O157:H7 has renewed as resistance problems have increased, but little research has been done to limit pathogens that harm cattle.
Alexander said vaccines should be used in conjunction with antibiotics, especially treatments that have been developed using DNA technology.
“There are no alternatives that are as good as antibiotics,” he said.
“Vaccines actually are very good and efficacious, but probiotics, not so much.”
