AntiMicrobial/AntiBiotics Resistance in Livestock


Table of Contents


Antibiotics are antimicrobial substance that inhibits the growth and replication of a bacterium or kills it outrightly. When administered at a certain dosage they kill the bacteria but do not harm the animal being treated. Antibiotics were given to animals for various reasons including disease treatment, prevention, control, growth promotion/ feed efficiency. By the 1950s Antimicrobial Growth Promoters (AGPs) were advocated when antibiotics were found to enhance animal performance in Feed-to-Weight ratio for Poultry, Swine and Beef cattle. For many years the positive effects of this practice was championed while the negative consequences went undetected.
Thus, in the livestock sector antibiotic usage fell into two distinct areas:
⦁ The treatment of diseases,
⦁ Performance enhancement.


One of the things that can predispose to the emergence of antibiotic/antimicrobial resistance is incorrect usage of the antibiotic. When an antibiotic is given incorrectly, it results in the survival of one or more of the target bacteria. These bacteria then have the potential to develop resistance and, if they do so, their survival will be favoured the next time the same antibiotic is used and the resistant bacteria may then become the dominant form of that particular bacterium in that animal. Antibiotic resistance can occur through each of the following ways:

⦁ Making the Wrong Choice

There is a whole host of factors that the veterinarian has to take into account when choosing which antibiotic to use in a particular disease situation. The correct choice maximizes the likelihood of a successful treatment outcome. Thus, it is important to seek, and then follow, your veterinarian’s advice on antibiotic choice and usage. It is important to understand that an antibiotic is not the definite point of call for all health challenges in animal production. Antibiotics are for bacterial infections and have no effect on viral infections.

⦁ Giving the Wrong Dosage

Use of an antibiotic at a lower dosage than that intended can favour the emergence of resistance. If we weigh out antibiotic for feed or water administration we must be sure that this is done accurately. In addition, for water medication it is important to know what volume of water the weighed amount of antibiotic goes into. Most times the dosage is written at the back of most antibiotics, it will benefit the administrator to understand what is written or seek professional help.

⦁ Incorrect Length of Treatment

Getting the correct amount of antibiotic into an animal requires administering it at the correct dosage for the correct number of days. If we shorten the period of treatment then some of the disease causing bacteria can survive with an increased possibility of antibiotic resistance emerging. A common mistake, be it with animals or humans, is to assume that because there has been an improvement in clinical signs we can stop the treatment. If we do this we increase the possibility of bacteria surviving the treatment and increase the likelihood of antibiotic resistance emerging. In addition, for many diseases this scenario also favours the occurrence of relapses.

Understanding the Basics of Antibiotic Resistance: International Hatchery Practice Vol.30.3
Bonnie M.M and Stuart B.L. Food Animals and Antimicrobials: Impacts on Human Health. Animal Society for Microbiology.

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