Antibiotics are used for disease control. Usually they are specific for those diseases caused by bacteria or related organisms. The beneficial effects of antibiotics are due to their ability to disrupt various phases of cellular metabolism. An antibiotic will prevent bacterial multiplication, provided enough is present to attack all the bacteria present. If the amount of antibiotic is small and the number of bacteria large, the antibiotic will not produce its full effect.
Antibiotics also act by changing the intestinal flora.
In some instances the birds have become resistant, producing a change in the value of the drug. The diagnostic laboratory uses a technique known as a sensitivity test to determine which drugs are effective in treating a disease. The test actually shows which drugs are effective and those that are ineffective for treating the disease. Proper administration of medications requires that all precautions be followed as shown on the product label. Be sure that the dosage, route of administration, and required withdrawal period are observed.