Tetracyclines are a family of compounds frequently employed due to their broad spectrum of activity as well as their low cost, compared with other antibiotics. Currently, there are over 20 tetracyclines available; however, tetracycline, chlortetracycline, oxytetracycline, and doxycycline are the most common ones in veterinary medicine. In addition to therapeutic purposes, in many other countries, tetracyclines are often incorporated into livestock feed at subtherapeutic doses as growth promoters for swine and poultry and in aquaculture. For years, the use of antibiotics as growth promoters has been linked with beneficial aspects (especially increase in nutrient uptake efficiency and commercial revenue for farmers), though there is data that supports the fact that this exercise promotes bacterial resistance, allergic reactions in humans and animals, and changes in environmental microflora and bacterial populations among other detrimental effects.