Melengestrol is a steroidal progestin and antineoplastic agent which was never marketed. An acylated derivative, melengestrol acetate, is used as a growth promoter in animals. Melengestrol acetate (MGA) is one of six steroidal hormone growth promoters approved for use in Canada and USA. These products are used to improve growth rate and feed efficiency, as well as to suppress estrus in beef heifers (CFIA 2008). They are not approved for use in any species other than beef cattle meant for slaughter. MGA is the only drug of its kind that is administered in animal feed, and its labelled dose in Canada is 0.4mg per heifer per day (CFIA 2008). A mandatory withdrawal of 2 days before slaughter is applied to any animal that is administered MGA.

Monensin is an antibiotic produced as a byproduct of fermentation by Streptomyces cinnamonensis and belongs to a family of drugs known as polyether antibiotics or ionophores. The drug was approved by FDA for the prevention of coccidiosis in turkeys, chickens, quail, cattle, goats, calves (Coban, Rumensin). The exact mechanism of monesin action is unknown, however there are several hypotesis, which includes the inhibition of K+ transport, the inhibition of the transport of carbohydrates across the host cell membrane, the interruption host cell invasion by sporozoites, etc.

Cocarboxylase is the coenzyme form of Vitamin B1 present in many animal tissues. Thiamine pyrophosphate (cocarboxylase) is the active form of thiamine, and it serves as a cofactor for several enzymes involved primarily in carbohydrate catabolism. Pancreatic cells obtain thiamin from their surroundings and enzymatically convert it into thiamin pyrophosphate (TPP) in the cytoplasm; TPP is then taken up by mitochondria via a specific carrier the mitochondrial TPP transporter (MTPPT; product of the SLC25A19 gene).

Tilmicosin is a macrolide antibiotic was prepared by chemical modifications of desmycosin, and is used in veterinary. It is recommended for treatment and prevention of pneumonia in cattle, sheep and pigs, associated with Pasteurella haemolytica, P. multocida, Actinobacillus pleuropneumoniae, mycoplasma species and other microorganisms found sensitive to this compound. Tilmicosin belongs to 16-membered ring group of class macrolides. The antimicrobial mechanism seems to be the same for all of the macrolides. They interfere with protein synthesis by reversibly binding to the 50S subunit of the ribosome. They appear to bind at the donor site, thus preventing the translocation necessary to keep the peptide chain growing. The effect is essentially confined to rapidly dividing bacteria and mycoplasmas. Macrolides are regarded as being bacteriostatic but demonstrate bactericidal activity at high concentrations.

Narasin is a polyether carboxylic ionophore agent that is authorised in Europe according to Commission Regulation No (EC) 1464/2004 as a coccidiostat for use in chickens for fattening with a maximum content of the active substance in feed of 70 mg/kg and a withdrawal period of one day. Narasin is the active ingredient in Monteban, a premix that is incorporated into chicken feed. Narasin is already approved for continuous oral use as Monteban (NADA 118-980) in chicken feed for the prevention of coccidiosis at doses up to 80 mg narasin/kg feed. Narasin is produced by the fermentation of a strain of Streptomyces aureofaciens.The biological activity of narasin is based on its ability to form lipid soluble and dynamically reversible complexes with cations, preferably monovalent cations such as alkaline K+, Na+ and Rb+: Narasin functions as a carrier of these ions, mediating an electrically neutral exchangediffusion type of ion transport across the membranes. The resultant changes in transmembrane ion gradients and electrical potentials produce critical effects on cellular function and metabolism of coccidia. Narasin is effective against sporozoites and early and late asexual stages of coccidia in broilers caused by Eimeria acervulina, E. brunetti, E. maxima, E. mivati, E. necatrix and E. tenella. Narasin also is used for prevention of necrotic enteritis in broiler chicken. Narasin was identified and characterized as a novel agent that inhibits DENV replication in vitro through non-cytotoxic mechanisms, thus indicating its potential to be further developed as a therapeutic anti-DENV agent.

Tiamulin is a diterpene antimicrobial with a pleuromutilin chemical structure similar to that of valnemulin. The activity of tiamulin is largely confined to gram-positive micro-organisms and mycoplasma. Tiamulin acts by inhibiting protein synthesis at the ribosomal level. In veterinary medicine, tiamulin is used for treatment and prophylaxis of dysentery, pneumonia and mycoplasmal infections in pigs and poultry. Tiamulin is available as a 2, 10 or 20% premix for pigs and poultry, a 12.5% solution or 45% water soluble powder for addition to drinking water for pigs and poultry, or a 10% injectable formulation for pigs. Tiamulin inhibits protein synthesis by targeting the 50S bacterial ribosomal subunit and binding to peptidyl transferase, the enzyme responsible for forming peptide bonds between amino acids.

Oxfendazole is a broad spectrum benzimidazole anthelmintic. Oxfendazole has broad-spectrum activity against inhibited larval stages of gastrointestinal roundworms, tapeworms, and lungworms in many animal species at doses between 4.5–10 mg/kg.