Anticoccidial Drugs

“Anticoccidials are most effective when combined with healthy chicks and good management (adequate space, good ventilation and litter management, ready access to feed and clean water)”
-- Janet Schell (Wallenstein Feed & Supply)

Anticoccidial drugs are medications that are usually added to the feed to prevent coccidial infections. These drugs can also be added to the water to treat or limit infections. When used for prevention, these drugs are used in small quantities starting at day of age and used until the specific withdrawal period. In Ontario (CAN) there are fewer anticoccidials available for use in turkeys than chickens and no anticoccidial drugs with approved application for game birds.

“Anticoccidial medications, like all medicated feed ingredients have to be approved for use by Health Canada before they can be sold and used in feed.  Many anticoccidial medications are registered through the CFIA (Canadian Food Inspection Agency) to be used in the feed without a veterinary prescription. The medication supplier has to show supportive data for both the efficacy and the safety of the medication and clearances are typically given with a specified claim, dosage, species and withdrawal if applicable. If an anticoccidial medication does not have this CFIA Medicated Ingredients Brochure clearance or is used in combination with another medication that is not registered to be used together, then a veterinary prescription is required.” 
-- Janet Schell (Wallenstein Feed & Supply)

Anticoccidial drugs can have a coccidiostatic effect (“in-the-gut” development of Eimeria is halted but able to resume after drug withdrawal), coccidiocidal effect (Eimeria are killed during “in-the-gut” development) or both (1).

Several types of anticoccidial drugs are used or have been used in the poultry industry including but not limited to (1, 2, 3):

1)      Ionophore – produced through fermentation (of various bacteria such as Streptomyces and Actinomadura species) and act as a coccidiocide and coccidiostat by affecting parasite membrane function (e.g. monensin, salinomycin sodium, lasalocid sodium, maduramicin ammonium, narasin)

2)      Chemical – synthetic compounds produced by chemical means

a.       Quinolones – have an effect on energy metabolism of the parasite and act as a coccidiocide and coccidiostat (e.g. buquinolate, decoquinate)

b.      Coccidiostatic thiamine analogs – effect on co-factor synthesis for the parasite (e.g. amprolium)

c.       Guanidine derivatives – active against the first-generation schizonts of E. tenella by preventing asexual replication (e.g. robenidine hydrochloride)

d.      Pyridinols – mostly insoluble in water and active against the sporozoite stage allowing sporozoite penetration of intestinal host cells but not parasite development (e.g. clopidol)

e.       Benzeneacetonitrile - mode of action unknown (e.g. diclazuril)

f.       Nicarbasin – mode of action not defined but thought to impact the parasite’s ability to generate energy

g.       Nitrobenzamides – thought to stop asexual replication (e.g. zoalene)

 Health Canada decides if withdrawals are required and this would be determined based on each drug’s metabolism and clearance from tissues (3). 

Click HERE for a flowchart summary of different types of anticoccidial drugs and their effect and mechanism of action towards certain chicken Eimeria species.

Please consult your veterinarian and feed company representative for information specific to the drug being used on your farm.

A limitation of preventative anticoccidial drug use is the rise of drug-resistant Eimeria strains after prolonged use in the field (4). Several strategies have been created to prevent resistance (see examples in the table below). In general, ionophorous drugs trigger less resistance than chemical drugs.   

Summary of commonly employed strategies used to combat the development of drug resistance (5-8).


 Definition and Rationale for Use

Rotation Program

 Definition: Use of a single anticoccidial drug for several successive flocks before changing to an alternative drug for an equal time period.

Rationale: Drugs with different modes of action are used so if resistance to one drug's mode of action is developed the parasite would be susceptible to the second drug's mode of action.

Shuttle Program

 Definition: Alternate the combination of anticoccidial use between different feed periods during the life of the flock (i.e. different drug(s) within the starter feed, the grower feed and, sometimes, the finisher feed as well).

Rationale: Drugs with different modes of action are used so if resistance to one drug's mode of action is developed the parasite would be susceptible to the second drug's mode of action.

Note: A shuttle program can be part of a rotation program.

Step-Down Shuttle Program
(for replacement layer pullets)

 One drug is used at a predetermined level for the starter period, a second drug may be used at an alternate dose for the grower period and either a third drug or the first drug may be used at a reduced level for a further developing period.

Alternating between live vaccination and anticoccidial programs
(Do not use an anticoccidial drug at the SAME TIME with a vaccinated flock)

 Live coccidiosis vaccines are rotated into a single anticoccidial or shuttle program for one or two flocks to ‘rest’ the anticoccidial program. Most, if not all, vaccine strains of coccidian are drug-sensitive and therefore the poultry house will be seeded with drug-sensitive parasites that will interbreed with any existing coccidia that may have begun to develop reduced drug sensitivity. This approach can greatly extend the useful life of anticoccidials (particularly ionophores) in the field.


1. Chapman, H.D. Anticoccidial drugs and their effects upon the development of immunity to Eimeria infections in poultry. Avian pathology 28:521-535. 1999.

2. Chapman, H.D., T.K. Jeffers, and R.B. Williams. Forty years of monensin for the control of coccidiosis in poultry. Poultry Science 89:1788-1801. 2010.

3. Compendium of Veterinary Products

4. Abbas, R.Z., Z. Iqbal, D. Blake, M.N. Khan, and M.K. Saleemi. Anticoccidial drug resistance in fowl coccidia: the state of play revisited. World's Poultry Science Journal 67:337-350. 2011.

5. Williams, R.B. A compartmentalised model for the estimation of the cost of coccidiosis in the world's chicken production industry. International Journal of Parasitology 29:1209-1229. 1999.

6. Kitandu, A., and R. Juranova. Progress in control measures for chicken coccidiosis. Acta Vet Brno 75:265-276. 2006.

7. Chapman, H.D., T.E. Cherry, H.D. Danforth, G. Richards, M.W. Shirley, and R.B. Williams. Sustainable coccidiosis control in poultry production: the role of live vaccines.International Journal of Parasitology  32. 2002.

8. Reid, W.M., E.M. Taylor, and J. Johnson. A technique for demonstration of coccidiostatic activity of anticoccidial agents. Transactions of the American Microscopical Society 88:148-159. 1969.