Written by Dr. Balkar Bains
The incidence of coccidiosis in chickens is endemic and while it is not possible to eradicate the disease, steps can be taken to control coccidiosis, particularly with anticoccidials.
Effects of coccidiosis
Infection is confined to the intestine, suppressing feed digestion and nutrient absorption, which in turn impairs growth rate and feed conversion efficacy. Infection may remain subclinical, where chickens show no clinical signs or overwhelming infection that may cause significant mortality. The economic cost of coccidiosis incidence remains a serious concern to the poultry industry.
Improved housing and husbandry conditions alone are not adequate to alleviate economic stress due to coccidiosis in poultry flocks. The use of anticoccidial drugs in feed is an additional resource to contain coccidian infections. Prolonged addition of anticoccidial drugs in feed may lead to the emergence of resistant strains and that may develop cross-resistance to other similar anticoccidial drugs.
Several approved anticoccidial drugs are available and remain a major tool for the treatment and control of coccidiosis. Future improvements in husbandry and housing will most likely continue but there is no guarantee new anticoccidial drugs will be developed.
Broilers and Coccidiosis
Broiler chickens at day one have no protective immunity, and remain susceptible to coccidial infection over the broilers’ short growing cycle. Infection starts with a few chickens, and spreads rapidly to others. High bird density, litter on the broiler house floor and the surrounding environment favours oocyst viability and propagation of the feacal oral coccidia cycle.
In cases where anticoccidial resistant strains have emerged, clinical signs of coccidiosis and mortality will most likely be seen from three weeks of age onwards. In all such cases, treatment via water medication and immediate rotation of the feed based anticoccidial would be essential.
Anticoccidials to control coccidiosis
Anticoccidials for feed medication are divided into two groups known as chemicals and ionophores. The selection criteria includes mechanism of action, resistance development and dosage range.
Chemical anticoccidials are generally known as coccidiostats since its mechanism of action arrests the development cycle of coccidian multiplication at the intracellular stage. Once resistant strains emerge, it is generally permanent and there is no immune response so the coccidial cycle proceeds uninterrupted.
Ionophores are known as coccidiocidals and are most effective in killing in the lumen of the intestines, having no effect on the intercellular stage of development of coccidia. Thus, ionophores stimulate some immune response and limit or minimize resistance development. Resistance to ionophores in not permanent and loss of any efficacy is regained following a short withdrawal period. There is an approved dosage range of ionophores for addition in broiler feed and a broader safety margin for toxicity.
Anticoccidial Rotation and cross-resistance
The rotational change of one chemical anticoccidials to another chemical is not suggested due to the real possibility of emergence of cross-resistance. To safe guard against resistance development, chemical anticoccidals should be used for short periods only and follow a change to an unrelated chemical anticoccidial.
The ionophore anticoccidials are classed as monovalent and divalent relating to the mechanism of action involving ion transfer to kill coccidian in the lumen of intestines. A rotation of monovalent to divalent anticoccidial is most effective and usually practiced. A rotation to monovalent to monovalent is possible but for short period. The rotational programs are used continuously with one anticoccidial for the entire broiler growing cycle.
As the name suggests this applies to an anticoccidial program in broilers where one anticoccidial used for a set period first is followed by another anticoccidial to the end of the growing cycle. Coccidiosis incidence varies with each strain and therefore a shuttle program is an ideal alternative for effective control. The selection of anticoccidials for a shuttle program is based on efficacy for each stage and strain of the prevalent coccidian. Shuttle programs can include ionophores to ionophores or chemicals to ionophores at an approved dosage in feed.
Combinations of anticoccidials
Anticoccidials can also be used in combination to increase efficacy and minimize resistance. Possible combinations include chemicals and ionophores added at the standard rates of inclusion for each drug. The combination offers two mechanisms of anticoccidial action, one extracellular and the other intracellular.
The growing cycle of pullets is longer than broilers and low flock density may reduce the feacal oral infection cycle. Oocyst build up in pullet houses is slower than in broiler houses and therefore clinical coccidiosis incidence in pullets is observed at a later age. Feed medication with anticoccidial drugs is effective in controlling and preventing the incidence of coccidiosis in pullets. The overall objective is to induce adequate immunity that will prevent coccidiosis among pullets. It can be achieved by both use of vaccines or approved anticoccidial drugs added in feed for a predetermined period , followed by withdrawal prior to laying. Immunity acquired by this process is of short duration and requires continuous boosting. The oral feacal infection cycle will boost immunity to the cocidia strains present in the poultry house litter. The litter management includes maintaining appropriate temperature, oxygen and moisture in the litter for oocysts survival.
Dr Balkar Bains has extensive experience in poultry farming in Australia and throughout Asia from a diagnostic lab and field perspective. With particular focus on optimizing health of broiler and breeder flocks, hatchability and fertility problems in the hatchery, hygiene and food safety issues, and disease prevention and treatment strategies.