Management
It is impossible to remove coccidial oocytes from a farm environment. Hence, control should focus on producing environmental conditions that substantially reduce the number of contaminating oocysts.
It is advisable, with good management, to allow some exposure to coccidia so as develop immunity in birds. Although preventive measures, including isolation and disinfection, can be important, these are unlikely to enable complete control.
Litter
Keeping litter dry, but not dusty, can assist in minimising oocyst sporulation. The location of watering facilities in particular can be critical in the control of litter dampness. Furthermore, since older animals may produce very large numbers of oocytes that may be lethal when ingested by young chicks, it is best to keep age groups separate.
Disinfection
Coccidia oocysts are able to withstand disinfection, although they are killed by noxious gases such as ammonia and methyl bromide.
Older recommendations stress sanitation and disinfection to control outbreaks. These are no longer considered valid as:
Resting pasture
Resting of pasture is recommended by the Soil Association, so as to avoid the build up of contamination in soil. Although the oocysts are temperature sensitive, it is possible for oocysts to survive outside during winter, and they have been known to survive for up to two years (Sainsbury, 1984). In deep litter systems, the combination of dryness, ammonia and bacterial decomposition will result in the destruction of oocysts within 2 weeks of their expulsion in faeces.
Great care should be taken when transferring birds from cages to floors, as coccidiosis is almost bound to occur. This process is unlikely to be a problem on organic farms, as such birds would not meet organic criteria.
Prophylactic measures
Some producers prefer not to use prophylactic treatments, and to treat animals therapeutically when signs of infection occur. Such a strategy does allow the development of natural immunity, but requires high levels of management and vigilance to avoid serious outbreaks.
Prophylactic treatments are available, either in the form of a vaccine administered in water during the first two weeks, or the incorporation of an in-feed coccidiostat. Both UKROFS and Soil Association standards permit the use of in-feed coccidiostats, and vaccines and amprolium in water supplies.
Vaccines
The use of vaccines, such as ParacoxTM, has been shown to be effective (Shirley et al, 1995; Williams, 1998 and Williams et al., 1999), and their use allows organic producers much more flexibility in the control of coccidiosis.
Vaccination is permitted under Soil Association standards. Vaccines are viewed by Lampkin (1997) as being more appropriate to organic poultry systems than anti-coccidial drugs. The vaccine, in the form of standardized doses of sporulated oocysts, is normally administered in water during the first two weeks. Litter conditions must be suitable for oocyst sporulation (i.e. damp but not wet), as the vaccine only introduces the infection.
ParacoxTM is a translucent, viscous suspension of oocysts derived from eight precocious lines of coccidia, and is prepared as a live attenuated oral vaccine for the active immunisation of chickens against Eimeria acervulina, E. brunetti, E. maxima, E. mitis, E. necatrix, E. praecox and E. tenella (NOAH, 1998). It is administered as an oral dose, in drinking water, at a nominal rate of 0.1ml per chicken. A single dose is given between 5 and 9 days of age, inclusive. Since immunity to coccidial infection after vaccination is enhanced by a natural challenge of coccidial oocysts, care should be taken that treated birds do not have access to anti-coccidial substances at this time.
Lunden and Thebo (1999) showed that vaccination with ParacoxTM effectively protected commercially produced broilers from outbreaks of clinical coccidiosis during the rearing period and was at least as effective as a strategy of natural immunisation and drug therapy to prevent losses caused by coccidial infections during the laying period. Waldenstedt et al (1999a) compared immunity levels in groups of vaccinated and unvaccinated birds and found that the number of oocysts shed in vaccinated birds was very low, but during a subsequent challenge with E. maxima and E. tenella the birds' immunity was found to be satisfactory.
In-feed coccidiostats
Coccidiostats are used to suppress clinical infection when immunity has been induced, although these can interfere with the development of immunity. A coccidiostat is included in the feed of young birds in an attempt to control the disease without eliminating the coccidia.
Organic standards, both UKROFS and Soil Association, permit the use of coccidiostats in starter rations, although many producers choose to treat the condition when it arises. In a French survey, chickens reared without anticoccidial agents in their food (poulets biologiques) produced higher and earlier peak oocyst counts in litter than the chickens given medicated food (poulets labels) (Williams et al, 1996).
Most coccidiostat programmes for pullet rearing recommend coccidiostat use at lower levels so as to allow the development of immunity. The administration requires a phased feeding, with coccidiostats being used in the early stages of rearing and withdrawn towards the end of rearing.
Coccidiostats provide a good level of control, but outbreaks, which can be treated with proprietary drugs, still occur.
A regular rotation of coccidiostats is recommended if resistance is to be avoided.
Clopidol (CoydenTM), Diclazuril (ClinacoxTM), Halofuginone Hydrobromide (StenorolTM), Lasalocid Sodium (AvatecTM), Maduramicin Ammonium (CygroTM), Monensin (EcoxTM, ElancobanTM), Narasin (MontebanTM), Nicarbazin (CarbigranTM, CycarbTM, NicarmixTM, NicrazinTM), Robenidine Hydrochloride (CycostatTM), Salinomycin Sodium (SacoxTM, Sal-EcoTM, SalinomixTM) and compound anticoccidial preparations (Amprolmiz-UKTM, LerbekTM) are recommended in-feed prophylaxis of coccidiosis (The Veterinary Formulary, 1998). All of these carry restrictions relating to the age of treatment or the administration to laying hens.
Of the common anticoccidials, only diclurazil has been shown to have any residual anti-coccidial activity (McDougald and Seibert, 1998). Resistance to anti-coccidial drugs has been demonstrated for most drugs.
Recent research suggests the possibility of using newly discovered enzymes produced by Eimeria species as potential chemotherapeutic targets (Williams, 1999).
Development of immunity
Other methods of control involve allowing the build up of immunity. Immunity to coccidiosis occurs promptly and is often sufficient to overcome moderate infection but is seldom complete. Although older birds may be less susceptible because of earlier exposure, there is no true age immunity. A species-specific immunity can develop, and the degree of this will depend on the extent of exposure. Repeated infection with a small number of oocysts produces greater immunity, and causes less damage, than a single infection with many oocysts.
Birds reared on used litter and receiving no medication have been shown to acquire immunity more rapidly than birds reared on new litter (Chapman, 1999).
Breed resistance
Although selection for disease resistance is not generally considered as a control option, as this is more efficiently achieved using vaccination or coccidiostats, Lampkin (1997) proposes that for organic producers, this might in the future be a preferable option to the use of vaccines. Although some genetic resistance to some strains of Eimeria has been observed in some strains of chicken (Long, 1968), this resistance is only partial, as all of these Eimeria strains can produce lethal levels of oocytes.
Rosenberg (1941) showed that breeds such as the White Leghorn, New Hampshire and Rhode Island Red were less susceptible to infection than others such as the Barred Plymouth Rock. However, Buvanderan and Kulasegaram (1972) found that there was more variation within a single breed than can be demonstrated between breeds. More recently, Nakai (1994), Bumstead et al (1995) and Laan et al (1998) have shown differences between breed lines.
Nutrition
Recent work in Sweden, comparing infection in birds fed on pelleted and whole wheat diets, with and without grit, did not show any differences in the number of oocysts shed or mean intestinal lesion scores associated with coccidiosis (Waldenstedt, 1998 and Waldenstedt et al., 1999b). Although feed preparation does not appear to have any major impact on coccidiosis infection, dietary-induced oxidative stress, as a consequence of feeding certain dietary fats, is an effective deterrent against caecal coccidiosis in chickens (Allen and Danforth, 1998).
Poultry fed maize-based diets have been shown to survive coccidiosis better than those on wheat-based diets, as a combined consequence of higher concentrations of vitamin A and E in maize and higher concentrations of niacin and riboflavin in wheat (Williams, 1992).
Alternative treatments
Preventive homeopathic control programmes are available. For more information on the use of homeopathy, contact a homeopathic veterinarian or homeopathic pharmacy.
There only seems to be very limited success with the use of alternative remedies acceptable under organic standards. Research in Austria compared the use of an alternative prophylactic and therapeutic method, based on homeopathy and phytotherapy, with a diet containing a conventional coccidiostat. Although there were no differences in growth performance, mortality rates and the incidence of coccidiosis detected in faeces were higher in birds receiving the alternative treatment (Zollitsch, 1996).