Guideline for Evaluation of the Efficacy and Safety of Coccidiostats
Guideline No. 24
Last revised: September 1992
The emphasis in this guideline is on simplicity. For a fuller treatment, attention is directed to reports from a Coccidiosis symposium Experimental Parasitology, volume 23, Number 1, August 1970, under the title “Methodology for the development, selection and testing of anti-coccidial drugs for use in controlling coccidiosis”.
Studies cover three types of testing: Battery, floor Pen and Field Trials. All should be under the supervision of a qualified investigator, and battery and floor pen studies particularly should be designed so that the degree of efficacy can be shown to be repeatable through the use of appropriate statistical methodology.
1. Battery Trial
This is usually carried out in the laboratory under controlled conditions using susceptible chickens which are uniform for breed, sex and chickens, when infected, are 2 to 2 1/2 weeks of age. Treatments should be replicated.
Data should be developed for each coccidial species for which claim is made and also on mixed infections of these species.
It is desirable that the test coccidiostats be mixed by the testing laboratory into the basal ration avoiding cross contamination with other coccidiostats.
Usually this short-term trial runs eight days after infection. The infective dose of sporulated oocysts is usually administered two days after medication with coccidiostat has commenced. Individual administration of oocysts directly into the crop of each chicken is recommended.
The test should provide significant responses relating to such factors as: mortality, weight gain, lesion scores (0 to ++++) of chickens which die during the test and of those which are sacrificed at the completion of the test.
Artificial infections of E. tenella and E. necatrix should aim to produce 25 per cent mortality in the controls with smaller percentages for the less virulent species.
Anti-coccidial indices may be used for expressing the efficacy of coccidiostats.
2. Floor Pen Trials
Floor pen trials should be designed to confirm efficacy of the coccidiostat using unmedicated controls against coccidiostat medicated test groups under natural or artificial coccidial exposure.
An example of suitable facilities for such a trial would be an open type shed with deep litter over a well drained concrete floor containing eight to twelve pens on each side of a central passage way, each with a minimum capacity of 100 broiler type chickens. this would allow testing of three potential coccidiostats and a control with four to six replicates suitably randomised for each treatment. A treatment with a reference coccidiostat may be included, if desired.
Coccidial exposure, normally with mixed infections, should be sufficient to produce a clinical effect, but preferably at least 10 to 15 per cent mortality in the unmedicated controls.
Artificial exposure is usually induced when chickens are 2 1/2 to 3 weeks of age.
A floor pen trial will run for about eight weeks, and efficacy can be evaluated by criteria such as:
- Mortality, autopsy and lesion scores on dead chickens.
- Lesion scores on three to five randomly selected chickens from each pen at, say, five to six weeks of age.
- Weight gain and feed conversion ratio.
3. Field Trials
These should be conducted in two or three different climatic areas for the purpose of demonstrating the utility of the anticoccidial agent under commercial conditions.
Commercial facilities normally available for such trials are not ideal for accurate assessment of coccidiostats owing to marked variations in environmental conditions from farm to farm and from shed to shed. The sources of error in field trials are numerous and one should recognize their limitations. such trials are, however, essential to show that the coccidiostat can be efficiently mixed in commercial feed.
Every endeavour should be made to secure uniformity of management and facilities including housing, ventilation, brooding, type and distribution of waterers and feeders. As far as possible the chickens should be uniform in strain, batch and sex. Most sheds take 5,000 to 10,000 birds.
Samples should be kept from every feed delivery for check analysis of levels of coccidiostat to ensure that the commercial feed has been accurately mixed.
The trial should be closely supervised and accurate records kept.
The following housing arrangements have been used (order of preference):
- Two or three sheds of identical size divided into three or more equal pens.
- Four equal sheds for cross-wise comparison of two coccidiostats.
- Two equal sheds with one coccidiostat in each.
- Equally divided shed to test two coccidiostats with provision for some controls on non-medicated feed to be placed in each half in a secure enclosure.
Most field trials depend on natural exposure and replication of treatments and trials is highly desirable.
The following are the usual criteria for evaluation:
- Mortality and autopsy findings.
- Lesion scores at five to six weeks on five randomly selected chickens from each group.
- Average weight at slaughter, feed conversion ratio, and economic performance of each group.
4. Compatibility
Some evidence is desirable on the compatibility of the coccidiostat with various other feed additives. Overseas data should be acceptable.