Monitoring for Success - Oocyst Counting

This process monitors the number of oocysts present in the environment and can provide an estimation of how well the prevention program is working, or if an outbreak is occurring.

Oocyst counting in the field is based on the oocyst per gram of feces measurement. This process requires communication between the farmer and the technician providing the service to properly collect samples and ensure these samples are being analyzed with the right tools. 

Oocyst counting with live vaccine prevention programs - This process is helpful in indirectly determining successful ingestion of vaccine oocysts via assessing the numbers of oocysts being shed at approximately 7 days of age. The parasite life cycle is between 5-7 days from ingestion of an infective oocyst to the start of oocyst shed. Additionally, this process is helpful in indirectly measuring low level oocyst cycling in the barn by assessing oocyst shed on approximately 14, 21, 28, etc. in the farm.

Oocyst counting with anticoccidial prevention programs
- This process is helpful in determining overall oocyst numbers in the barn which would be indicative of a potential coccidiosis challenge. 

Good Practices When Collecting Fecal Samples from the Barn for Oocyst Counting

When collecting fecal samples in the barn, it is important to obtain a sample that is representative of the full barn environment. A small sample obtained from the first few steps or cages into the barn will not provide a good representation of what is happening.

1. Fecal samples should come from fresh feces not mixed with litter or grass or dried fecal matter found on a manure belt. If material other than fecal matter is picked-up it could skew the oocyst count result. If possible, fecal samples should contain both intestinal and cecal droppings.

2. Fecal samples should be collected randomly from all over the barn and should not be from one specific area.

3. Amount of fecal sample collected should be between 60 to 100grams (about 3-5cm or 1-2inches from the bottom of a ziplock bag). Because larger birds produce heavier droppings, be sure to collect samples from all around the house and not from one location only.

4. Clearly label the sample bags with the information requested from the service technician.

FecalSamplepicture

Figure 1. A normal poultry fecal sample demonstrating cecal and intestinal droppings with white urate.

What Happens to that Sample?

The fecal sample is brought to a laboratory and the oocysts are counted using some variation of the McMaster counting chamber technique. Here, oocysts are measured in oocysts per gram of feces.

A description of the McMaster counting chamber technique can be found here: 

Conway, D.P., and E. McKenzie. Poultry coccidiosis: diagnostic and testing procedures. Blackwell Publishing Professional, Ames, IA. 2007.

McMasterChamberpicture

Figure 2. An example of a McMaster chamber (A) that can be used for counting oocysts.  Oocysts in a fecal sample can be viewed at low (B) and high (C) power magnification with background plant material and air bubbles.  At a higher magnification (C) it is easier to view sporulated versus unsporulated oocysts.  Photo credits: A,B - Thank you to Mr. Kobus Van-Heerden; C- Sloss, M.W., Kemp, R.L. and
A. M. Zajac. Veterinary Clinical Parasitology. 6th ed. 1994.)