Appendix A: Egg Counting Technique
Modified McMaster Fecal Egg Count (FEC) Procedure The method described below has a multiplication factor of 25, which makes it useful for identifying high strongyle egg shedders, but less appropriate for the FECRT. For video instructions, view HERE.
Supplies needed: ● Disposable paper cup (Dixie cup) or small container for feces
● Small strainer (household) ● Pipette, eye dropper, or syringe to dispense fecal solution ● Cheese cloth or gauze sponge ● McMaster slide ● Flotation medium (specific gravity > 2.5)
Procedure Steps: 1. Weigh out 4 g of feces in a small container or paper cup.
2. Add 26 mls of flotation medium (to bring the volume up to 30 ml) to the feces. Mix well. a. Note: If you do not have a scale, you can add feces to the 26 ml of solution and when the volume reaches 30 mls, you have added 4 g.
3. Strain through one or two layers of cheesecloth, one layered gauze squares, or tea strainer, mix well.
4. Mix the sample well and then immediately withdraw about 1 ml of the suspension with a pipette or syringe and fill the first counting chamber of the McMaster slide. a. Repeat the process to fill the second chamber. b. Let the slide stand for two to five minutes to allow eggs to float to top. i. If visible air bubbles are present, the chamber should be emptied and refilled.
5. Steps three and four should be done at the same time without letting the sample sit between steps, since eggs are in flotation fluid and will immediately begin to rise to the top of the fluid. You want to be sure to get a representative sample of the mixed solution.
6. Once chambers are filled, step three can be started for the next sample. 7. Once filled, the chambers can set for 60 minutes before counting without causing problems if using sodium nitrate. Longer than this and drying/crystal formation can begin. With sodium chloride, crystal formation occurs much more quickly.
8. Count all eggs inside of grid areas (only count the eggs which have more than half of their area inside the outer lines of the grid) at 100x total magnification (10x ocular lens and 10x objective lens). Focus on the top layer, which contains the very small air bubbles (small black circles). Count both chambers. a. Count strongyle (oval-shaped, about 90 microns long) and ascarid eggs (round, about 80-90 microns long). Tapeworm eggs (D-shaped about 80 microns), if present, should be counted as well. Do not count Strongyloides (oval, about 50 microns long) or Eimeria leuckarti (large brown oocysts of the same size as strongyle eggs) – only notations are made as to the presence of these other parasites.
9. Multiply the number of counted eggs in each category by 25 to achieve the number of eggs per gram (EPG) per egg type.
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