This post gives a basic description of the method and materials I use to run modified McMaster fecal egg counts on samples collected from my bison herd. A description of why people run these test and how I collect the samples can be found in my previous blog post.
Most of the items I use to run my modified McMaster egg counts. Not pictured are the samples of bison poop, latex gloves, and paper cups used to hold the samples. Yes, I realize I misspelled "flotation" on this graphic, but I'm not going to redo it.
To conduct a modified McMaster egg count on a sample of bison poop I first use the scale to measure out 2 grams of the sample into a paper cup. I then use a veterinary syringe to add 28 mL of flotation solution to the cup and allow the poop to dissolve into the solution. There are recipes you can find on the Internet for making your own flotation solution, but I feel that the commercially available solutions are preferable because they offer greater consistency between batches of solution. Once the poop has dissolved into the solution the mixture is then poured through a piece of cheesecloth into a second paper cup.
A closeup photograph of my McMaster microscope slide. The slide consists of two separate chambers with grid markings that help guide you while you are counting eggs.
As soon as the liquid has drained through the cloth a pipette is used to transfer a portion of it to the McMaster slide, which is then allowed to sit for about five minutes. During this wait period the eggs, which are less dense than the flotation solution, will float up to the top of the slide chambers while most of the other fecal particles sink to the bottom. At this point the slide is ready for the microscope.
The microscope I purchased for these analyses is the Celestron Model # 44104 Advanced Microscope. This microscope comes with a 4x, 10x, and 40x objective lenses (I only use the 4x and 10x for counting eggs) and 10x and 12.5x eyepieces. To view the slide through the microscope I've opted to replace the eyepieces that came with the microscope with a Celestron Model # 44421 Digital Microscope Imager, which I plug into a USB port on my computer. By using this imager in conjunction with a media player, such as VLC, I am able to view the microscope slide on my computer screen rather than having to squint through the microscope eyepiece. This digital imager has the added benefit of allowing me to capture photographs or videos of what I am seeing (see above video).
One of the photographs I captured from sample four. This sample had the largest number of eggs I've seen yet.
The basic procedure in the modified McMaster technique is to count the parasite eggs you can see within the grid markings of a chamber. When I am using a 4x microscope objective, the eggs are large enough to clearly identify as I scan up and down the grid columns by moving the microscope's mechanical stage.
A photograph of the fecal egg count results from five samples I tested yesterday.
Once all the eggs visible within the grid markings of one chamber are counted and recorded, the same procedure is done with the second chamber. The egg counts for each chamber are then added together and multiplied by 50 to give the estimated number of Eggs Per Gram (EPG). Some time in the next few weeks I will treat the bison with an anthelmintic and then run another egg count to see if the anthelmintic is working.
