MicroscopeSetupI wrote a long time ago about buying the microscope setup for doing sheep fecal floats, to assess parasite load in the herd. Finally, here is a follow-up to say how it’s going. These are really easy to do! The investment in the stuff ends up being around $100. Much of this is just ordinary kitchen supplies.

I follow the instructions on FiasCo Farm’s site; I find them to be very straightforward. My test tube is a little bigger than the one she describes; but I think the most important thing is to just do it the same each time, so that you are comparing apples to apples when evaluating your own animals.

Gridlines

Learning to read the slides is straightforward, after my first few slides, I found I could move through them rapidly, skipping past air bubbles and spotting parasite eggs. I got curious about using the McMaster method, thinking the slides with the grids on them would be very nice for guiding the eye and keeping oriented on where you are in the slide. And this method gives you the advantage of only needing to count eggs in a small square, then you just multiply up to get the average number of eggs per gram in the sample.

But the slides are expensive. So I achieved a similar benefit from just drawing a crappy grid on my plain slides with a red Sharpie pen. Winking smileI did a particularly sloppy job, just to prove the concept to myself, thinking I’d make a proper one if it worked. But this one actually works fine as-is, I just keep washing and re-using it. Eggs and other matter can still be seen with the red lines as a backdrop; and they provide just enough guidance so that I can move the slide along without losing my sense of location and which eggs I’ve already counted.

Slide

The real McMaster slides (or some equivalent) would be necessary for doing NSIP-style fecal egg counts (FECs), so that you could get fairly accurate comparisons between sheep. But the word is that we don’t have a big enough worm burden in our climate to warrant doing FEC measurements in the NSIP. So I’m just doing this for my own information for right now.

Monitoring the Spectrum of Parasite Loads

I think the big advantage is just being able to see the spread of parasite burden in your own flock. I can see about a 20x variation in my sheep. Some of them will maybe only have 10 eggs in the whole slide; whereas some have so many I really can’t count them accurately, but those are in the neighborhood of 200. So, that’s good information to know.

How I will use this information is to know a baseline of what’s a normal range for my sheep. I have some sheep that look fat and healthy with the count of 200, so I don’t worry about those. But if I see a skinny sheep, I can take a fecal count. If he has 10 eggs in the sample, I’ll look elsewhere for the cause of his lack of thrift, knowing that such a small worm burden is not likely the issue. But if he has 100+, then I’ll assume he’s getting to the upper end of the spectrum and is an individual who can’t tolerate it as well, and then I’ll de-worm that individual only. Then I can re-test to see how effective the de-wormer was that I chose.

This saves on de-worming cost and labor, slows down the development of chemical-resistant worms, and keeps the amount of chemicals I’m running through sheep low. It could also facilitate experimenting with more natural forms of parasite deterrent, such as garlic and herbal remedies. I’m also tracking this data in my database, so I could try to take it into account in breeding decisions, steering away from sheep who have both high worm burdens and lack of tolerance to that. Given that I am seeing such a big variation, I believe this might actually be enough data to use in NSIP, if I wanted to start doing more precise counts. Right now I’m mostly still in surveillance mode, just sampling when I have time, and noting what I’m seeing so I get a good baseline of data to start with.

The Hard Parts

PelletsThe main trouble I am having is that I have a hard time telling apart what kinds of eggs I’m seeing. Getting the total count is the most important thing; but if you want to treat, then it helps to know which parasites you’re targeting, so you can choose the best drug.

The other challenge is getting pellet samples straight out of the sheep, so I know which sheep they belong to! Of course you can just choose random samples out of the pasture if you only want to get a general idea of parasite load in the flock. But given that the variance is wide, you’d have to do a lot of random samples to be sure you’re seeing the whole picture. And then you’d still have to treat the whole herd if you thought there was a high parasite load amongst some individuals.

What I’ve been trying to do is carry a yogurt container to the field with me every day, and if I see a sheep poop, then I gather a sample and note which sheep it was. This is easier said than done, though, because when I’m in the pasture to feed, they are not thinking of pooping, they are thinking of eating! So it’s hard to get samples at this time. I’ve noticed that sheep are more likely to defecate just after getting up from a snooze. So if I were really after multiple samples, I’d probably go roust them from a resting period or follow them around when they are quietly grazing.

This makes me admire those who have large flocks who are monitoring FECs- how do they do it? I imagine they must have to pen up their sheep individually in clean jugs, wait for them each to go, then carefully collect and label samples for processing; so that they can compare most or all their sheep in a similar timeframe.

FEC Class

I took a class on the subject at the last Country Living Expo, taught by Dr. Tim Cuchna from Northwest Veterinary Clinic in Stanwood. He had a slide with pictures of all the different eggs, so you could compare them appearance- and scale-wise. But he didn’t include this slide in his handouts, darn! He did include a text list of parasites commonly seen in our area, listed out by host species, and key indicators (size, shell thickness, egg shape, and whether or not the eggs have “caps” on the ends).  So that should be a helpful guide.

A student in the class had brought a book she uses, I think it was Veterinary Parasitology: Reference Manual. It looked like a good reference to have on hand. Dr. Cuchna recommended that book, and also Veterinary Clinical Parasitology.

The best part of the class, for me, was that we got to bring our own samples and have the Dr. Cuchna look at them. There was a funny worm-like thing that turns up often in my slides, and I was struggling to know whether or not it was a version of lungworm (lungworm is apparently one of the few parasites which will appear in the worm state in the feces, rather than the egg state). It is an odd, hammerheaded thing with a pointy tail, and an internal body structure that makes it look a lot different from plant material. But it didn’t look exactly like lungworm pictures I could find online, just similar. Luckily, I had one example of these turn up in the sample I brought, so I could show him. Dr. Cuchna didn’t think it was a lungworm, he said worms in a sample have a clearly identifiable mouthpiece, which this didn’t.

Dr. Cuchna confirmed what I was thinking: that an animal that’s doing poorly and has an egg count of 100-200 eggs under the entire coverslip, it probably needs treatment. If the animal is doing fine health-wise, then don’t treat, because that just leads to chemical resistant worms more quickly. He also mentioned that when treating for coccidia, ideally you should dose for fifteen days straight (at a minimum, at least seven). Coccidia apparently burrow into the intestine for up to seven days, so you’ll miss those if you only treat once or for a few days, and the infestation will re-emerge.

Microscope Selection Advice

Dr. Cuchna had some advice on buying microscopes, and after using one, I have to agree with him. The microscope I have is a very modest model made for students, and it works just fine. If you only have a few sheep, it’s hard to justify spending over $100 on the microscope. But, if you do have quite a few animals, and anticipate doing a lot of samples, it may be worth considering something a little nicer. Tube

He had four suggested features which make a microscope much easier to use if you’re using it often.

1. Get a mechanical stage, rather than a fixed stage. The stage is the “table” area upon which you set the slide. If it’s not moveable, then you are forced to move the slide around on the stage. It requires fine motor skills, and it’s very annoying if your hand is unsteady or slips, and you lose track of where you are in the slide. I often look at my slides while sitting on the couch, with the microscope on the coffee table; and if a person or dog sits down on the couch, the jiggling messes me up every time! Mechanical stages allow you to clamp the slide down so it sits still on the stage, and then you use knobs to precisely move the stage around under the eyepiece.

2. Get an adjustable light source. Dr. Cuchna felt that the ability to adjust the contrast can help you differentiate difficult-to-see structures in different “layers” of the slide, and very tiny coccidia eggs.

3. Get one that has the coarse and fine focus adjustment knobs together. Some microscopes have them separated, and it’s hard to move your hand between them without taking your eye off the slide. If the knobs are together on the same rod assembly, one big and one small one, your hand can find them both more easily without having to look. My microscope only has one adjustment knob, so it is truly the budget model.

4. Get one with a binocular eyepiece, rather than a single eyepiece. I think this one is most important- I sure find that my eyes get tired looking through the single eyepiece. It must be that making each eyeball focus differently is just a recipe for a headache. This definitely limits me to only doing one or two slides at a time, where I think I could tolerate doing them a lot longer if both my eyes were looking at the same thing.

But all that said, I still want to emphasize that the $80 student microscope is plenty adequate for this job. If buying a more expensive one is such a deterrent that it makes you not get one at all, definitely get the inexpensive one! It is a great tool, and the money and time it can save in de-worming makes it pay for itself quickly enough.

Advertisements