Combating Sheep Flock Parasites – Part 2, by Mike V.

(Continued from Part 1. This concludes the article.)

The test is performed with the freshest stool you can get. You can corral the animal, get your gloves on and get in the rectum to get some pellets out, or any number of less stressful ways to get your sample. I just walk into the field and walk behind the sheep or lamb I want a sample from. They routinely walk away and I follow them until they get a little antsy and they will give you what you need in short order. You are not trying to spook them, just be a little annoying so they stay at the slow halting walk so you can spot the pellets and pick them up. You will need two grams (probably two pellets in an adult and four in a lamb) of stool which you place into the 50cc tube. Add 30cc of flotation fluid and then break up the pellets in the fluid to make a slurry. I do this with a flat screwdriver. Technically you are supposed to use 28cc but the line on the tube is at thirty. Let it sit for 5-10 minutes. You will need to strain the slurry into another clean test tube and will need to press the solids within the strainer to drain your effluent through. I have been using the same disposable #10 scalpel blade for the past 5 years. You can now use your pipette to suck up some of the slurry and place it onto the chambers on the slide. I squeeze and eject the contents of the slurry in the pipette ten times before placing on the slide. This mixes the slurry in the tube. Why ten? No good reason. I just do it the same way every time with every test.

The same can be said for 28cc vs. 30cc of flotation fluid, how you break up the pellets, time that you wait before you strain. Do it the same way every time. Apples to apples as they say.
The slides are unique in that they have an elevated cover slip which allows for effluent that you created to stay within the space on the slide via surface tension. You place the pipette at the opening and fill the chamber completely. If you make a mistake or blow in an air bubble, just wash the slide and try again. You have 30cc of slurry and you are only putting about 1cc into each chamber so you have plenty. Lay the slides down and wait about 10-15 minutes which will allow your eggs to float to the upper glass of the chamber while the debris sinks to the bottom. That’s where the specific gravity comes in. The eggs have a specific gravity of around 1.2 and debris at 1.3+.

After the allotted time you can place the slide under 10x magnification, which on my scope is the medium lens. You likely cannot use the high power lens since the slide is way too tall and will crack if you try. The McMaster slide has a grid drawn on the top piece of glass which is what you will focus on. Then it is all a matter of moving the slide to examine each piece of the grid keeping track of the number and types of eggs within the grids. There are two sets of grids per slide and both need to be examined for the correct count. Multiply your egg count by 50 and that is your egg count per gram of stool.

There are some resources on the Internet that include pictures of the common parasite eggs you will find. There are also sites that can provide pictures for debris as well as microscopic pollen. If you have a friendly veterinarian, they may loan you one of their books to photocopy the appropriate pages so you kind of know what you are looking at. Even though we are focusing on haemonchus, there are multiple other pathogenic worms that could be the cause of the problem.

The use of fecal egg counts can also be used for a fecal egg count reduction test as well as determining which animals are more resistant to the worms and shed the least eggs. In my particular case, the ewes that I purchased had a significant count of worms, mostly strongiloids. The ewes were pretty tolerant with a Famacha about 3 but the llama had never seen this worm before and became pretty sick. In a matter of days he went from fine to down with partial blindness. I wormed him with the medicine that the lady who sold me the ewes told me to use and he marginally improved over the following months. That sickness is a post in itself. I started doing my own testing at that point and found that the medicine I was using did not drop the counts significantly.

The fecal egg count reduction test is used to determine whether your antihelmintic is effective or if the parasites are resistant. This particular test uses sugar for flotation and a 90% cutoff. Other sources use a less stringent cutoff in the 50-60% range. You’re basically running egg counts at two-week intervals pre and post dosing. I used my ewes and their offspring as the subjects for the test and went through every class of antihelmintic in the United States over the next few months. The worms in these animals were resistant to all classes except for levamisole and even that had an effectiveness of only 75%. You need to weigh the animal every time you dose levamisole since it has a small margin of safety.

Over the years with repeated testing seasonally you can track when your worms come out of hypobiosis with fecal egg counts and also which animals are tolerant by using the FAMACHA test. If you have to do this many tests you can see how doing it yourself is worth your money. It is also worth your time since you do not have to drop everything you are doing to take stool to the vet and wait for the answer. You can perform your testing while you are completing other activities. It would probably be best to not get sheep that have resistant worms.

Most studies published on the Internet by University sources do not suggest treating by the egg counts but by symptomatic animals. There are sources which state counts in the 2500 eggs/gram range warrant treatment and counts of 1000 eggs/gram in the lactating female should be treated. What if your animal is not thriving and is more anemic than usual and has a count of 500? Common sense says treat but just to be sure I called the veterinarian and he confirmed that course of action. In actuality, every call I have had with the vet regarding my ruminants starts with a set of similar questions. What do they look like how are they acting and when did you worm them last? The reason for treatment on only the symptomatic is because of the ability of the worms to become resistant. It took two years for levamisole to go from 75% to 30% effective which is basically useless. Suggested dosing of antihelmintics is typically by weight and with most agents you can use approximate weights since they have a large margin of safety. Except levamisole.

I do not treat by symptoms but by the time of lambing. By using pasture rotation with 6 month intervals between grazing I can keep the counts less than 200 in all of the females until they lamb. Then the counts skyrocket. If the animal is healthy I will check the counts two weeks prior to lambing and then after lambing. If the counts are high prior I will treat and the counts are always high after lambing so they will definitely be treated after. Most years I can get away with treating the ewes once per year and typically have to treat the lambs once during their year of life. Usually this is around the six month mark. We touched on the resistance issues and there are sources of another class of antihelmintic from other countries which are not available in the US.

I could go on but I am sure you are thinking please stop. In summary, FAMACHA testing is a great tool for keeping track of animal health when it comes to anemia. Fecal stool testing is a valuable skill to learn and will save a significant amount of money depending on how many tests you will perform over the years. You can find the animals in your herd which contribute most to the worm issue, determine resistance and keep track of treatment efficacy which can directly influence the management of your flock.

My parents have come to visit and still wonder what we are doing here and when we are coming back. I asked them once to shush and quiet down for a minute. Their reply was “I don’t hear anything”. Exactly.