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Managing Summer Parasites

managing summer parasites
Sheep pick up parasites from grass blades.


With the sheep on pasture full time now, managing summer parasites becomes top priority on our farm. At this time of year, an over load of intestinal parasites is the primary cause of illness and even death in sheep, often effecting those with a compromised immune system, nursing ewes, or young lambs. I have found that the key to conquering parasites is understanding their life cycle, and monitoring and testing fecal egg counts.

The Life Cycle of Parasites

  • The adult nematodes inside of the digestive tract of the sheep mate and lay eggs.
  • These eggs are passed out of the sheep through their feces.
  • As the feces disintegrate on pasture, the eggs hatch.
  • Feeding on the feces, larvae develop and climb grass blades towards the sun, typically living  on the first 2 inches of the grass blade.
  • Sheep eat grass and ingest the larvae.

Monitoring For Internal Parasites

We monitor our sheep closely for parasites and do fecal egg count tests regularly beginning in May. When observing our sheep, we look for several things:

  • FAMACHA score-Using a FAMACHA card, we determine the color of the mucous membranes around the eyes and gums. Pale or white membranes indicate anemia and possible parasite infestation.
  • Body condition-thin animals or those not gaining weight properly could be compromised by a parasite overload.
  • Condition of feces-sheep with runny stools are always tested. Lush pasture may also cause diarrhea in sheep, but will clear up once their systems adjust to being on pasture.
  • Any signs of lack of thriftiness.

Testing Fecal Egg Samples

We do fecal egg counts on all of our sheep once a month. This is the best way to monitor how well they are handling parasites. Some sheep will be naturally more resistant than others and it is important to know who these sheep are. When testing my entire flock, I will send fecal samples to MidAmerica Agricultural Research for testing. This lab uses the “Modified Wisconsin Sugar Flotation Method” of testing, giving very accurate results.

If I am concerned about just one or two animals, I will run a fecal sample test myself using a Modified McMaster Test. This will let me know if the sheep has a problem and give me an indication of how large a parasite overload.  It is important to note that these two methods of testing give very different test scores. It is essential to understand the scoring procedure in order to know when to treat an animal. With the Wisconsin Sugar Flotation Method, the scoring is as follows:

  • Score of 1-10/low parasite load
  • Score of 11-50/medium parasite load
  • Score of more than 50/high parasite load

I only treat those sheep with a high load, or a score above 50.

The Modified McMaster Test scores much higher numbers as you are extrapolating the  number of eggs/gram in the manure. In interpreting the results, I take into account other factors such as the over health, mucous membrane color, and thriftiness. Typically, I do not treat an animal unless their McMaster Test score is above 350, but I always consult with my vet first. If I am in doubt, and the sheep has a very high egg count, I will then send a sample out to MidAmerica to be tested again.Managing summer parasites

Do-It-Yourself Modified McMaster Test


It is easy to do your own fecal egg counts using the McMaster method. The key to success is to be consistent in your test methods and measuring. You only need a few things to begin doing your own parasite monitoring: a microscope, McMaster slide with a grid, small scale, flotation solution, plastic cups, strainer, small syringe, and a fecal sample.

monitoring parasites

  • Collect your fecal samples and put in zip lock bags labeled with name of sheep.
  • Measure 2 grams of feces and put into cup with 28 grams of flotation solution.
  • Mash the feces, mixing with the solution.
  • Strain the mixture with  a fine sieve or strainer. I use a tea strainer.
mcMaster slide
You can see the grid lines on the slide. You will be counting the number of eggs within the grid lines.
  • Stir the strained solution back and forth 8 times and immediately draw into a 1cc syringe.
  • Using the 1 cc syringe, fill each side of the McMaster slide with the solution. Let the slide sit for 5 minutes to allow the eggs to float to the surface.
  • Put slide under microscope and find the corner of the grid. Begin counting at the top left corner, moving down the column and then up the next and so forth. You only count the eggs within the grid lines.monitor parasites

For more intensive instructions on the McMaster Method of fecal egg testing, visit the University of Rhode Island website.

Do-it-yourself fecal egg tests for managing summer parasites in your flock are simple, and give you lots of useful information about the health of your flock, their resistance to parasites, and the health of your pasture. And who doesn’t enjoy looking at cool stuff under a microscope?! Your veterinarian will appreciate and be impressed by your interest in monitoring the health of your sheep.


2 Responses

  1. thecrazysheeplady

    My vet would probably be NOT happy about me learning to do that as I currently pay them to do them ;-). Took Biscuit and Muffin in for a recheck this a.m. I’ve toyed with learning to do this myself. Thanks for posting this!

    • Kim Goodling

      Ah yes….well my vet is so busy that she loves it when shepherds learn to do some things on their own so she can tend to the bigger issues. It is super easy to learn and so convenient when you just need that peace of mind that all is well.