All goats that spend time grazing on pastures will be infected with parasites. The mature worms (also known as nematodes) deposit eggs in the gastro-intestinal (GI) tract, which are excreted through the manure and onto the pasture environment. Eggs hatch and the larvae lie in wait on the grasses. Goats infect or re-infect themselves as they eat the pasture grass, ingesting the larvae, which mature and lay more eggs, starting the cycle all over again. The majority of parasites have this life cycle both inside and outside of a goat’s GI tract.
|Above: A typical digital scale.|
Below: The sample being strained in a cup.
Parasites are living organisms that will negatively affect the health of all goats to varying degrees. Young goats are particularly susceptible to the parasites as are goats with chronic health problems such as pneumonia or other weakened conditions. The sure-fire way to determine if goats are infected, either modestly or severely, with parasites is to periodically examine manure samples. Even if goat owners or caretakers employ a regular de-worming program, they are encouraged to conduct fecal sampling and testing to determine if the drugs they are using are working and the relative effectiveness on individual goats. The use of a fecal test by itself will not tell the goat owner if the health of their goats is compromised. It is used to help make decisions as to how to manage a de-worming program.
The family of nematodes that is of most concern to goat health are called strongylids. The Barberpole Worm (Haemonchus) and the Brown Stomach Worm (Ostertagia) are two of the most troublesome strongylid nematodes found in many U.S. goat herds. The degree of infection and the number of eggs found in the manure will vary depending on the season of the year.
The McMaster slide being carefully filled with solution. Note the grid lines that will help locate and count eggs under the scope.
A fecal test that is quite popular and fairly easy to do (and learn) is called the Modified McMaster Fecal Egg Counting Test. The McMaster Test utilizes a flotation technique and a special microscope slide. The McMaster slide is unlike a simple microscope slide in that it has two small slotted chambers that allow for a thicker puddle of liquid to be examined. The slide also has grid lines embossed for easier counting of eggs.
A manure sample is mixed with a flotation solution and placed in the chambers of the slide. The eggs will float to the top of the solution where they can be examined under a microscope and counted. Users will need to invest in both a high quality microscope and digital scale along with some chemicals and lab equipment. Interpreting the results of the tests will take some time and practice.
The slide is placed under the scope.
Fresh manure samples are essential for the accuracy of the test. When collecting samples they must have been taken directly from the goat’s colon/rectum by inserting a finger or two into the rectum. A second option for collection is to actually observe the manure "hit the ground" and collect it while it’s still warm and uncontaminated. Fecal samples that have set on the ground for any period of time can become contaminated with soil or feed materials making the sample more difficult to examine and evaluate. Fecal samples can be refrigerated for several days.
When determining the level of severity of parasitic infection in a goat herd it’s highly recommended that goats be sampled individually. A composite sample coming from a number of goats will establish the fact that there are parasites in some of the goats but leaves the question of which ones. The level of severity of an individual goat cannot be determined from a composite sample. As an example, a composite sample from five goats may show significant egg levels but the eggs might only have come from two of the five goats sampled. The use of a dewormer on three of the goats would be unnecessary.
Parasite egg. This is what a typical strongylid egg will look like under the microscope. This is what were looking for on the slide.
The primary function of the McMaster technique is to be able to establish a quantitative egg count from the strongylid family. Identification of individual worm species is not possible unless the examiner has a lot of experience. For the most part strongylid eggs are very similar in appearance and size so it’s very difficult to tell if the sample contains the Barberpole Worm or Brown Stomach Worm. The key to effective use of the McMaster Flotation procedure is recognizing the presence of strongylid eggs since all species of Strongylid are undesirable and potentially harmful to goats. With experience examiners will also be able to identify other eggs such as the coccidia oocysts and tapeworm and whipworm eggs. All of these can be identified on the McMaster flotation slide.
Fecal egg counting should be used as part of a total management program in monitoring and controlling parasite infections in goat herds. Goats must have a minimum of 150 to 200 eggs per gram of manure before treatment with a dewormer. Goats with egg counts that are less than 150 are not seriously enough infected to cause any significant health problems and do not warrant the use of a dewormer. The ultimate goal of regularly counting parasite eggs should be to determine how effective is a deworming program and the drugs that are being used. As noted earlier, all goats that graze pastures will have parasites to some degree. To avoid the over-use of dewormers and the tendency for all dewormers to become ineffective, dewormers must be used judiciously and only on those goats that truly need them. By following up with a second sample 10 to 14 days after the application of a dewormer, goat owners will be able to tell if a particular deworming product is effective in reducing egg counts and parasite infections in their goat herds.
- Microscopes need to have at least a 10X objective to properly evaluate samples. Because of the high level of magnification of a 10X microscope, having a movable stage for viewing the slides will make viewing and counting eggs much easier. Microscopes of this caliber will cost in the range of $500. A digital scale that measures down to a tenth of a gram (.1 gram) is preferable to a scale that measures only in one-gram increments.
- The floatation solution can be either a saturated solution of sodium chloride or magnesium sulfate (Epsom Salts). A commercial solution called Fecasol (sodium nitrate) is available from veterinarians. Users can easily go on line and Google all this information to learn how to make a "saturated solution" of either NaCl or MgSO4 or just purchase the Fecasol. There is also much more information available on the McMaster Flotation procedure.
Modified McMaster Fecal Egg Counting Standard Operating Procedure
Reference: Whitlock, H.V., 1948, Some Modifications of the McMaster Helminth Egg-Counting Technique and Apparatus. Journal of the Council for Scientific and Industrial Research 21, 177-180.
- Paper or plastic cups, at least 5 oz.
- Straining techniquethis can be a tea strainer, unfolded gauze 4" x 4" pads or squares or cheesecloth cut into squares (6" squares preferred)
- Tongue depressor
- Fecal flotation solution (can be Fecasol®, saturated NaCl or saturated Epsom Salts)
- Dispenser bottle for flotation solution
- Transfer pipettes or 1 ml syringe
- Two-chamber McMaster slides (Chalex Corporation, Wallowa, Oregon). Slides with the green grid lines are easier to read.
- KY Jelly – water based
- Gloves – powder free
- Labels (1" x 3")
- Permanent marker
- Compound microscope with internal light source, moveable slide (4X and 10X objectives)
1. Collect 4-5 grams of rectal fecal material using a gloved hand with lubricated fingers.
2. Pull off glove to encase fecal material. Express as much air as possible, twist the wrist portion of the glove and attach the paper label (with farm and animal ID) making sure the label sticks to itself.
3. Label two cups with animal and farm ID.
4. Tare labeled cup and tongue depressor on scale.
5. If manure is pelleted, crush the pellets in the glove. Cut off fingertip of glove containing feces to access fecal pellets making sure to leave label intact.
6. Measure 2 grams of fecal pellets into cup on scale.
7. Using tongue depressor mash any uncrushed fecal pellets against the side of the cup.
8. Dispense 28 ml flotation solution into each cup, mix and let soak for approximately 5 minutes.
9. Continue weighing out samples, mashing pellets, adding solution and mixing until 6-10 samples are set up.
10. Return to the first sample and mix again. Place tea or fabric strainer on top of the cup (make a depression in fabric). Pour the mixture of feces and flotation solution through, pressing out excess fluid with the tongue depressor.
11. Using a transfer pipette or syringe, immediately fill both chambers of the McMaster slide. If large bubbles are present, empty the slide and refill. Even if a large bubble is not actually under the grid, the slide should be refilled. Fill the entire chamber, not just the area under the grid.
12. Set slide aside for at least 5 minutes to allow parasite eggs to float to the surface. Read slides within about an hour of filling the slide. If slides are left too long, fluid evaporates and salt crystals form.
13. Place McMaster slide onto the microscope stage.
14. Bring the green grid lines and black air bubbles on the McMaster slide into focus using the low power (4X) objective. Count all eggs inside of the grid areas using the 10X objective (include eggs on the grid line if greater than 1/2 of egg inside grid) in both chambers.
15. Always start at the same point on the McMaster slide (for example, top left or bottom right). That way, you won’t lose track of whether you have counted both chambers or only one.
16. A separate data sheet should be used for each farm.
17. Count only strongylid eggs (oval shaped, 80-90 microns long). Quantify Nematodirus eggs separately as they can be clearly distinguished but include in the total count for both chambers. Other parasites present should be recorded and may be counted if desired, but numbers are often difficult to interpret.
18. Total egg count: (chamber 1 + chamber 2) * 50 = eggs per gram (EPG).