Part 6 of a six part series on worm control in goats
Doing your own research and fecal egg counts
by Steve Hart
Extension Goat Specialist
The purpose of this article is two-fold, the first is to explain how to do your own fecal egg counts and second to explain how to conduct on-farm research such as determining whether your dewormer (drug or alternative) is working, monitoring the level of parasitism in your herd, determining the effectiveness of your parasite control program is or determining which animals are more resistant to the Barberpole worm.
FAMACHA© is an excellent tool to monitor the level of parasitism (by the Barberpole worm) in your goats and sheep and is much easier than doing fecal egg counts. However, while FAMACHA© is effective for that purpose, fecal egg counts are more appropriate for research and testing purposes.
FAMACHA© cannot tell you anything about the level of infection of worms other than the Barberpole worm such as the Brown stomach worm or the Bankrupt worm (see the first article in this series (March)Since both types of worms lay eggs (but about half as many as the Barberpole worm), the eggs will be in the feces and be observed when doing a fecal egg count.
Fecal egg counts (done by the modified McMaster procedure) enable one to see smaller changes in the level of parasitism (by roundworms). FAMACHA© (or fecal egg counts done by smear or general floatation procedures) can give you some useful information about how well a dewormer is working, but fecal egg counts by the McMaster procedure can give you a clearer picture.
If you are following worm infection every two weeks to learn the pattern on your own farm, FAMACHA© scores are not as sensitive as fecal egg counts. But, fecal egg counts also have their own disadvantage in that it takes at least 3 weeks from the time an infected larvae is consumed until it is lays eggs.
There is a possibility that your goat could consume a large of infective larvae (which consume blood while they are growing into mature egg-laying adults) and have anemia, but few eggs in the feces. Normally, most of the infective larvae are acquired steadily over the grazing season, but one should remember this weakness. Fecal egg counts also require purchase of some equipment, but depending on your resourcefulness, you can be doing fecal egg counts for less than $200.00.
In this article, we cover how to do some basic types of research using your own fecal egg counts. The first one is to test how effective a dewormer (or alternative dewormer) is in killing worms in our animals. This is called a fecal egg count reduction test (FECRT). To do this, we need a group of animals (test group) that we dose with the dewormer or alternative dewormer. We could use two or three test groups to test several dewormers at the same time.
We need to have a minimum of 6 animals in each test group, but ten or twelve animals are is better. The reason for this is that some animals will respond differently to the dewormer; the dewormer may kill 60% of the worms in one animal and 90% in another animal and we want to get an average that represents our herd. Also, sometimes an individual animal can mount a hyperimmune response (also called “self cure”) and go from 5,000 eggs per gram to 400 eggs per gram. This will happen less than 1% of the time, but it does happen. We also want to make sure the animals have significant worms (at least 500 eggs per gram), so we would do fecal egg counts on them ahead of time or select animals with FAMACHA scores of three or four for our test groups.
First, we collect fecal samples from our test group just before treating them with the dewormer (or alternative dewormer). We treat with the dewormer and let the animals run with the rest of the herd and bring them in between 10 and 14 days later. We collect fecal samples from each animal that we gave the dewormer (or alternative dewormer) to for fecal egg counts. The reason for waiting 10 to 14 days is that sometimes worms will only get a “bellyache” from the dewormer, stop laying eggs immediately but if still alive they will resume laying eggs within a week or so.
We then calculate fecal egg count reduction which represents the percentage of worms killed by the dewormer. It is calculated by subtracting the second fecal egg count from the first one and dividing it by the first fecal egg count. This is done for each animal. For example, if we had 1,000 eggs per gram in the fecal sample before deworming and 10-14 days later the fecal sample only had 200 eggs/gram, we would say we had an 80% reduction in fecal egg count calculated as ((1,000-200)/1000) X 100. Average these values for all the animals in the test group. This means that we killed 80% of the worms in the animal (or we would say a FECR of 80%)
If we did not have resistance to the dewormer, we would expect close to a 100% fecal egg count reduction. If we have less than a 95% fecal egg count reduction, it means that we have the beginnings of dewormer resistance. It is evident from our data that we do have a level of dewormer resistance. At this level of dewormer resistance, it will be expected to get worse (kill a lower percentage of worms) fairly quickly (exactly how quickly it gets worse depends on many factors). However, it still can be a useful dewormer until we get down to killing only 50% of the worms.
Very few alternative dewormers will kill 100% of the worms, but if they kill 50-80% of the worms, they can still be useful to keep worm burden down to where the animals can tolerate them. Don’t forget that after you take the second samples from animals and do their fecal egg counts, those with higher fecal egg counts (fecal egg counts requiring deworming will be discussed later) may need dewormed.
A laboratory test that is an alternative to this test is the DrenchRite test, a laboratory test to determine the resistance to several dewormers. Further information can be found at http://www.scsrpc.org/SCSRPC/Files/Files/D'Rite%20Scsrpc11-05.pdf . Basically, fecal samples are collected from several animals and submitted to a laboratory at University of Georgia for a larval development assay. This evaluates the resistance of worms in your herd to all classes of dewormers. The disadvantage is that alternative dewormers cannot be tested and the test costs $395.00.
Some alternative dewormers are claimed to boost the immune system (takes time) and will slowly kill worms or prevent/reduce new infective L3 larvae from becoming established in the digestive tract of the animal. So, we need to make a slight change in how we conduct the on-farm study. The major change will be to have a group of animals that receive no alternative dewormer (often called a control group; we need to see if the dewormer is better than no treatment at all).
The animals in the control group should be similar to those in the test group, including similar levels of fecal egg counts. We need to take fecal egg counts weekly (in both test and control groups) over a month after administering the treatment and compare the test group to the control group. Both groups should be managed as one herd. In this case, we would expect fecal egg counts in the control group to increase (assuming that infective larvae are available to be picked up by the animal). If fecal egg counts in the test group increase similar to the control group, it means our dewormer is not working.
If our dewormer is working, fecal egg counts will increase at a slower rate than for the control group, reducing the need for deworming. The dewormer may actually cause a decrease in fecal egg counts and hold it at a lower level than the control group indicating a very effective dewormer. If you are using an alternative dewormer, you need to also monitor your test and control groups of animals by FAMACHA© to prevent losses from parasitism. You need to have a plan on what you are going to do if you need to deworm. One could choose to use a conventional dewormer, but if one is certified organic, this needs to be planned with your certifying agency. It could involve moving animals to a pasture that has not been grazed in several months (few infective larvae) or moving them onto browse or sericea lespedeza.
Another use of fecal egg counts is to evaluate the parasite resistance (see box) of animals. This may be done to some extent by keeping track of FAMACHA© scores and the number of times that animals are dewormed in a year. This will enable you to cull the animals that are dewormed the most (assumed to be due to low resistance or resilience to Barberpole worm). Fecal egg counts are a more accurate method of determining which animals are resistant to worms.
Some sheep associations are implementing progeny testing for this trait and calculating EPD (expected progeny difference) for fecal egg counts. A Kiko goat association and a Boer goat association are also interested in implementing this program. These associations have a specific protocol which must be followed. What follows is a generic protocol that is usually applied to young animals being selected for replacements.
After weaning and when the animals have recovered from weaning shock, they are all dewormed with an effective dewormer. One should check the fecal egg counts of a few animals a week or two later to make sure that they are zero, or close to zero. The animals are all grazed together for 8 weeks and a fecal sample is taken at the end of 8 weeks for a fecal egg count. It would be advisable to monitor animals with FAMACHA© in case animals get heavily infected. If several animals become 4's in 6 weeks, fecal samples may need to be taken at that time and animals dewormed as necessary. One can then select the animals with lowest fecal egg counts for replacements. This tool is especially important for bucks since they contribute over half of the genetics of the next generation.
Animals may be either resistant to parasites or resilient (tolerant). Resistance is that fewer worms become established in the animal as compared to other animals in the herd. This is thought to be predominantly due to having a stronger immune system which suppresses the worms better, but one study indicates that an animal’s grazing habits (how close they graze to the ground) may be a factor.
Resilience (or tolerance) is that one animal with 1,000 Barberpole worms will show less anemia than the other animals in the herd with 1,000 Barberpole worms. Resilience may be due to a greater ability to make blood as compared to other animals. In this case, a resilient animal would have a lower FAMACHA© score (less anemia) as compared to other animals. However, we can’t tell if an animal with a lower FAMACHA© score is resistant (fewer worms sucking blood) or tolerant (makes blood faster to replace what the Barberpole worm sucks). But if we select for a low FAMACHA© score, we know some of it will be due to greater resistance to the Barberpole worm.
If we select animals for a lower fecal egg count, we are selecting for resistant animals. From studies in Australia and New Zealand indicate that it is better to select resistant animals than resilient animals because resilient animals will be producing more eggs than resistant animals, creating more infective larvae for everyone else in the herd, resilient or not.
Fecal egg counts can be very effective for understanding patterns of infection and where parasite management needs to be changed, or to determine if a change is helping. This is done by randomly selecting a group of animals (six to twelve head) to follow during the warm season (assuming the Barberpole worm is the major parasite in your area). We will follow these same animals throughout the warm season, so it may be useful to mark them with an additional eartag or other mark to enable them to be readily sorted for sampling.
The best way to randomly sample your animals is if you have 100 animals and want to select 10 animals to follow, select every tenth animal that goes through the chute. The first animals to the chute are usually healthier whereas the last animals are less healthy and more prone to worms, so we want to select some of each kind of animal. The time to start will vary for different
Six part series
Worm control in goats
Part 1: Meet the enemy
Part 2. Managing the barber pole worm
Part 3. Integrated parasite management with FAMACHA©
Part 4. Dewormers and dewormer resistance
Part 5. Alternative dewormers: do they work?
Part 6. Doing your own research and fecal egg counts
This six part series on worm control in goats was originally published in The Goat Rancher magazine in 2008.
geographical areas, but one should probably start monitoring animals when daily temperatures are getting into the 70's.
Generally, taking fecal samples every three weeks is adequate to monitor the level of parasitism. It is also useful if one can keep a record of rainfall since moisture is important for eggs to develop into infective larvae. Recording other animal management practices such as which pasture was grazed, when moved, supplemental feed, kidding or lambing, etc. can assist one in interpreting fecal egg count pattern. If fecal egg counts are graphed, one can often observe when the infection level has increased in animals. One has to think back to what happened four to eight weeks prior to the increase in fecal egg counts because it takes three to four weeks from the time your animal picks up infective larvae until those larvae are mature worms, producing eggs.
The second article in this series (published in April) on the biology of the parasite can help in understanding why fecal egg counts increased and some management options to help prevent it next year. Your veterinarian, state sheep/goat extension specialist, parasitologist can help you with interpreting the data as well as suggesting changes in management.
Fecal egg counting procedure
There are many procedures for determining fecal egg counts and many variations of each procedure according to equipment available. There are references to other procedures on the web at the end of the article. The McMaster fecal egg counting procedure is a good technique to monitor parasite level of grazing animals and is commonly used for parasite research. It is the method of choice for producers because of quantitative data and simplicity.
Watch goats drop pellets, collect fresh pellets and record animal numbers. The pellets should still be glossy when collected.
Use patient examination glove, lubricate with water or spit and tease 5-6 pellets out of the rectum.
Store in labeled (with animal name or number) ziplock bags on ice or in refrigerator for up to 7 days before doing fecal egg counts. Do Not Freeze! If fecal samples are not refrigerated, they can start to hatch in several hours at warm temperatures, reducing fecal egg counts. Samples can also be stored in patient examination gloves by closing the open end of the glove with a rubber band and writing numbers on glove with sharpie marking pen.
Principle of Fecal egg counting procedure
Loosen worm eggs trapped between fecal particles and separate eggs by floating them away from fecal particles. Must use proper ratio of feces and solution to get correct eggs/gram.
Choose one of the following flotation solutions.
Add 1 cup water to 1 1/4 cup sugar and mix (easiest to mix, good choice)
34% solution of zinc sulfate (used for footbath)
Saturated Sodium Nitrate solution (28% N, fertilizer)
Saturated solution of salt, rock salt or uniodized salt (requires heating and a lot of stirring)
Can purchase Fecasol or generic fecal float solution for $5-10./gal from vet supply house (requires a prescription from your vet)
Microscope 10X objective 10X wide field (WF) eyepiece, mechanical stage is handy. Can get one for $75.00 EZ Scope Model MEZ 119 (do a web search for MEZ-119 for sources). Many children’s or toy microscopes have a narrow field of view i.e., cannot see lines on both sides of lane of McMaster slide. You can get a used microscope from many places: E-bay, classified ads in newspaper, etc. Your high school science teacher may help you get access to a microscope. Your vet or the doctor’s lab tech may have an old microscope that they can sell you cheap. You can find out who services their microscopes since they may also sell used microscopes. Some friends or relatives may have a microscope from their college days stashed in the attic.
McMaster slide (green). About $20. This slide has a top and bottom with a space between that you put the solution to be counted. It has 2 squares and each square is divided into six columns. The column is the same width that you can see in the eyepiece of the microscope, so you can count up and down the columns.
30 cc syringe
Balance or scale to weigh to 0.1 grams ($20.00 new on Ebay) r three cc. syringe with end cut off
Teaspoon/tongue depressor/popsicle stick/spatula
Fill syringe to exactly 28 cc with floatation solution.
Add 28 cc of solution to salsa dish
If you have a balance, 2.0 g of feces can be weighed out directly into tea strainer. It may be necessary to cut a pellet with a spoon to get 2.0 grams. If you do not have a scale, you can mash fecal pellets into a 3 cc syringe (end cut off) and form a solid column of feces. Push plunger to 2 cc mark and cut off excess feces. Push the 2 cc out into a tea strainer in salsa dish. Two cc of solid packed feces = 2.0 grams.
Use spoon or other tool to crush, mash and break up feces and form a slurry without lumps, will take 2-3 minutes.
Lift tea strainer out of salsa dish and discard residue in it.
Stir solution in salsa dish 8 times and use eyedropper to fill one chamber of slide
Stir solution in salsa dish 8 times and use eyedropper to fill other chamber of slide
Allow slide to sit 5 minutes.
Look at slide under microscope and focus on air bubbles in sample
Move slide on microscope down lane one and up the next lane looking for eggs-oval football looking objects (see picture below)
Can identify tapeworm eggs and coccidia. We are most interested in roundworm eggs, so just count them
Count all eggs in 6 lanes on one square (it may be useful to use a lap counter)
Count all eggs in 6 lanes on the other square and total eggs from both squares
Multiply total by 50 to get eggs per gram
Strongyle = roundworms, includes barberpole worm, bankrupt worm, brown stomach worm, black scour worm
Nematodirus = thread-necked intestinal worm
Trichuris = whip worms
Strongyloides = thread worms
Care of McMaster slide
Wash in dishwashing detergent and water
Sling out excess water and allow to air dry
Roll in paper towel until next use.
Count only roundworm eggs although you may also see eggs of thread worms, whip worms, thread-necked worms and coccidia (see pictures on above referenced web site). Roundworm eggs look like rounded end footballs with a yolk and shell. Coccidia look similar, but are only about ¼ the size of roundworm eggs. The thread-necked worm egg is very, very large. The whip worm egg has a polar plug on each end. Threadworms have what looks to be a baby worm in it rather than a yolk.
It is difficult to interpret what the number of coccidia means. Virtually all sheep and goats will have some coccidia, some more than others. Yes, about 24 hours after an animal gets diarrhea from coccidosis, you will see many, many coccidia when doing a fecal egg count and coccidia numbers will decrease as the animal gets well. But in the first 24 hours that the animal has coccidiosis and diarrhea, there will often be few coccidia in the feces.
Since the damage to the small intestine is reduced by early treatment, do not wait until you see a lot of coccidia in a sample of a goat with diarrhea to treat them. If you think they have coccidiosis (history of stress such as disease, weaning, shipping and have diarrhea), treat them immediately for coccidiosis.
Thread worms are generally not a problem, but sometimes increase in animals with high fecal egg counts. They can be particularly bad in young animals raised in a stall with wet bedding, because these worms can directly penetrate the skin. Now you know another reason for keeping bedding clean. We do not know how to interpret whip worms either. They sometimes increase in animals with high fecal egg counts, but generally do not cause sickness. Thread-necked worms can be a significant problem in cool climates. But, we only count roundworm eggs for our purposes.
Now that you have a fecal egg count (number of roundworm eggs per gram), what does it mean? We can decide if it is high enough that the animal needs to be dewormed. If it is the warm season of the year and the Barberpole worm is the dominant species (ask your vet if in doubt), you need to deworm dry does and bucks when the fecal egg count exceeds 2,000 eggs per gram. For lactating does, yearlings and kids, 1,000 eggs per gram or more is reason to deworm. Fecal egg counts for deworming are similar for sheep. If you have lactating dairy does, those with over 750 eggs per gram will require deworming.
FAMACHA© is a better tool to determine when animals need dewormed and should be used with fecal egg counts to determine if deworming is needed. If it is the cool season time of the year, and the brown stomach worm or bankrupt worm are the predominant species, they lay much fewer eggs than the Barberpole worm and you will need to think about deworming when fecal egg counts are half of the above levels.
However, one should also give consideration to fecal consistency (diarrhea is a major symptom of infection for non-Barberpole worms) and body condition (has the goat lost weight or look wormy like?) in making decisions on the need for deworming. Consult your local vet, state extension sheep/goat specialist or parasitologist for assistance in interpreting fecal egg counts.