Sheep Deworming: FAMACHA, Fecal Egg Counts, and Refugia

Author: Elliott Garber, DVM

Modern sheep deworming is not about drenching the whole flock on a calendar. It is about treating only the animals that need it, keeping a reservoir of drug-susceptible worms alive on purpose, and slowing the resistance that has already broken most dewormers. The tools that make this work are FAMACHA eyelid scoring, fecal egg counts, and refugia, and the single most damaging parasite you are managing in most flocks is the barber pole worm.

Meet the barber pole worm

Most of the parasite trouble in a sheep flock in the United States traces back to one worm. Haemonchus contortus, the barber pole worm, lives in the abomasum (the true stomach) and feeds on blood. It gets its name from the way the white ovary of the female twists around her blood-filled gut like a red-and-white striped pole.

The damage is exactly what you would expect from a blood feeder: anemia. Each worm draws a tiny amount of blood, but a heavily infected sheep can carry thousands of them. The American Consortium for Small Ruminant Parasite Control (ACSRPC) notes that a single sheep can lose a meaningful volume of blood per day to a large worm burden, which is why a lamb can look fine one week and be down the next.

The classic signs are pale mucous membranes (check the gums and the inner lower eyelid) and “bottle jaw,” a soft, fluid swelling under the jaw caused by low blood protein. You may also see weakness, exercise intolerance, poor growth, and in severe cases, sudden death. Because Haemonchus is a blood feeder rather than a scour-causing worm, heavy infections often do not produce diarrhea, so waiting for loose manure as your trigger will miss it.

Barber pole worm thrives in warm, wet conditions. In much of the country the heaviest challenge comes in late spring through summer, and larvae can overwinter on pasture or inside the sheep. Ewes also experience a periparturient egg rise around lambing, when their immunity dips and they shed far more eggs onto the pasture their lambs will graze.

FAMACHA: treat the animal, not the calendar

FAMACHA is a simple, powerful way to decide which sheep actually need deworming. You pull down the lower eyelid and compare the color of the conjunctiva against a laminated card. The FAMACHA card is scored 1 to 5: a score of 1 is a deep red membrane (healthy, well oxygenated blood), and a score of 5 is nearly white (severe, life-threatening anemia). Scores 2 through 4 fall in between.

Because the card measures anemia, it is specific to the barber pole worm and other blood feeders. It does not detect the scour worms (like Trichostrongylus or Teladorsagia) that cause diarrhea and poor growth without much blood loss. FAMACHA is a Haemonchus tool, and in most flocks that is the worm doing the most harm.

The rule of thumb from extension programs is straightforward: animals scoring 1 or 2 are generally left untreated, while animals scoring 3, 4, or 5 are dewormed, with 4s and 5s treated as more urgent. Your exact cutoff should be set with your veterinarian, because a heavily challenged flock, thin animals, or late-gestation ewes may warrant treating some 3s that you would otherwise leave.

A few things make FAMACHA work in the real world:

• You need a genuine FAMACHA card, and the ACSRPC requires training (in person or online) to obtain one, because eyelid color is easy to misread without calibration.
• Score in good natural light, and check the animal’s own history: a sheep that keeps scoring 4 or 5 is not just wormy, it is genetically susceptible and a candidate for culling.
• Pair FAMACHA with the Five Point Check, which adds body condition, dag score (manure staining), nasal discharge, and bottle jaw so you catch the scour worms that FAMACHA alone cannot.

FAMACHA is not a substitute for veterinary care. A severely anemic sheep (score 5) is an emergency that may need more than a drench, so loop in your vet rather than deworming and hoping.

Fecal egg counts and knowing what still works

FAMACHA tells you which animal needs help today. A fecal egg count (FEC) tells you what is happening across the flock and whether your dewormer is still doing anything.

A fecal egg count reports eggs per gram (epg) of manure. It is not a perfect proxy for worm burden, because egg shedding varies, but it is the best practical window into parasite pressure. High counts in a group flag that pasture contamination is climbing. Counts also help you identify low-shedding animals worth keeping and high-shedding animals worth culling, which is one of the most durable long-term controls you have.

The most important test in the age of resistance is the fecal egg count reduction test (FECRT). You collect a sample, deworm, and then re-sample the same animals 7 to 14 days later. According to University of Rhode Island extension guidance, an effective dewormer should cut the egg count by about 95 percent or more; reductions of 90 to 95 percent are suspicious, and low reductions, especially below 50 percent, signal serious resistance to that drug on your farm. A DrenchRite larval development assay can screen several drug classes at once from a pooled sample. Run these tests with your vet so you are not spending money on a drench your worms have already learned to survive.

Resistance and refugia: why you should not deworm the whole flock

For decades the advice was to drench every animal on a schedule. We now know that approach is what created widespread dewormer resistance. Every time you treat, the worms that survive are the ones carrying resistance genes, and if you treat everything, those survivors become the entire next generation. Resistance to all three major drug classes has been documented in sheep flocks worldwide.

The concept that fixes this is refugia. Refugia is the portion of the worm population that is not exposed to the drug: the larvae out on pasture, plus the worms living inside the animals you deliberately choose not to treat. Those untreated worms stay drug-susceptible, and when they breed with any survivors, they dilute the resistance genes and keep your dewormers working longer. The FDA now promotes refugia-based control across grazing species for exactly this reason.

In practice, this is why FAMACHA and selective treatment matter so much. By treating only the anemic animals and leaving your healthiest sheep (the 1s and 2s) untreated, you are preserving refugia every single time you work the flock. Deworming everything, or deworming and then immediately moving to clean pasture, does the opposite: it wipes out the susceptible worms and hands the clean field to the resistant ones. Your veterinarian can help you set a refugia strategy that fits your climate and stocking rate.

The three dewormer classes

There are three chemical families of dewormers approved and used in sheep. You do not need doses here (get those from your vet, and never assume a cattle or horse label applies to sheep), but you should know the categories because rotation and combinations are built around them:

• Benzimidazoles (the “white drenches,” including fenbendazole and albendazole). Broad spectrum, but resistance is common in Haemonchus.
• Imidazothiazoles and tetrahydropyrimidines (the “yellow drenches,” including levamisole and morantel/pyrantel). A different mode of action, often still effective where benzimidazole resistance has developed.
• Macrocyclic lactones (the “clear drenches,” including ivermectin and moxidectin). Highly effective historically, but resistance is now widespread.

These families are summarized well by Ohio State University extension. Because a worm population can be resistant to one class and still susceptible to another, your FECRT results should drive which class you reach for. Some programs use combination treatments (giving effective drugs from different classes together) to hit the surviving worms harder, but that is a strategy to design with your veterinarian, not a default. Always dose to the heaviest animal in a treatment group, use the correct oral drenching technique for sheep, and observe the withdrawal period before an animal enters the food chain.

Integrated control: the parts that are not a drench

Dewormers are a shrinking resource, so the durable flock is the one that leans on management. The most useful non-chemical tools:

• Grazing management. Barber pole larvae live in the bottom couple of inches of the sward, so grazing taller and not forcing sheep to graze low reduces intake. Resting and rotating pastures, avoiding overstocking, and grazing lambs on the cleanest fields all cut the challenge. Multi-species or alternate grazing with cattle or horses can help, since they do not share this worm.
• Nutrition. Well-fed sheep mount a better immune response. Extension research shows that ewes on higher-protein diets in late gestation shed fewer eggs, which protects the lambs grazing behind them. Keep body condition, energy, protein, and trace minerals on target, and see our sheep minerals guide and sheep feeding guide.
• Genetics and culling. Resistance to worms is heritable. The ewe or ram that repeatedly needs deworming while penmates stay healthy is passing that susceptibility on. Culling your chronic FAMACHA 4s and 5s, and selecting rams from low-egg-count lines, quietly rebuilds a hardier flock over a few seasons.
• Focus on the vulnerable classes. Lambs, and ewes around lambing, carry the most risk. Time your monitoring to the warm, wet season and to that periparturient egg rise.

Because barber pole worm is a whole-farm, whole-season problem, records are what turn all of this from guesswork into a plan.

Keep records so the pattern is visible

Selective deworming only works if you can see who was treated, with what, and how they scored over time. A sheep that scored a 4 in June and a 4 again in August is telling you something a single visit never could.

On Creatures you can keep each animal’s health and medical records in one place, so FAMACHA scores, fecal egg counts, and each drench (drug class and date) live on the animal’s profile instead of scattered notebooks. Adding a record takes a moment, and the profile tabs keep treatment history, weights, and body condition together. You can also set reminders for upcoming care so a monitoring pass in peak worm season does not slip. If you have not started yet, here is how to add an animal, and you can browse the whole sheep species hub for related care. Naming a new lamb? The sheep name generator is there for the fun part.

Frequently asked questions

How often should I deworm my sheep?

There is no fixed interval, and that is the point. Deworm the individual animals that need it based on FAMACHA scores, fecal egg counts, and clinical signs, most heavily during warm, wet weather and around lambing. Routine whole-flock deworming on a calendar is the practice that drives resistance.

Can I use FAMACHA on its own?

FAMACHA is excellent for the barber pole worm, but it only detects anemia, so it misses the scour worms that cause diarrhea and poor growth without heavy blood loss. Pair it with the Five Point Check (body condition, dag score, nasal discharge, and bottle jaw) and periodic fecal egg counts.

What is refugia in plain terms?

Refugia is the group of worms you leave alone: larvae on the pasture plus the worms inside the healthy sheep you choose not to treat. Those worms stay susceptible to dewormers and breed with any survivors, diluting resistance genes and keeping your drugs effective longer.

My whole flock looks wormy. Should I just deworm everyone?

Talk to your veterinarian first. A flock-wide problem usually points to pasture contamination or a dewormer that no longer works, and blanket-treating can make resistance worse. A fecal egg count reduction test will show which drug class still works before you spend money treating everything.

Is bottle jaw an emergency?

Bottle jaw signals significant blood-protein loss and severe parasitism, and a sheep that anemic can go downhill fast. Treat it as urgent and call your veterinarian rather than relying on a drench alone.

Do this next on Creatures

Whether you are dialing in day-to-day care, planning your lambing season, or shopping for your next sheep, Creatures is the records, marketplace, and directory layer to do it in one place.