A Better Way to Drench Sheep With Levamisole: My Mid-Range Mix That Actually Works

Levamisole (Prohibit) is one of the most effective dewormers we still have for sheep, especially against resistant Haemonchus contortus. But anyone who has drenched sheep with it knows the truth: the label dosing options are terrible.

The "concentrated" option is so small that sheep spit it out. The standard "diluted" option is such a massive volume that sheep choke, gag, and fight you the entire time.

Over time, I found a much better middle ground. A mid-range dilution that my sheep swallow reliably, that reduces overdose risk, and that delivers the correct mg/kg dose every single time. It has made levamisole drenching easier, safer, and far more effective on my farm.

Here’s what I learned.

Why the Label Dosages Don’t Work Well in Real Life

1. The concentrated dose (2 mL per 50 lb)

The concentrated mix looks convenient on paper, but in practice it’s a mess:

• Tiny volume

• Easy to spit out

• High overdose risk (levamisole has a narrow margin of safety)

• Hard to measure precisely
  

If a sheep spits out just half a milliliter, you’ve already under-dosed them, and under-dosing is how resistance builds.

2. The "unconcentrated" large-volume dose

This one is even worse. At big bodyweights, you’re talking 100–150 mL orally. No sheep likes having that volume dumped in the corner of their mouth, and honestly, it’s not fair to ask them to swallow that much fluid while fully restrained.

• They gag

• They cough

• They aspirate

• They fight

This volume isn’t practical, and it’s not safe for them.

My Mid-Range Mix: The Goldilocks Formula

After experimenting and doing the math carefully, I settled on a much more manageable formula:

My recipe:

• 13 grams of Prohibit powder, which is 1/4 of a 52 gram package

• 16 ounces of water

My dosage:

• 7.5 mL per 50 lb bodyweight

This delivers the exact therapeutic target of 8 mg/kg, which is the correct levamisole dose for sheep.

No underdosing. No overdosing. No drama.

Why This Mid-Range Dose Works So Well

✔️ The volume is perfect

Too little and they spit it out. Too much and they choke. At 7.5 mL per 50 lb, even a large ram only gets about 30 mL. That’s easy for them to swallow, and it triggers the natural swallowing reflex rather than panic.

✔️ More accurate than the concentrated mix

When you’re dealing with 2 mL doses, a tiny measurement error swings the mg/kg dose a lot. With 7.5 mL, accuracy is much better and safer.

✔️ Better absorption

Levamisole works systemically. If a sheep doesn’t swallow cleanly, blood levels drop and worms survive. This mid-range dose is consistently swallowed and absorbed.

✔️ Much lower aspiration risk

The large-volume mix practically begs to get into the trachea. This one doesn’t.

✔️ Rams tolerate it

This alone is worth its weight in gold.

Storage: Can Levamisole Freeze? Yes.

Levamisole is highly stable in cold temperatures and freezing conditions. If the solution freezes in winter:

• Thaw it

• Shake well

• Use it normally

No loss of potency.

Selective Deworming: I Only Treat Sheep Who Need It

I never blanket-drench the whole flock. Instead, I use FAMACHA scoring:

• Ruby red eyelids → no treatment

• Pale → treated immediately

• Borderline → case-by-case

Selective deworming reduces resistance and keeps levamisole effective for years.

Final Thoughts

Levamisole is powerful and still incredibly valuable but the way the label tells you to administer it doesn’t always translate to the real world. My mid-range formula has been a game-changer here at Wormuth Farm. It’s easier on the sheep, safer, more accurate, and ultimately more effective.

If this helps another shepherd avoid a stressful drenching session (or a ram who won’t look you in the eye for two days), I’m glad to share it.