Deworming Sheep and Goats

Deworming Sheep and Goats

By Dr Duncan Houston

If worms are quietly dragging down growth, fertility, milk production, or resilience in your flock, you will often see the effects before you realise parasites are the real driver. That is what makes internal parasites so frustrating in sheep and goats. By the time the problem looks obvious, the performance loss has often been going on for weeks.

Deworming is not just about giving a drench. Effective parasite control means understanding which parasites matter, when treatment is actually needed, and how to avoid making resistance worse. This is especially important in goats and in warm, humid regions where parasite pressure can become relentless.

Quick Answer

Deworming sheep and goats effectively requires more than routine drenching. The best results come from combining pasture management, targeted treatment, fecal monitoring, and resistance testing. Blanket deworming of the whole flock over and over is one of the fastest ways to lose drug effectiveness, especially against barber pole worm.

Why Internal Parasites Matter So Much

Internal parasites reduce productivity long before they kill animals.

They can cause:
• poor growth
• reduced milk production
• poorer feed efficiency
• weight loss
• anemia
• diarrhea
• weakness
• death in severe cases

Goats are often hit harder than many producers expect. In practice, they tend to be more vulnerable because of both grazing behaviour and weaker natural parasite resistance compared with some sheep lines.

Clinical insight:

One of the biggest mistakes I see is waiting for obvious diarrhea or collapse. Many parasite problems are doing damage while animals still look only “a bit behind.”

What Are the Main Worms and Parasites?

Different parasites cause different patterns of disease, but several are especially important in small ruminants.

Barber pole worm (Haemonchus contortus)

This is one of the biggest problems in many flocks.

Why it matters:
• causes blood loss
• leads to anemia
• can cause bottle jaw
• can kill very quickly

This is often the parasite producers underestimate the most because animals may not have much diarrhea, yet they are dangerously compromised.

Other gastrointestinal worms

These can contribute to:
• weight loss
• diarrhea
• poor coat quality
• reduced performance

Examples include:
• Trichostrongylus
• Oesophagostomum
• Nematodirus
• Ostertagia/Teladorsagia
• Strongyloides
• Trichuris

Coccidia and Cryptosporidium

These are especially important in young lambs and kids.

They can cause:
• diarrhea
• dehydration
• poor growth
• rapid decline in young stock

Decision checkpoint:

If young animals are doing badly, do not assume every parasite problem is just “worms.” Coccidia can be a major part of the picture.

What Do Worm Problems Actually Look Like?

Subclinical parasite burden

This is where a lot of production loss happens.

What it looks like:
• slower growth
• rough coat
• poor thrift
• reduced milk yield
• poorer body condition

Clinical parasite disease

This is when the burden is overwhelming the animal.

What it looks like:
• pale gums or eyelids
• bottle jaw
• weakness
• diarrhea
• weight loss
• reduced appetite
• sudden death in severe cases

Clinical insight:

The real concern is not just the worm burden. It is whether the animal is coping with that burden. A modest count in a stressed ewe can matter more than a higher count in a resilient adult.

Severity Framework: How Serious Is It?

Mild

• slightly poor thrift
• mild coat change
• no obvious weakness

What it usually means:
Subclinical loss is already happening.

What to do:
Assess with fecal testing and flock review rather than guessing.

Moderate

• reduced body condition
• mild anemia
• intermittent diarrhea
• poorer growth rates

What it usually means:
Parasites are affecting performance and need active control.

What to do:
Review parasite plan, test, and treat strategically.

Severe

• obvious anemia
• bottle jaw
• significant diarrhea
• weight loss
• weakness

What it usually means:
This is no longer a routine management issue. Disease is established.

What to do:
Treat promptly, reassess drug effectiveness, and involve your veterinarian.

Critical

• collapse
• severe weakness
• very pale mucous membranes
• sudden death risk

What it usually means:
Heavy parasite burden or major parasitic disease complication.

What to do:
Immediate veterinary intervention is needed.

Why Blanket Deworming Fails

This is one of the most important points.

For years, many flocks were managed by routinely drenching everything on a schedule. That approach is now one of the main reasons resistance is such a problem.

Why it fails:
• it treats animals that may not need treatment
• it increases selection pressure for resistant worms
• it gives the illusion of control while effectiveness declines

Clinical insight:

If you keep using the same drugs on the whole flock without checking whether they still work, resistance will quietly build until one day the drench seems to do nothing.

The Three Main Dewormer Classes

Benzimidazoles

Often called the white drenches.

Examples include:
• albendazole
• fenbendazole

Important point:
Resistance is already widespread in many flocks, especially against barber pole worm.

Macrocyclic lactones

Examples include:
• ivermectin
• moxidectin

Important point:
These are useful, but resistance is also common, particularly with ivermectin.

Membrane depolarisers

Examples include:
• levamisole
• pyrantel

Important point:
These may still be effective where other groups are failing, but they also need to be used correctly and carefully.

Decision checkpoint:

Do not assume a drench works just because it worked years ago. Resistance testing matters far more than brand familiarity.

What Is the Best Deworming Strategy?

There is no single perfect protocol for every flock, but good programs usually combine targeted treatment with monitoring.

1. Salvage or targeted deworming

This means treating only the animals that need it.

Common tools:
• FAMACHA scoring
• fecal egg counts
• clinical assessment

Why it helps:
• reduces unnecessary drug use
• slows resistance development
• focuses treatment on the animals driving contamination or showing disease

This is often one of the smartest long-term approaches.

2. Tactical deworming

This means treating around periods of predictable risk.

Examples:
• after weather conditions that drive pasture contamination
• when fecal egg counts rise above meaningful thresholds

This can be useful, but only when based on actual parasite pressure rather than habit.

3. Strategic deworming

This means timing treatment around known biological pressure points.

A major example:
• the periparturient rise around lambing or kidding

This can help reduce pasture contamination from ewes or does under physiological stress.

Clinical insight:

Strategic treatment can be useful, but if every strategic moment turns into repeated whole-flock treatment, resistance pressure builds fast.

Why FAMACHA and Fecal Testing Matter

FAMACHA scoring

This is particularly valuable for barber pole worm because it helps assess anemia.

It does not replace full diagnosis, but it helps identify animals most likely to need treatment.

Fecal egg counts

These help answer:
• whether worm burden is likely significant
• whether treatment is needed
• whether current control is working

Fecal egg count reduction tests

This is one of the best ways to detect resistance.

General principle:
A strong drop after treatment suggests the drench is working. A poor drop suggests resistance.

Clinical insight:

This is one of the most useful tests in flock medicine because it tells you whether your protocol exists in reality or just on paper.

What Should You Do Right Now?

If parasite control is a concern in your flock:

1. Stop relying on calendar-based drenching alone

2. Use fecal testing to understand what parasites are present

3. Check FAMACHA scores regularly in risk periods

4. Review whether your current products are still effective

5. Cull repeat high-shedders or chronically affected animals

Time-based guidance:
• monitor more closely during warm, humid periods
• reassess every few weeks in peak challenge seasons
• use fecal testing every 8 to 12 weeks or as risk dictates

Smart Drenching Matters

Even a good dewormer fails if the technique is poor.

Best practices:
• weigh animals properly
• dose accurately
• use correct administration technique
• avoid underdosing
• use separate equipment where needed
• make sure oral drenches are actually swallowed properly

Underdosing is one of the easiest ways to select for resistant worms.

Pasture Management Is Not Optional

Dewormers alone will not save a badly managed parasite system.

Key pasture strategies:

• rotational grazing
• avoiding overstocking
• reducing exposure of young stock to heavily contaminated pasture
• mixed grazing where appropriate
• giving paddocks rest where feasible

Mixed grazing with cattle can help because cattle do not share the same major worm burdens as sheep and goats.

Decision checkpoint:

If your flock keeps needing treatment over and over, the real issue may be pasture contamination rather than medication choice.

Breeding and Culling for Better Resistance

Some animals cope with worms much better than others.

That matters because:
• parasite resilience has a genetic component
• repeat poor performers increase contamination pressure
• selecting better animals improves long-term flock health

Cull animals that:
• repeatedly need treatment
• stay anemic
• remain poor performers
• carry high burdens again and again

This is one of the strongest long-term flock improvements you can make.

Common Mistakes Producers Make

Deworming the whole flock too often

This speeds resistance.

Using the same product repeatedly without testing

This creates false confidence and worsening failure.

Underdosing

A classic way to breed resistant worms.

Treating signs without identifying the likely parasite

Not all diarrhea is the same, and not all anemia is purely barber pole worm.

Ignoring management

Pasture pressure drives many parasite problems more than people realise.

Keeping chronic poor performers

These animals often cost far more than they are worth.

When Is This an Emergency?

Seek veterinary help urgently if you see:
• severe anemia
• marked weakness
• bottle jaw with collapse risk
• significant diarrhea in young stock
• sudden deaths
• ongoing losses despite treatment

Do not assume the drench “just needs more time” if animals are clearly deteriorating.

FAQ

How often should sheep and goats be dewormed?

There is no safe one-size-fits-all schedule. Treatment should be based on parasite pressure, clinical signs, FAMACHA scoring, and fecal testing.

What is the biggest worm problem in many flocks?

Barber pole worm is one of the most important and dangerous parasites, especially in warm, humid regions.

Why are goats often harder to manage for worms?

Goats are generally more vulnerable to internal parasites and often require especially careful control programs.

How do I know if my dewormer still works?

The best way is fecal egg count reduction testing after treatment.

Should I deworm every animal if one looks bad?

Not automatically. Targeted treatment is often a better strategy unless there is clear evidence of broad flock-level need.

Final Thoughts

Effective deworming in sheep and goats is no longer about finding the strongest drench and using it over and over. That approach is exactly what got many flocks into trouble.

The real goal is:
• fewer treatments
• better timing
• smarter testing
• better pasture management
• slower resistance development

That is what protects productivity long term.

If you want help building a deworming plan, interpreting fecal results, checking for resistance, or deciding which animals actually need treatment, ASK A VET™ can help you make clearer, more strategic decisions for your flock.