Anthelmintic resistance (AR)
• When deworming fails
to achieve expected
1. When deworming fails
to alleviate clinical
2. When deworming fails to
reduce fecal egg count
by 95 percent or more.
• Is widespread and
• Varies by species,
and individual farm.
• Is affected by past
deworming and grazing
. . . is inevitable!
No treatment is 100% effective.
Practices which accelerate drug resistance
1) FREQUENT DEWORMING
3) Injecting dewormers
4) Pouring on dewormers
5) Feeding dewormers
6) “Persistent activity” dewormers
7) Putting dewormer in mouth
8) Dosing on full stomach
9) Deworming when infection levels
(in animal and on pasture) are low.
10) Putting treated animals on clean
11) Treating everyone.
12) Improper use and storage of
How do you know which
anthelmintics work on your farm?
Anthelmintic didn’t work (?) Anthelmintic worked (?)
You should test for anthelmintic
resistance every 2-3 years
Fecal egg count reduction test Drenchrite® larval assay
Fecal egg count reduction test (FECRT)
• Collect fecal samples (> 200 epg) at time of
anthelmintic treatment and 7 to 14 days later.
• Calculate % reduction in fecal egg counts (epg).
2,650 epg on 6/27 (F1)
Dewormed with levamisole
200 epg on 7/11 (F2)
[(F1-F2)/F1] x 100
[(2650-200)/2650] x 100
= 92.5% FECR
• Prepare and send pooled fecal sample (> 350-500 epg) from
at least 10 animals to parasitology lab (e.g. Dr. Ray Kaplan’s
lab @ University of Georgia) where eggs are
isolated, incubated, and allow to hatch and develop into 3rd
• Tests all three classes of anthelmintics simultaneously
• Also identifies worm species.
95-100% effective. Small number of
resistant worms may be present.
80-95% effective. Treatment
is effective, but resistance is
Less than 80%. Production
losses become apparent as
effectiveness of dewormer
moves closer to zero.
Adapted from Wormer
Resistance “The need for
change” Meat Promotion Wales
How effective are your dewormers?
Targeted selective treatment (TST)
Identifies those animals which
Identifies which animals would
benefit from treatment.
#2 - Back - Body condition score (BCS)
• Many worms can cause a loss of body condition.
• Poor or declining body condition can also be a
sign of age, poor nutrition, or other diseases.
• Animals also vary in their ability to carry and hold
Body condition scoring (BCS)
• Is used to determine how fat
or thin an animal is.
• Cannot be determined by
simply looking at an animal.
• Is accomplished by feeling for
the amount of fat and muscle
over the back, ribs, and loin.
• Is one of the most useful
Should be done on a regular
Body Condition Scoring Goats
Score Spineous process Rib cage Loin eye
1 Very thin
Easy to see and feel,
Easy to feel and can feel
No fat covering
Easy to feel, but
Smooth, slightly rounded,
need to use slight pressure
Smooth, even fat
Smooth and rounded Smooth, even feel
Smooth, even fat
Can feel with firm
pressure, no points can
Individual ribs cannot be
felt, but can still feel indent
Smooth, no individual
vertebra can be felt
Individual ribs cannot be
felt. No separation of ribs
Thick fat covering,
may be lumpy and
Langston University resources on
body condition scoring
(similar to FAMACHA card)
#3 - Tail - dag score
• The hindquarters of the animal are assessed to
determine dag score or degree of fecal soiling.
• Many worms can cause scours (diarrhea).
• Stress and diet are other causes of diarrhea.
What are dags?
• Dried feces left dangling on the wool on a
sheep’s rear end.
Score Description Action
No fecal soiling at all. No indication for
Very slight soiling on edge of tail/on
2 Slight soiling on edge of tail/on each side Usually none
3 Moderate soiling, dag formation
4 Severe soiling, severe dag formation
Very severe, watering diarrhea
extending to hocks.
Source: University of Pretoria
#4 - Bottle jaw
(submandibular subcutaneous edema)
• An accumulation of fluid
(swelling) under the
lower jaw of a
sheep, goat, or calf.
• Usually a result of anemia
• Occurs primarily due to
the infestation of barber
pole worms (Haemonchus
contortus) or other blood-
#5 - Coat condition
• The condition of a goat’s hair coat can be indicative of its
overall health and thriftiness.
• At the Western Maryland Research & Education Center, we
use a scoring system of 1-3, where 2 is average coat quality.