This document discusses strategies for targeted selective treatment (TST) to control internal parasites while reducing anthelmintic resistance. It describes several on-farm decision tools for TST, including the FAMACHA eye anemia system, Five Point Check, and performance indicators like weight gain, body condition, and fecal egg counts. Proper use of these tools involves treating only animals showing signs of infection like anemia, bottle jaw, diarrhea or poor weight gain/condition, while leaving a portion of healthy animals untreated to preserve drug susceptibility. Combining multiple indicators is recommended over relying on any single method.
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Deworming tools for small ruminants
1. To Deworm or not
On-farm decision-making tools for
deciding who to treat and when
SUSAN SCHOENIAN SHEEP & GOAT SPECIALIST SSCHOEN@UMD.EDU
2. Anthelmintic resistance
Worms have developed varying degrees of resistant to all dewormers and dewormer classes.
0
20
40
60
80
100
Benzimidazoles Ivermectin Levamisole Moxidectin
Maryland Virginia Georgia
5-10 years ago. 2016-17 ASI Let’s Grow
3. Treatment strategies for worm control
Suppressive
▪ Whole-group
treatment at
regular
intervals.
Strategic
▪ Whole-group
treatment at
strategic
times, such as
before
parturition or
at weaning.
Targeted
▪ Whole-group
treatment,
based on
marker of
infection.
Targeted selective
▪ Individual
treatment
based on
marker of
infection.
REFUGIA BASED CALENDAR BASED
4. What is REFUGIA?
▪ Latin term for “in refuge”
▪ Portion of worm population which has not been
exposed to drug(s); therefore, is still susceptible to
treatment with drug(s).
▪ When resistant worms mate with susceptible worms, a
portion of the offspring can be still killed by the drug.
▪ The challenge is balancing the need for refugia with the
need to treat animals to maintain an acceptable level
of productivity.
Only R S + R
Tx No Tx
5. The concept of leaving a proportion of animals
untreated, with the aim to maintain parasite
populations in refugia is now widely accepted as
the best means of preserving anthelmintic
susceptibility within the parasite population.
6. Targeted Selective Treatment (TST)
▪ Treating only a portion of the flock or
herd.
▪ Only treating animals that require or
would benefit from treatment.
▪ Requires having tools that can easily
be implemented on the farm, chute-
side.
▪ Balance between delaying drug
resistance and maintaining
productivity.
20. 1. Nose
Snotty noses: a clear or
purulent nasal discharge
may be indicative of nasal
bots.
Nasal bots are caused by
the bot fly, Oestrus ovis.
Infection is usually milder
in goats.
Ivermectin is highly effective against all stages of the larvae.
22. 3. Jaw
“Bottle jaw” Submandibular edema hypoproteinaemia
Accumulation of liquid under the jaw. Soft, cool, pitting edema. Swelling under
jaw.
23. 4. Back – body condition score
1 – emaciated
2 – thin
3 – average
4 – fat
5 – obese
Body condition scoring has
many uses on a sheep and goat
farm.
It is an assessment of the
amount of muscle and fat
covering the backbone and the
short ribs of each animal.
Half scores are used.
24.
25. 5. Tail: fecal soiling
▪ Parasites which cause a decrease in
body condition score, may also cause
mild to severe diarrhea.
▪ Animals suffering from the worst
diarrhea are most likely to benefit from
deworming.
▪ As with other check points, there are
many causes of diarrhea, but parasites is
a major one.
▪ It is proposed that only animals showing
overt signs of diarrhea be treated
26. What else should you consider when making
deworming decisions?
▪ Frequency of scoring
▪ Hair coat condition
▪ Pot belly
▪ DISCO (diarrhea score)
Based on dry matter of feces
▪ Performance indicators
▪ Fecal egg count (FEC)
27. Performance-Based Indicators
▪ Non-Haemonchus parasites cause
loss of body weight and condition
and diarrhea (scours).
21% of farms in ASI Let’s Grow
Study to determine anthelmintic
resistance had < 60%
Haemonchus contortus.
30
40
50
60
70
80
90
100
% HAEMONCHUS CONTORTUS
28. The Happy Factor™
▪ The Happy Factor™ decision-support model discriminates
between animals that are likely to respond favorably to
treatment vs. those that are not.
▪ Lambs which fail to reach target weights are dewormed;
those that do not, are not.
▪ Target weights are determined by modeling and are a
measure of nutrient efficiency: energy deposited ÷ energy
consumed.
▪ Requires bi-weekly weighing; works best with precision-
farming technology.
▪ Happy Factor™ model results in less dewormer use, while
maintaining productivity.
29. Will the Happy Factor™ concept work on Delmarva?
▪ The Happy Factor™ has only been
evaluated in temperate climates
where non-Haemonchus worms
predominate (UK, NZ).
▪ In 2017, Vista View Farm
(Damascus, MD) conducted a
SARE-funded study to look at the
feasibility of using real-time
generated rate-of-gain to
determine deworming need where
Haemonchus is primary parasite
(97% according to larvae ID).
31. What about using fecal egg counts as a decision
making tool for deworming?
▪ Not a highly accurate test, especially
at low numbers.
▪ Short pre-patent period of most
parasite makes FECs not very useful
in high challenge environments.
▪ No widely accept threshold for
treatment.
▪ Not farmer-friendly, not chute-side
33. Performance indicators for worm control
WEIGHT GAIN
▪ Lambs/kids that
fail to meet
performance
targets are
dewormed.
MILK YIELD
▪ Higher-producing
dairy females are
dewormed.
▪ For the same
reason, does and
ewes raising
multiples could
be targeted for
deworming.
▪ Also, yearlings.
BODY CONDITION
▪ A portion of the
flock/herd is left
untreated.
▪ The females in
the poorest body
condition are
dewormed.
FECAL EGG COUNT
▪ Deworm animals
when fecal egg
count reach a
certain threshold.
▪ Do fecal egg
counts on
animals with
other indicators.
34. The decision to deworm should be based on a
mixture of factors. There is no one size fits all.