2. www.agriculture.vsu.edu
Internal Parasite Control
In the wake of increasing drug resistance,
alternative are needed for effective worm
control
Alternatives include:
Targeted Selective Treatment
Pasture Management
Nutritional Supplementation
Genetic Selection
No alternative by itself will likely be
effective
An integrated approach to worm control is
needed
3. www.agriculture.vsu.edu
Genetic Selection
Genetic selection for resistance or
resilience to internal parasites is a
very important strategy
Identifying and selecting the best
animals for long-term health
builds a more resistant herd/flock
This presentation will focus on
how best to select those animals
with traits of resistance to
internal parasites
5. www.agriculture.vsu.edu
Resistance vs. resilience
Which is better?
Resilient animals are productive
even under parasite challenge
Require less deworming
Resilient animals spread a lot of
internal parasite eggs onto pasture
Causing parasitism in more
susceptible animals (young, old,
non-resistant)
6. www.agriculture.vsu.edu
Resistance vs. resilience
Which is better?
Resistant animals reduce the
need for deworming
Resistant animals reduce the
contamination of pasture
Resistant animals pass their
resistance genes onto the
next generation
7. www.agriculture.vsu.edu
Heritability
Heritability is the portion of trait variation
in a population of animals that are due to
genetic variance
Parasite resistance and resilience are
quantitative traits
Controlled by many different genes
Parasite resistance is a moderately heritable
trait
Heritability estimates for FEC is 20 – 30%
Parasite resilience is less heritable
Selecting lines of animals that have an improved ability to regulate their parasite populations
increases immunity against parasites at the herd level
9. www.agriculture.vsu.edu
Host Immunity
Key factor in determining whether an
animal can resist or allow parasite
infection to establish is host immunity
Controlled by animal genotype
More effective immune response results in
low larval establishment or worm egg
shedding
There are two kinds of immunity:
Innate – present at birth
Acquired/Adaptive – develops as animals
are exposed to parasites
10. www.agriculture.vsu.edu
Host Immunity
Young start to develop immunity
to parasites slowly with exposure
Lambs acquire immunity 4 – 9
months of age
Takes longer in goats (≥ 1 yr. old)
Breed dependent
Regular exposure is necessary to
develop immunity
Immunity may only last for weeks
in the absence of infection
11. www.agriculture.vsu.edu
Host Immunity
Adults (especially sheep) tend to
remain relatively resistant to
infection
Immune response is suppressed
under stress
Low nutrition
Disease
High producing females (multiples,
heavy milkers etc.)
12. www.agriculture.vsu.edu
Host Immunity
Ways to boost immunity
Not placing very young
animals on heavily
infested pastures
Always ensure quality
nutrition to susceptible
animals
Separate and feed females
based on litter size
Use low-stress handling
techniques
13. www.agriculture.vsu.edu
Breed Resistance
There are some breeds that have
been naturally selected for
resistance to internal parasites
Typically, these breeds were
developed in situations and
climates that favored internal
parasites
These animals were selected by
natural selection (“survival of the
fittest”), and are generally more
resistant to worms
14. www.agriculture.vsu.edu
Breed Resistance
Traditionally, identifying animals with
lower levels of infection has been
accomplished by fecal egg counts (FEC)
FEC has allowed us to identify parasite
resistant breeds
Hair sheep – St. Croix, Barbados Blackbelly,
Katahdins
Wool sheep – Texels, Gulf Coast Native, and
Florida Native, Hog Island???
Goats – Spanish, Kiko and Myotonic
15. www.agriculture.vsu.edu
Breed Resistance
Tennessee State University (Dr. Richard
Browning)
Compared reproductive, growth and health
traits among Boer, Spanish and Kiko meat
goats
Annual rates of parasitism were greater
for Boer does (53%) than for Kiko (24%)
and Spanish does (22%)
Postpartum FEC were less for Spanish
and Kiko dams compared to Boer dams
16. www.agriculture.vsu.edu
Crossbreeding
• Mating animals of different breeds is
one way to adding parasite resistance
to your herd/flock
• Breed complementarity - Balance
strengths and weaknesses of different
breeds
• Heterosis (hybrid vigor) - superiority
of crossbred animal as compared to
(weighted) average performance of
purebred parents
17. www.agriculture.vsu.edu
Animal Selection
Selection based on breed
can be an effective tool in
reducing worm loads
Especially in purebred flocks
Within every breed there is a
range in FEC
Individual animals should
always be monitored for
their own merit
18. www.agriculture.vsu.edu
Animal Selection
Important to identify animals that have
lower numbers of worms
More parasite resistant animals
decrease the need for deworming
Culling parasite susceptible animals
will increase flock resistance, reduce
pasture contamination and decrease
deworming frequency
80/20 rule
20% of herd/flock shed 80 percent of the
parasite eggs
Susan Schoenian, Meat Goat Test
19. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
The most accurate way to
identify individual animals
that are parasite resistant is
to measure FEC
Resistant animals will have
low FEC
Do not shed many eggs in
their manure
Immune system
20. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
Accuracy of FEC increases
with multiple samples
Compare samples taken
from similar groups of
animals, during the same
season and year
Information gained from
FEC is very useful and the
best assessment of
resistance in a flock/herd
21. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
Producers can learn to do
their own FEC (workshops
offered)
Offered by many
veterinarians and labs
It can be labor-intensive and
costly
22. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
Measure and record
FEC during the
parasite season
Take at least 2 fecal samples
a month apart
Use when selecting sires
Small differences between
FEC results are not
meaningful
24. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
Kid ID FEC (June, 2017) FEC (July, 2017)
101 500 600
102 450 300
103 No eggs 150 More R
104 800 950
105 2,000 4,750 More S
106 200 700
107 450 1,100
Queen 3,500 6,000 More S
Dixie 900 1,100
111 150 200 More R
112 5,000 2,200 More S
28. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
What data should I be recording?
FAMACHA scores and
deworming frequency
Cull those individuals needing
more than three treatments a
year
Don’t select offspring (especially
males) from animals that require
frequent treatment
30. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
Select the BEST!
The male represents half the genetics
your flock/herd. One male may
influence the genetics of 50 or more
offspring.
If you are saving replacements, the
male will influence 90% of the genetics
in your flock/herd after several years
of use
Why select more resistant females and
breed them to a susceptible or
unknown male?
31. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
Cull the WORSE!
A female only influences
the genetics of her own
offspring, 1-4 per year
Higher producing females,
especially yearlings, are
more likely to have higher
FEC and require
deworming
32. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
National Sheep Improvement Center (NSIP,
http://nsip.org) calculates estimated breeding values
(EBV) for sheep producers and breed associations
EBV’s are science-based, industry-tested
measurements of heritable traits that can be tracked
and measured
EBVs are proven to improve on-farm productivity and
enhance breeding decisions
Currently, Katahdin and Polypay have significant FEC
data for EBVs for parasite resistance
Producers can submit FEC data, regardless of breed
33. www.agriculture.vsu.edu
Selecting Worm Resistant Animals
If you were to breed these rams you would
expect FEC of lambs sired by Ram A to be
25% lower than FEC of lambs sired by B
Adapted from Genetic Selection; Bowdridge
and Weaver
These resilient animals tend to always be wormy (high FEC) yet demonstrate few if any signs of parasitism (good FAMACHA scores etc.)
Hog island resistance due to isolation not necessarily resistance. Wool breeds, especially black faced breeds are more susceptible to parasites. Should be cautious when raising in a [parasite favorable environment