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Selecting Worm Resistant Animals
Dahlia O’Brien
Small Ruminant Specialist
Virginia Cooperative
Extension, Virginia State
University
dobrien@vsu.edu
(804) 524-6963
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
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
www.agriculture.vsu.edu
Resistance vs. resilience
Resistance
 Ability of host/animal to limit
infection
 Suppressing establishment of
parasite inside the body
 Suppressing egg laying
 Expelling adults worms (“self-
cure”)
 Assessed by FEC
Resilience
 Ability of host/animal to withstand
challenge/ infection and still
perform
 Assessed by:
 Packed cell volume (PCV)
 FAMACHA© score
 Body condition score (BCS)
 Performance indicators
Resistance and resilience are the two major concepts relating to the animal’s ability to
limit/withstand a worm infection
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)
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
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
www.agriculture.vsu.edu
Host Immunity
 Most Susceptible
 Kids/lambs
 Periparturient females
 Old animals
 Less Susceptible
 Bucks
 Open does
 Pets
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
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
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.)
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
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
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
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
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
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
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
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
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
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
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
www.agriculture.vsu.edu
Selecting Worm Resistant Animals
 All kids and lambs
 Use contemporary
groups (same age,
management etc.)
 Collect fecal samples
when >10% have
FAMACHA © scores ≥3
 Leave out animals that
were previously
dewormed
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
www.agriculture.vsu.edu
Selecting Worm Resistant Animals
 The FAMACHA© system is an
alternative tool for determining
resistant or resilient animals
 Developed in South Africa in response
to the emergence of severe
anthelmintic resistance
 Validated for sheep and goats in the U.S.
 A system to assess anemia due to
Haemonchus contortus (barber pole
worm) infection in sheep and goats
and the need for deworming
individual animals
www.agriculture.vsu.edu
Selecting Worm Resistant Animals
 Simple and inexpensive way to
identify and select animals with
parasite infections (in areas where
barber pole worm is the main
parasite)
 Resilient animals will also have a
good FAMACHA© score even
though they have high FEC
 FEC still recommended to determine
resistance vs. resilience
 FAMACHA© scores and hematocrit
values are highly correlated with
FEC
www.agriculture.vsu.edu
Selecting Worm Resistant Animals
 The Five Point Check©
 Addresses limitations of
FAMACHA by determining
need for deworming for all
internal parasites that affect
sheep and goats
 Useful in deciding whether or
not to deworm FAMACHA
scores of 3’s
 First developed in sheep and
involves 5 check points
 Replace coat (appearance) for nose
in goats
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
www.agriculture.vsu.edu
Selecting Worm Resistant Animals
 Record weights of all
lambs and kids
 To help select which animals
do well under your
production system
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?
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
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
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
www.agriculture.vsu.edu
Selecting Worm Resistant Animals
 Buck kids and ram lambs
 Select and collect fecal samples from
the best 5 – 10
 Deworm to get them clean and at a
similar starting point
 Collect FAMACHA © scores and fecal
samples to measure FEC at 4, 6 and 8
weeks after deworming
 Calculate own “estimated breeding
values” (EBV)
 (Individual FEC – group mean)
X heritability
www.agriculture.vsu.edu
Take away points
 Genetic selection for parasite
resistance is one of the most
promising means to control worms in
a flock/herd
 Keep production traits in mind as well
 Resistant animals, especially the use of
resistant sires leads to lower FEC and
FAMACHA© scores
 Pasture contamination is reduced
when resistant animals are present
 Subsequently reducing the use of
dewormer and death losses

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Selecting Worm Resistant Animals

  • 1. www.agriculture.vsu.edu Selecting Worm Resistant Animals Dahlia O’Brien Small Ruminant Specialist Virginia Cooperative Extension, Virginia State University dobrien@vsu.edu (804) 524-6963
  • 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
  • 4. www.agriculture.vsu.edu Resistance vs. resilience Resistance  Ability of host/animal to limit infection  Suppressing establishment of parasite inside the body  Suppressing egg laying  Expelling adults worms (“self- cure”)  Assessed by FEC Resilience  Ability of host/animal to withstand challenge/ infection and still perform  Assessed by:  Packed cell volume (PCV)  FAMACHA© score  Body condition score (BCS)  Performance indicators Resistance and resilience are the two major concepts relating to the animal’s ability to limit/withstand a worm infection
  • 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
  • 8. www.agriculture.vsu.edu Host Immunity  Most Susceptible  Kids/lambs  Periparturient females  Old animals  Less Susceptible  Bucks  Open does  Pets
  • 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
  • 23. www.agriculture.vsu.edu Selecting Worm Resistant Animals  All kids and lambs  Use contemporary groups (same age, management etc.)  Collect fecal samples when >10% have FAMACHA © scores ≥3  Leave out animals that were previously dewormed
  • 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
  • 25. www.agriculture.vsu.edu Selecting Worm Resistant Animals  The FAMACHA© system is an alternative tool for determining resistant or resilient animals  Developed in South Africa in response to the emergence of severe anthelmintic resistance  Validated for sheep and goats in the U.S.  A system to assess anemia due to Haemonchus contortus (barber pole worm) infection in sheep and goats and the need for deworming individual animals
  • 26. www.agriculture.vsu.edu Selecting Worm Resistant Animals  Simple and inexpensive way to identify and select animals with parasite infections (in areas where barber pole worm is the main parasite)  Resilient animals will also have a good FAMACHA© score even though they have high FEC  FEC still recommended to determine resistance vs. resilience  FAMACHA© scores and hematocrit values are highly correlated with FEC
  • 27. www.agriculture.vsu.edu Selecting Worm Resistant Animals  The Five Point Check©  Addresses limitations of FAMACHA by determining need for deworming for all internal parasites that affect sheep and goats  Useful in deciding whether or not to deworm FAMACHA scores of 3’s  First developed in sheep and involves 5 check points  Replace coat (appearance) for nose in goats
  • 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
  • 29. www.agriculture.vsu.edu Selecting Worm Resistant Animals  Record weights of all lambs and kids  To help select which animals do well under your production system
  • 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
  • 34. www.agriculture.vsu.edu Selecting Worm Resistant Animals  Buck kids and ram lambs  Select and collect fecal samples from the best 5 – 10  Deworm to get them clean and at a similar starting point  Collect FAMACHA © scores and fecal samples to measure FEC at 4, 6 and 8 weeks after deworming  Calculate own “estimated breeding values” (EBV)  (Individual FEC – group mean) X heritability
  • 35. www.agriculture.vsu.edu Take away points  Genetic selection for parasite resistance is one of the most promising means to control worms in a flock/herd  Keep production traits in mind as well  Resistant animals, especially the use of resistant sires leads to lower FEC and FAMACHA© scores  Pasture contamination is reduced when resistant animals are present  Subsequently reducing the use of dewormer and death losses

Notes de l'éditeur

  1. These resilient animals tend to always be wormy (high FEC) yet demonstrate few if any signs of parasitism (good FAMACHA scores etc.)
  2. 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