Understanding Parasite Susceptibility and Native of central - - PDF document

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6/24/2020 My Background Understanding Parasite Susceptibility and Native of central Michigan BS, Michigan State University Resistance MS, Virginia Tech Terminal sire options for hair sheep production Suffolk U Webinar

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Understanding Parasite Susceptibility and Resistance

Suffolk U Webinar Series June 23, 2020

  • Dr. Andrew Weaver

Small Ruminant Extension Specialist North Carolina State University Raleigh, NC

My Background

  • Native of central Michigan
  • BS, Michigan State University
  • MS, Virginia Tech

– Terminal sire options for hair sheep production

  • PhD, West Virginia University

– Impact of sire and breed on parasite resistance in sheep

Parasite challenges are expanding Parasite Challenges

  • Superfamily Trichostrongyloidea (Strongylid nematodes)

– Haemonchus contortus – Teladorsagia circumcincta (Ostertagia) – Trichostrongylus species – Cooperia – Nematodirus

  • Protozoan parasites

– Eimeria (coccidia)

Parasite Challenges

Photo credit: Erin Andrews

Haemonchus contortus

(Barber Pole Worm)

  • Blood feeder
  • Highly prolific
  • Anemia, decreased performance

and death of infected individuals

  • Millions of dollars in economic

losses annually

Life Cycle

21 days 7-14 days

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  • H. contortus does not bind to epithelial surface of the

abomasum! Must swim to maintain position!

Anthelmintic (Dewormer) Resistance Male Female Resistant Susceptible Resistant “What doesn’t kill you makes you stronger” How do we assess parasite burden?

  • Fecal egg count (FEC)

– Measure of the number of strongylid parasite eggs in 1 gram of fecal matter – Can’t distinguish strongylid parasites by egg

  • Larval culture required for speciation

– Low infection <500 eggs/g – Moderate infection 500-1500 eggs/g – High infection >1500 eggs/g

  • Adult worm burden would be great

but not practical

Parasite Resistance vs. Resilience

  • Resistance: ability of sheep to eliminate parasite

infection – Optimal

  • Resilience: ability of sheep to continue to perform

despite some level of infection – Sheep will “break” at some point – Volcano is ready to erupt but you don’t know when – FAMACHA scoring great tool for on-farm evaluation

  • Will not tell you actual level of infection
  • Subjective measurement compared to fecal egg counts

Variation in Parasite Resistance

  • Between breeds

– Parasite Resistant – Parasite Susceptible

  • Within breed

Suffolk

  • St. Croix

Within Breed Between Breeds

Selection Tools

  • Records

– Phenotypic selection

  • Estimated Breeding Values (EBV)

– Quantitative selection – Measure of individual genetic merit – Combines:

  • Individual performance
  • Pedigree information
  • Progeny data
  • “You can’t select for what you don’t measure!”

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6/24/2020 3 Genotype Phenotype

Immune Response

Parasite Resistant Parasite Susceptible

What is true parasite resistance?

  • St. Croix

“Hair” Suffolk “Wool”

Adapted from Jacobs et al., 2015

What happens after larval ingestion?

  • Greater parasite establishment in parasite-susceptible

wool sheep compared to parasite-resistant hair sheep

Bowdridge et al., 2015

Total Worm Burden

Improved immune cell response!

  • Greater cellular response in parasite-resistant (hair) vs.

parasite-susceptible (wool) sheep

Bowdridge et al., 2015

Delayed response in parasite-susceptible sheep allows time for larvae to establish!

Immune cell extracellular traps (NETs)

Garza et al., 2018

Bind up the larvae! Remember, if larvae can’t move, they get flushed out of the gut! Immune cells bound to the surface of a larvae!

Cover photo, Parasite Immunology, Garza, 2018

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Cellular impact on larval survival

Garza et al., 2018

Parasite-resistant Parasite-susceptible

Measure of larval energy! Lower ATP means greater larval death.

T-helper type 2 (Th2) polarization

  • T-helper type 2

responses are associated with parasite infection and allergic reactions

  • “Weep and sweep”

response

  • Increase mucus

production and gut contractility

  • Flush out worms!

MacKinnon et al., 2015

Parasite Resistance Summary

Signaling Cascade Epithelial Damage Larval Expulsion Weep and Sweep

Breed or Flock Average Extremely low fecal egg count breeding value Extremely high fecal egg count breeding value

Within Breed Selection for Parasite Resistance

Genetic Progress

  • P = G + E

– Phenotype is a combination of genetics and environment

  • ∆G = (h2 + i + σp) / L

– h2: heritability – i: selection intensity – σp: phenotypic variation – L: generation interval

Phenotypic Variation

  • FEC data is not normally distributed
  • 70/30 rule: 70% of worms are carried by 30% of sheep
  • Example:

– 2018 Virginia Tech Suffolk lambs – Range 0-3450 eggs/g

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FEC Estimated Breeding Value (EBV)

  • Developed at Virginia Tech in the early 2000’s
  • FEC heritability: 20-25% (moderate)
  • Reported as a PERCENT CHANGE
  • Negative values are GOOD

– Indicates the genetic potential to reduce FEC

FEC Estimated Breeding Value (EBV)

  • 60%
  • 10%
  • 30%
  • 5%

Expected FEC difference between lambs sired by these rams is 25% EPD = (½)EBV

Average →

Low FEC EBV High FEC EBV Randomly mated to Katahdin ewe flock at SWVA AREC (Glade Spring, VA)

1 3 2 5 4 1 3 2 5 4

Sire PFEC EBV Acc. Low Sire 1

  • 68

94 Low Sire 2

  • 82

94 Low Sire 3

  • 100

85 Low Sire 4

  • 99

94 Low Sire 5

  • 79

88 Average

  • 85

Sire PFEC EBV Acc. High Sire 1 348 84 High Sire 2 104 92 High Sire 3 510 93 High Sire 4 120 82 High Sire 5 360 82 Average 288

Selection Works!

Sire EBV

If an enhanced immune response is associated with increased parasite resistance (lower FEC), does FEC EBV predict general immunity and lamb fitness?

FEC EBV: a risk management tool

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FEC EBV: a risk management tool

  • C. perfringens Type A

vaccination

YES NO

Sire EBV

“Trends, like horses, are easier to ride in the direction they are already going.” Relationship to other traits

  • Selection for FEC is possible without deleterious effects
  • n growth traits
  • Weaning and post-weaning FEC highly related

Adapted from Ngere et al., 2018

Trait 1 Trait 2 Genetic Correlation Phenotypic Correlation WFEC WWT

  • 0.29
  • 0.07

PFEC PWWT 0.01

  • 0.02

WFEC PFEC 0.82 0.29

WFEC: Weaning fecal egg count, WWT: Weaning weight, PFEC: Post-weaning fecal egg count, PWWT: Post-weaning weight

Effect of birth/rear type on lamb FEC

Birth/Rear Type

Notter et al., 2017

Effect of dam age on dam post-partum FEC

Dam age

Notter et al., 2017

Effect of lamb age on lamb FEC

Death

Notter et al., 2017

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Measuring parasite resistance

  • Timing of fecal collection

– NSIP reports a weaning (60 days) and post-weaning FEC (120+ days) – Average FEC for contemporary group should exceed 500 eggs/g – Wait until lambs begin showing signs of parasitism (FAMACHA ≥ 3), collect fecal on ALL lambs, deworm

  • Selective deworming breaks contemporary group

structure

  • Primary infection (first infection) data less accurate then

challenge infection (second infection) data

Timing of fecal collection

Weaning

* * *

*P < 0.05 Sire EBV Natural infection data in Katahdin sheep located in Southwest Virginia

Sheep need to be challenged!

  • After larval exposure, it takes 3 weeks before FEC
  • Time FEC collection for 4-5 weeks after known parasite

exposure

First week L4 stage begins feeding Larvae mature to adult stage and begin shedding eggs Collect fecal sample L3 Larvae (Infective stage) Sheep can die suddenly of acute haemonchosis with no FEC 14-21 days 4-5 weeks

How do we challenge sheep?

  • Natural infection

– Infection resulting from consumption of larvae on pasture while grazing – Assumes all lambs in a contemporary group have equal opportunity for infection – Actual level of intake unknown – Better representation of ability to handle parasite infection in addition to environmental challenges

How do we challenge sheep?

  • Artificial infection

– Used in experimental settings – Lambs are dosed with 5000-10,000 larvae – Level of intake known for all lambs – Improved plane of nutrition and confinement housing reduce other environmental challenges

Case Study: Virginia Tech Suffolk flock

  • All lambs exposed to grass ~2 weeks post-lambing (Feb)
  • Ram lambs

– Moved to ram test facility early May – Ad libitum feed with access to pasture lots – Artificial infection for 4-5 weeks

  • Ewe lambs

– Developed on grass all summer – Fecal sample prior to any lamb needing dewormed

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Case Study: Virginia Tech Suffolk flock

Beyond survival, no selection pressure has been placed specifically on FEC

Summary

  • Selection opportunities exist and work!

– Significant phenotypic variability even within a breed traditionally labelled as “parasite susceptible”

  • Sheep need to be challenge
  • Progress may not be immediate, give it some time and

trust the numbers!

  • Selection for parasite resistance may result in a

“tougher” sheep, resistant to more than just worms

Contact Holly Burdett or Dr. Katherine Petersson, University of Rhode Island for more information on sample submission urisheepandgoat@etal.uri.edu Contact Rusty Burgett for more information of NSIP membership info@nsip.org

Acknowledgements Questions Contact Information

  • Dr. Andrew Weaver

Department of Animal Science North Carolina State University Raleigh, NC 989-708-2557 arweave3@ncsu.edu

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