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 Series • PhD, West Virginia University June 23, 2020 – Impact of sire and breed on Dr. Andrew Weaver parasite resistance in sheep Small Ruminant Extension Specialist North Carolina State University Raleigh, NC 1 2 Parasite challenges are expanding Parasite Challenges • Superfamily Trichostrongyloidea ( Strongylid nematodes) – Haemonchus contortus – Teladorsagia circumcincta ( Ostertagia ) – Trichostrongylus species – Cooperia – Nematodirus • Protozoan parasites – Eimeria (coccidia) 3 4 Parasite Challenges Life Cycle Haemonchus contortus (Barber Pole Worm) • Blood feeder 21 days • Highly prolific • Anemia, decreased performance and death of infected individuals • Millions of dollars in economic losses annually 7-14 days Photo credit: Erin Andrews 5 6 1
6/24/2020 Anthelmintic (Dewormer) Resistance Resistant Susceptible Resistant Male Female “What doesn’t kill you makes you stronger” H. contortus does not bind to epithelial surface of the abomasum! Must swim to maintain position! 7 8 How do we assess parasite burden? Parasite Resistance vs. Resilience • Fecal egg count (FEC) • Resistance: ability of sheep to eliminate parasite infection – Measure of the number of strongylid parasite eggs in 1 gram of fecal matter – Optimal – Can’t distinguish strongylid parasites by egg • Resilience: ability of sheep to continue to perform despite some level of infection • Larval culture required for speciation – Low infection <500 eggs/g – Sheep will “break” at some point – Moderate infection 500-1500 eggs/g – Volcano is ready to erupt but you don’t know when – High infection >1500 eggs/g – FAMACHA scoring great tool for on-farm evaluation • Adult worm burden would be great • Will not tell you actual level of infection • Subjective measurement compared to fecal egg counts but not practical 9 10 Variation in Parasite Resistance Selection Tools • Between breeds • Records – Parasite Resistant – Phenotypic selection – Parasite Susceptible • Estimated Breeding Values (EBV) • Within breed – Quantitative selection – Measure of individual genetic merit – Combines: • Individual performance • Pedigree information Suffolk • Progeny data • “You can’t select for what you don’t measure!” St. Croix Between Breeds Within Breed 11 12 2
6/24/2020 What is true parasite resistance? Immune Genotype Phenotype Response Parasite Resistant St. Croix Suffolk “Hair” “Wool” Parasite Susceptible Adapted from Jacobs et al., 2015 13 14 What happens after larval ingestion? Improved immune cell response! • Greater parasite establishment in parasite-susceptible • Greater cellular response in parasite-resistant (hair) vs. wool sheep compared to parasite-resistant hair sheep parasite-susceptible (wool) sheep Total Worm Burden Delayed response in parasite-susceptible sheep allows time for larvae to establish! Bowdridge et al., 2015 Bowdridge et al., 2015 15 16 Immune cell extracellular traps (NETs) Immune cells bound to the surface of a larvae! Bind up the larvae! Remember, if larvae can’t move, they get flushed out of the gut! Cover photo, Parasite Immunology , Garza, Garza et al., 2018 2018 17 18 3
6/24/2020 Cellular impact on larval survival T-helper type 2 (Th2) polarization • T-helper type 2 Parasite-resistant responses are associated with Parasite-susceptible parasite infection and allergic reactions • “Weep and sweep” response • Increase mucus production and gut contractility • Flush out worms! Measure of larval energy! Lower ATP means greater larval death. MacKinnon et al., 2015 Garza et al., 2018 19 20 Within Breed Selection for Parasite Parasite Resistance Summary Resistance Weep and Sweep Extremely low Extremely high fecal egg count fecal egg count Breed or Flock breeding value breeding value Average Epithelial Damage Larval Expulsion Signaling Cascade 21 22 Genetic Progress Phenotypic Variation • P = G + E • FEC data is not normally distributed • 70/30 rule: 70% of worms are carried by 30% of sheep – Phenotype is a combination of genetics and environment • Example: – 2018 Virginia Tech Suffolk lambs • ∆G = (h 2 + i + σ p ) / L – Range – h 2 : heritability 0-3450 eggs/g – i: selection intensity – σ p : phenotypic variation – L: generation interval 23 24 4
6/24/2020 FEC Estimated Breeding Value (EBV) FEC Estimated Breeding Value (EBV) • Developed at Virginia Tech in the early 2000’s • FEC heritability: 20-25% (moderate) -60% -30% • Reported as a PERCENT CHANGE • Negative values are GOOD Expected FEC difference – Indicates the genetic potential to reduce FEC between lambs sired by EPD = (½)EBV these rams is 25% -10% -5% 25 26 1 1 2 2 3 3 4 5 4 5 Sire PFEC EBV Acc. Sire PFEC EBV Acc. Low FEC EBV High FEC EBV Low Sire 1 -68 94 High Sire 1 348 84 Low Sire 2 -82 94 High Sire 2 104 92 Average → Low Sire 3 -100 85 High Sire 3 510 93 Randomly mated to Low Sire 4 -99 94 High Sire 4 120 82 Katahdin ewe flock High Sire 5 360 82 Low Sire 5 -79 88 at SWVA AREC (Glade Spring, VA) Average -85 Average 288 27 28 Selection Works! FEC EBV: a risk management tool If an enhanced immune response is associated with increased parasite resistance (lower FEC), does FEC EBV predict general immunity and lamb fitness? Sire EBV 29 30 5
6/24/2020 “Trends, like horses, are easier to ride FEC EBV: a risk management tool in the direction they are already going.” Sire EBV NO YES C. perfringens Type A vaccination 31 32 Relationship to other traits Effect of birth/rear type on lamb FEC • Selection for FEC is possible without deleterious effects on growth traits • Weaning and post-weaning FEC highly related Trait 1 Trait 2 Genetic Phenotypic Correlation 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 Birth/Rear Type Adapted from Ngere et al., 2018 Notter et al., 2017 33 34 Effect of dam age on dam post-partum Effect of lamb age on lamb FEC FEC Death Dam age Notter et al., 2017 Notter et al., 2017 35 36 6
6/24/2020 Measuring parasite resistance Timing of fecal collection • Timing of fecal collection – NSIP reports a weaning (60 days) and post-weaning 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 * P < 0.05 challenge infection (second infection) data Sire EBV Natural infection data in Katahdin sheep located in Southwest Virginia 37 38 Sheep need to be challenged! How do we challenge sheep? • After larval exposure, it takes 3 weeks before FEC • Natural infection • Time FEC collection for 4-5 weeks after known parasite – Infection resulting from exposure consumption of larvae on pasture while grazing – Assumes all lambs in a 14-21 days 4-5 weeks First week contemporary group have equal opportunity for infection L4 stage Larvae mature to Collect fecal – Actual level of intake unknown begins adult stage and sample feeding begin shedding – Better representation of ability eggs to handle parasite infection in L3 Larvae addition to environmental (Infective stage) Sheep can die suddenly of acute challenges haemonchosis with no FEC 39 40 How do we challenge sheep? Case Study: Virginia Tech Suffolk flock • Artificial infection • All lambs exposed to grass ~2 weeks post-lambing (Feb) – Used in experimental settings • Ram lambs – Lambs are dosed with 5000-10,000 larvae – Moved to ram test facility early May – Level of intake known for all lambs – Ad libitum feed with access to pasture lots – Improved plane of nutrition and confinement housing – Artificial infection for 4-5 weeks reduce other environmental challenges • Ewe lambs – Developed on grass all summer – Fecal sample prior to any lamb needing dewormed 41 42 7
6/24/2020 Case Study: Virginia Tech Suffolk flock 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 Beyond survival, no selection pressure has been placed specifically on FEC 43 44 Acknowledgements 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 45 46 Questions Contact Information Dr. Andrew Weaver Department of Animal Science North Carolina State University Raleigh, NC 989-708-2557 arweave3@ncsu.edu 47 48 8
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