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Selecting Worm Resistant Animals

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Presentation from 2020 Weekly Worm Webinar Series. Presentation by Dr. Dahlia O'Brien from Virginia State University.

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Selecting Worm Resistant Animals

  1. 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. 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. 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. 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. 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. 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. 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. 8. www.agriculture.vsu.edu Host Immunity  Most Susceptible  Kids/lambs  Periparturient females  Old animals  Less Susceptible  Bucks  Open does  Pets
  9. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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

Editor's Notes

  • 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
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