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Breeding for parasite resistance in sheep - a clean green strategy now being adopted by Australian sheep breeders

Breeding for parasite resistance in sheep - a clean green strategy now being adopted by Australian sheep breeders. Laurie Piper CSIRO Livestock Industries Armidale NSW Australia. Outline of Seminar. Background on sheep production and the problem of internal parasites

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Breeding for parasite resistance in sheep - a clean green strategy now being adopted by Australian sheep breeders

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  1. Breeding for parasite resistancein sheep - a clean green strategy now being adopted by Australian sheep breeders Laurie Piper CSIRO Livestock Industries Armidale NSW Australia

  2. Outline of Seminar • Background on sheep production and the problem of internal parasites • Breeding for resistance to internal parasites: • Research findings • Technology transfer • The future: • “Sustainable control of internal parasites in sheep”

  3. Australian Livestock Production statistics Industry Production value 2000/01 Sheep $ 4055 m (30%)* Cattle $ 4555 m (34%) Pig meat $ 850 m (6%) Poultry meat $ 1339 m (10%) Milk $ 2681 m (20%) * Percentage of total value of livestock production

  4. Australian Sheep Production statistics

  5. Agricultural production zones

  6. The cost of internal parasites to the wool industry ($million)

  7. Current parasite control strategies • No effective vaccines • Reliance on strategic drenching programs: • Wormbuster (south-east QLD) • Wormkill (northern NSW) • Wormplan (VIC and TAS) • Drenchplan (southern NSW) • Crack and Wormwise (WA) • Rotational grazing with cattle • Limited use of breeding technologies

  8. Prevalence of resistance (efficacy < 95%)

  9. Breeding for resistance to metazoan parasites • Would it be possible ? interacting genomes, genetic variation in resistance of sheep and parasite, relative generation intervals • Would it be better to breed for resilience ? less challenge to the parasite but would it be as effective in terms of host productivity ?

  10. Breeding for resistance in Merinos • Beginning in 1973 - use direct larval challenge and faecal egg counts (eggs/gm) to estimate genetic variation in resistance within flocks (Hc) • By 1977 have reasonable estimates of heritability and genetic correlations with other traits of economic importance • In 1978 begin selection experiments aimed at demonstrating response to selection (Hc and Tc) and creating lines for immunology studies

  11. Breeding for resistance in Merinos • Research findings: • Differences between strains and flocks (studs) • Long term selection lines • Including resistance in breeding programs • Benefits of resistant sheep • Resilience? • Technology transfer: • The Nemesis program

  12. Strain Flock Within Flock Non-Genetic Sources of genetic variation GFW MFD BW Worm resistance Compared to production traits, the differences between strains and studs are small for resistance. The genetic differences for resistance are greatest between animals. Heritability around 0.25.

  13. 1.0 0.8 0.6 0.4 0.2 FEC EBV 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 Sire Differences between sires in CPT • There are large differences between sires in resistance • Sires which are highly resistant may also have high production

  14. Long term selection lines • CSIRO selection lines established in 1978: • H. contortus • T. colubriformis • UNE “Golden Ram” flock • Hamilton selection lines (Victoria) • Rylington Park line (West Australia) • Estimated heritabilities range from 0.2 to 0.3

  15. Susceptible flock 40000 30000 Unselected flock FEC (eggs/gram) 20000 Resistant flock 10000 0 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 Year of Birth Response in CSIRO H.c.selection lines With intense selection, it may be possible to reduce FEC in weaners by up to 50% in around 10 years

  16. Can the parasites respond to the genetic change in the host ? • Parasites passaged through sheep from the susceptible and resistant lines for 30 generations • Relative infectivity of the two populations of passaged parasites compared with control parasites in sheep from the susceptible and resistant lines • No differences observed in infectivity between the three parasite populations

  17. Including resistance in breeding programs • Incorporating resistance in a formal breeding objective is difficult: • Hard to predict the savings due to reduced treatment • Production losses difficult to measure • Desired gains approach: • Economic values for production traits • Specify emphasis to place on resistance (%)

  18. Genetic relationships with production • Correlations in Australian Merinos: • Clean fleece weight 0.08 • Fibre diameter -0.05 • Body weight -0.21 • Reproductive rate -0.14 • New Zealand results (Morris et al, 2000): • Fleece weight Unfavourable • Body weight Unfavourable • Reproduction Favourable

  19. Index WORM50 WORM70 Selection in practice Selection on a production index (INDEX) and on worm resistance (FEC EBV) can be made independently Alternatively, an index including worm resistance can be calculated with moderate (WORM50) or high (WORM70) emphasis on resistance

  20. 2000 1600 Large Bowel Worm 1200 Black Scour Worm FEC (eggs/gram) Small Brown Stomach Worm 800 400 0 Unselected weaners Resistant weaners Susceptible weaners Benefits of selecting for resistance Genetic resistance to worms can be detected by weaning age Resistance extends to different worm species

  21. 6000 5000 Resistant flock 4000 Unselected flock Lambing Faecal egg count (epg) 3000 Susceptible flock 2000 1000 0 Dry -5 -4 -3 -2 -1 0 +1 +2 +3 +4 +5 Weeks Benefits of selecting for resistance Reduced pasture contamination during lambing

  22. 120 100 80 60 % of infective larvaeon pastures 40 20 0 Random Resistant Undrenched Drenched Pasture contamination is reduced greatly by grazing worm resistant sheep rather than drenched animals

  23. Year Rep 1 Rep 2 Rep 3 Rep 4 Rep 5 Rep 6 Rep 7 Rep 8 Rep 9 Rep 10 1 3 3 3 3 3 3 3 3 3 3 2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 3 3 3 3 3 3 3 3 3 3 5 3 3 3 3 3 3 3 3 3 3 6 3 3 3 3 3 3 3 3 3 3 7 3 3 3 3 3 3 3 3 3 3 8 3 3 3 3 3 3 3 3 3 3 9 3 3 3 3 3 3 3 3 3 2 10 2 3 3 3 2 3 3 3 3 2 11 2 2 2 3 1 3 2 3 3 2 12 1 2 1 1 1 3 1 3 2 2 13 1 2 0 1 0 3 1 2 0 1 14 1 1 0 1 0 2 1 1 0 1 15 0 1 0 0 0 2 1 0 0 1 16 0 0 0 0 0 2 0 0 0 0 17 0 0 0 0 0 1 0 0 0 0 18 0 0 0 0 0 1 0 0 0 0 19 0 0 0 0 0 0 0 0 0 0 20 0 0 0 0 0 0 0 0 0 0 Benefits of selecting for resistance: reduced frequency of drenching

  24. Breeding for resilience? • Advantages: • Simplicity • No selection pressure on the parasite • Disadvantages: • Very low heritability • Unable to distinguish between production and disease alleles • Possible compromises to animal health • No epidemiological benefits

  25. Technology transfer: the Nemesis program • Initiated in 1994 • A network of breeders, wool growers, advisers, and scientists • Established to transfer research results to industry

  26. Nemesis structure • 11 core ram breeders who, via Woolmark funding, receive: • FEC measurements on individual animals • EBV’s for FEC, and in some cases, for production traits • Advice on incorporating resistance into their breeding programs • Over 600 breeders, wool growers, advisors, and scientists who receive information via newsletters

  27. Traits recorded by Merino studs (survey results, n=200) • Fleece weight 80.4% • Fibre diameter 93.5% • CV of fibre diameter 91.1% • Body weight 39.8% • Pedigree 69.1% • Selection index 23.6% • Estimated breeding values 23.6% • Faecal egg counts 9.8%

  28. The future: Integrated Parasite Management • “SCIPS” (Sustainable Control of Internal Parasites of Sheep): • More astute and greatly reduced use of anthelmintics • Breeding parasite resistant sheep • Improved grazing management • Better nutrition and enhanced immunity of sheep • Innovative flock management

  29. SCIPS R,D & TT components • Improved diagnostic techniques • Improved knowledge and adoption of sustainable control practices • Computer based models: • Decision support package to assist woolgrowers and advisors • National website • Accelerated adoption of Nemesis • Education

  30. Conclusions • It has been possible to breed sheep for resistance to a metazoan parasite • The model of measuring response to direct challenge with the normal infective form of the parasite exposed substantial additive genetic variation • We are going to use this model in a new attempt to breed sheep for resistance to the sheep blowfly

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