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

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

Laurie Piper

CSIRO Livestock Industries

Armidale NSW Australia


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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”


Australian livestock production statistics l.jpg

Australian Livestock Production statistics

IndustryProduction 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


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Australian Sheep Production statistics


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Agricultural production zones


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


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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


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Prevalence of resistance (efficacy < 95%)


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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 ?


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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


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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


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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.


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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


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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


Response in csiro h c selection lines l.jpg

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


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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


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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 (%)


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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 weightUnfavourable

    • Body weightUnfavourable

    • ReproductionFavourable


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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


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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


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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


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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


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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


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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


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Technology transfer: the Nemesis program

  • Initiated in 1994

  • A network of breeders, wool growers, advisers, and scientists

  • Established to transfer research results to industry


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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


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Traits recorded by Merino studs (survey results, n=200)

  • Fleece weight80.4%

  • Fibre diameter93.5%

  • CV of fibre diameter91.1%

  • Body weight39.8%

  • Pedigree69.1%

  • Selection index23.6%

  • Estimated breeding values23.6%

  • Faecal egg counts 9.8%


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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


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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


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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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