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Confirmation of the presence of a major gene for fecundity in Thoka Cheviot sheep by segregation analyses G.A. Walling 1 , S.C. Bishop 1 , R. Pong-Wong 1 , G. Gittus 2 , A.J.F. Russel & S.M. Rhind 2 1 Roslin Institute (Edinburgh), Roslin, Midlothian, EH25 9PS, UK

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Confirmation of the presence of a major gene

for fecundity in Thoka Cheviot sheep

by segregation analyses

G.A. Walling1, S.C. Bishop1, R. Pong-Wong1, G. Gittus2, A.J.F. Russel & S.M. Rhind2

1Roslin Institute (Edinburgh), Roslin, Midlothian, EH25 9PS, UK

2Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, UK

MESSAGE

This study shows the presence of afecundity gene in Thoka Cheviot sheep

The allele substitution effect increases litter size by 0.6 lambs per litter

  • Aims

  • Use segregation analysis to:

  • Demonstrate segregation of the putative Thoka gene

  • Estimate the size of the effect

  • Estimate the frequency of the allele

  • 5. Results

  • Including a permanent environmental effect in the model did not influence

  • the results

Posterior distribution of the major gene effect for litter size

  • 2. Introduction

  • Putative Thoka gene originates in Icelandic sheep

  • Reported to increase fecundity

  • Named after the ewe in which the fecundity effect was first detected

  • Introduced into the UK in 1985 from imported Icelandic semen

  • Crossbred into Cheviot sheep

  • Prolific ewes retained in the flock

  • Possible carrier rams used for mating

  • 6. Conclusions

  • This study shows the presence of a fecundity gene in Thoka Cheviot sheep

  • The allele substitution effect increases litter size by 0.6 lambs per litter

  • The analysis is able to produce probabilities of each individual animal

  • being each of the three possible Thoka genotypes (TT, T+ and ++)

  • This can be used for detecting carrier ewes for future breeding

  • 3. Data

  • 982 litter size records from

  • 333 ewes

  • Pedigree of 806 animals

  • Collected over 13 years

  • Up to 5 parities per ewe

Litter size distribution in the Thoka Cheviot flock

  • 7. Future Work

  • Combine phenotypic data with marker data to identify the

  • location of the gene

  • Produce and investigate the effect in Thoka homozygote animals

  • 4. Methods

  • Segregation analysis:

  • MCMC Gibbs Sampler with a burn-in of 10,000 iterations

  • 10,000 realisations drawn (1 every 50 iterations)

  • Combined with (flat) priors to produce posterior probability distributions

  • Assuming:

  • A purely additive model due to absence of homozygous Thoka (TT) animals

  • Polygenic heritability fixed at 0.1 (estimated from several other studies)

USE

The Thoka gene can be used

to maintain productivity whilst reducing stocking rates

Acknowledgements

The Thoka experimental programme is funded by the

Scottish Executive Environment and Rural Affairs Department (SEERAD)