The consequences of carrying the Booroola fecundity FecB gene on sheep liveweight

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The consequences of carrying the Booroola
fecundity (FecB) gene on sheep liveweight

• G.A. Walling, K.G. Dodds, S.M. Galloway, A.E.
  Beattie, E.A. Lord, J.M. Lumsden, G.W. Montgomery
  J.C. McEwan

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Background Booroola Merino

• Australian high quality wool breed
• Average 2.4 lambs born per ewe
• Mature size 60kg

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Background Romney

• Dual purpose breed
• increasing emphasis on meat
• Mature size
• rams 100-120kg
• ewes 70-90kg
• Inferior to the Booroola Merino for wool and
  fecundity traits

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Management of flocks

• High lambing age flocks require increased
  management
• Pure Booroola genotype is too large for low
  maintenance flocks
• Commercial producers instead use crossbred flocks

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Crossbred Progeny

• Produced to transfer the benefits of high
  fecundity from the Booroola Merino into the
  Romney breed
• Successful at increasing ovulation rate and
  litter size
• Producers report Booroola carriers lighter in
  comparison to equivalent crosses without the
  Booroola gene

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Explanation

• Booroola gene has a pleiotropic effect decreasing
  liveweight
• Locus closely linked to Booroola affecting
  liveweight

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Data

• Animals produced from mating heterozygous sire
  (B) to non-carrier ewes ()
• 401 measurements of weaning weight (WWT) and 581
  measurements of 1½ year old mating weight (MWT)
• Genotyped for 21 DNA markers on sheep chromosome 6

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Methods

• Regression model accounted for sex, contemporary
  group and birth rank
• Estimated the effect on liveweight only at the
  location of the Booroola gene using regression
  (Booroola)
• Interval mapping method testing all locations on
  chromosome 6 (Scan Analysis)

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Results Booroola Analyses
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Results Scan Analyses
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Results Position of liveweight effect
WWT Locus
Booroola Gene
95 Confidence Interval
OOV6
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Results Summary

• The Booroola gene does not have a pleiotropic
  effect on liveweight
• A locus closely linked to the Booroola gene has
  an effect on liveweight
• When adjusted for lighter weaning weights the
  liveweight locus doesnt effect mating weights

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Conclusions

• Booroola gene is closely linked to a locus
  affecting early growth (birth-weaning)
• The low early growth allele hitchhikes with
  the Booroola allele during introgression programs
• The low growth locus is 20cM distal to the
  Booroola gene

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Implications

• Approximately 80 of animals inheriting the
  Booroola allele also inherit the low growth
  allele
• These Booroola carriers (B) are 1.4kg lighter at
  weaning.
• Pure Booroola animals (BB) may be 2.8kg lighter
  at weaning
• Animals lighter at weaning remain lighter at
  first mating

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Further Research

• Assess the effects at older ages in particular
  mature size and slaughter weight
• Break the association between the Booroola allele
  and the low growth allele through recombination

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Acknowledgements

• All staff responsible for the production and
  maintenance of all the flocks used
• Staff responsible for the collection of data
• George Davis, Grant Shackell, Gareth Bruce
• Jude Sise SheepBase editor