[1] Univ Cambridge, Dept Vet Med, Cambridge, England
[2] Wellcome Trust Sanger Inst, Hinxton, Cambs, England
[3] Univ Cambridge, Dept Genet, Cambridge CB2 3EH, England
[4] Univ London, Royal Vet Coll, N Mymms, Herts, England
[5] Univ Cambridge, Dept Clin Med, Cambridge, England
[6] Univ Hull, Sch Biol Biomed & Environm Sci, Kingston Upon Hull HU6 7RX, N Humberside, England
[7] Anim Hlth Trust, Ctr Prevent Med, Newmarket, Suffolk, England