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Genetic and phenotypic aspects of foot lesion scores in sheep ofdifferent breeds and ages

Published online by Cambridge University Press:  01 September 2008

G. J. Nieuwhof ,
J. Conington ,
L. Bűnger ,
W. Haresign  and
S. C. Bishop
G. J. Nieuwhof*
Affiliation:
Meat and Livestock Commission, PO Box 44, Milton Keynes MK6 1AX, UK Roslin Institute and Royal (Dick) School of Veterinary Studies, Roslin BioCentre, Midlothian EH25 9PS, UK
J. Conington
Affiliation:
SAC, West Mains Road, Edinburgh EH9 3JG, UK
L. Bűnger
Affiliation:
SAC, West Mains Road, Edinburgh EH9 3JG, UK
W. Haresign
Affiliation:
Institute of Rural Sciences, University of Wales, Aberystwyth SY23 3AL, UK
S. C. Bishop
Affiliation:
Roslin Institute and Royal (Dick) School of Veterinary Studies, Roslin BioCentre, Midlothian EH25 9PS, UK
*
E-mail: [email protected]
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Abstract

Footrot is a costly endemic disease of sheep. This study investigates thepotential to decrease its prevalence through selective breeding for decreasedlesion score. Pedigreed mule and Scottish Blackface (SBF) ewes were scored forlesions on each hoof on a 0 to 4 scale for up to 2 (SBF ewes) or 4 (mules) timesover 2 years. One score was obtained for SBF lambs. An animal was deemed to havelesions (severe lesions) if at least one hoof had a score of at least 1 (2). Theprevalence of lesions was 34% in lambs, 17% in SBF ewes and 51% in mules. Theheritability of lesions (severe lesions) analysed as repeated measurements ofthe same trait in a threshold model was 0.19 (0.26) in SBF ewes and 0.12 (0.19)in mules. Estimates for the sum and maximum of scores as well as the number offeet affected were much lower, as were estimates for permanent animal effects(i.e. non-genetic effects associated with an animal). When successive scores onthe same animal were analysed as correlated traits, heritability estimates formost traits tended to be higher, except for severe footrot in mules whereestimates varied greatly over time. The phenotypic correlations betweensuccessive scores in SBF ewes were close to 0, genetic correlations weremoderately positive (0.18 to 0.55). Correlations in mules were generally of asimilar size, but some genetic correlations were higher (up to 0.92). There wasa clear trend for heritabilities for lesions and severe lesions to increase withhigher prevalence of lesions, even when analysed in a threshold model.Heritability estimates for traits that combine scores over several events inmules, identifying the more persistently affected animals, ranged from 0.12 to0.23 with the highest estimates for the average number of feet that were(severely) affected in animals scored for a minimum at two events. Theheritability of all lesion traits in lambs was estimated as 0. It is concludedthat selection for lower lesions is possible in ewes but not lambs, and that asimple binary score at an animal level is at least as effective as acomprehensive score at hoof level. Given the low repeatability of lesion scores,repeated measures over time will improve effectiveness of selection. Selectionacross environments (flocks, seasons) with different prevalences of lesionsscores will need to take account of variation in the heritability.

Keywords

sheepfootrotprevalencegeneticsrepeatabilityfoot lesions
Type
Full Paper
Information
animal , Volume 2 , Issue 9 , September 2008 , pp. 1289 - 1296
Copyright
Copyright © The Animal Consortium 2008

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