title: Genetic and phenotypic aspects of foot lesion scores in sheep of                     different breeds and ages.
abstract: Footrot is a costly endemic disease of sheep. This study investigates the                    potential to decrease its prevalence through selective breeding for decreased                    lesion score. Pedigreed mule and Scottish Blackface (SBF) ewes were scored for                    lesions on each hoof on a 0 to 4 scale for up to 2 (SBF ewes) or 4 (mules) times                    over 2 years. One score was obtained for SBF lambs. An animal was deemed to have                    lesions (severe lesions) if at least one hoof had a score of at least 1 (2). The                    prevalence of lesions was 34% in lambs, 17% in SBF ewes and 51% in mules. The                    heritability of lesions (severe lesions) analysed as repeated measurements of                    the 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 of                    feet affected were much lower, as were estimates for permanent animal effects                    (i.e. non-genetic effects associated with an animal). When successive scores on                    the same animal were analysed as correlated traits, heritability estimates for                    most traits tended to be higher, except for severe footrot in mules where                    estimates varied greatly over time. The phenotypic correlations between                    successive scores in SBF ewes were close to 0, genetic correlations were                    moderately positive (0.18 to 0.55). Correlations in mules were generally of a                    similar size, but some genetic correlations were higher (up to 0.92). There was                    a clear trend for heritabilities for lesions and severe lesions to increase with                    higher prevalence of lesions, even when analysed in a threshold model.                    Heritability estimates for traits that combine scores over several events in                    mules, identifying the more persistently affected animals, ranged from 0.12 to                    0.23 with the highest estimates for the average number of feet that were                    (severely) affected in animals scored for a minimum at two events. The                    heritability of all lesion traits in lambs was estimated as 0. It is concluded                    that selection for lower lesions is possible in ewes but not lambs, and that a                    simple binary score at an animal level is at least as effective as a                    comprehensive score at hoof level. Given the low repeatability of lesion scores,                    repeated measures over time will improve effectiveness of selection. Selection                    across environments (flocks, seasons) with different prevalences of lesions                    scores will need to take account of variation in the heritability.
authors.affiliation: 1Meat and Livestock Commission,                     PO Box 44, Milton Keynes MK6 1AX,                     UK.
authors.forename: G J
authors.initials: GJ
authors.lastname: Nieuwhof
authors.forename: J
authors.initials: J
authors.lastname: Conington
authors.forename: L
authors.initials: L
authors.lastname: Bűnger
authors.forename: W
authors.initials: W
authors.lastname: Haresign
authors.forename: S C
authors.initials: SC
authors.lastname: Bishop