The effect of breed type and inbreeding on characteristics of the fleece and skin of 12-week-old lambs

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Abstract
Sheep of three pure breeds, the Scottish Blackface, South Country Cheviot and Welsh Mountain, and the crosses among these breeds, were inbred mostly by younger-parent offspring matings for three generations. Observations on lambs at 12 weeks of age were weight of fleece per unit area of skin, mean and variance of fibre length, both primary and secondary follicle density, and fibre diameter. The observations were analysed for the effects of inbreeding of the lamb and its dam, breed type, parity, and the sex and birth type of the lamb. Variation in the traits was also analysed for their relationship to lamb's live weight.Secondary follicle density and the density ratio (Ns/Np) decreased with inbreeding of the lamb. Primary follicle density increased whilst secondary fibre diameter and mean fibre length decreased with inbreeding of the dam. The effects of inbreeding on the density ratio and on secondary fibre diameter were correlated with inbreeding effects on the lamb's 12-week live weight. For other traits inbreeding did not have a clear-cut effect. Heterosis observed in F2 lambs was in general greater than that previously recorded for F1. For mean fibre length and mean fibre diameter the comparison of the crossbred deviations from mid-parent of the F2 and inbred lambs suggested epistatic interactions were involved. The effect of inbreeding crossbreds and inbreeding purebreds was different for secondary follicle density and primary fibre diameter, the two traits most clearly exhibiting heterosis in the F2. Lambs from first parity ewes had finer primary fibres and lighter fleece samples than had lambs from later parities.