Hair curvature underpins structural diversity and function in mammalian coats, but what causes curl in keratin hair fibres? To obtain structural data to determine one aspect of this question, we used confocal microscopy to provide measurements of the two cell types that make up the cortex of merino wool fibres, which waschosen as a well-characterised model system representative of narrow diameter hairs, such as underhairs. We measured orthocortical and paracortical cross-sectional areas, and cortical cell lengths, within individual fibre snippets of defined uniplanar curvature. This allowed a direct test of two long-standing theories of the mechanism of curvature in hairs. We found evidence contradicting the theory that curvature results from there being more cells on the side of the fibre closest to the outside, or convex edge, of curvature. In all cases, the orthocortical cells close to the outside of curvature were longer than paracortical cells close to the inside of the curvature, which supports the theory that curvature is underpinned by differences in cell type length. However, the latter theory also implies that, for all fibres, curvature should correlate with the proportions of orthocortical and paracortical cells, and we found no evidence for this. In merino wool, it appears that the absolute length of cells of each type and proportion of cells varies from fibre to fibre, and only the difference between the length of the two cell types is important. Implications for curvature in higher diameter hairs, such as guard hairs and those on the human scalp, are discussed.

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A flock of New Zealand Wiltshire sheep was divided into two lines and selected for increased greasy fleece weight or decreased greasy fleece weight as yearlings. Wiltshires shed their fleece annually, and although these yearlings may have expressed shedding as lambs in the preceding summer, they were shorn in autumn at 5 months and again in spring at 12 months of age to determine fleece weight before the subsequent shedding. A rapid separation in fleece weight was observed within 8 years, with ewe (0.89 kg) and ram yearlings (0.92 kg) selected for increased fleece weight producing significantly more wool (P < 0.001) than ewe (0.43 kg) or ram yearlings (0.39 kg) from the line selected for decreased fleece weight. There was no significant difference between sexes, and the sex × line interaction was not significant. Clearly this was very low wool production, but fleece weight was heritable (h2 = 0.57 ± 0.04). Shedding was scored from 0 (not shed) to 5 (completely shed) for all animals (n = 2505 records) and was found to be heritable in December (h2 = 0.39 ± 0.04) and again in January (h2 = 0.52 ± 0.05), but less so in September at shearing (h2 = 0.24 ± 0.03). Fleece weight in spring was negatively correlated with shedding score in January, both phenotypically (–0.52 ± 0.02) and genetically (–0.81 ± 0.04). Selecting yearlings for low fleece weight developed a shedding sheep with negligible fleece, which may not require shearing. Selecting for shedding of lambs in January would likely achieve a similar outcome.

The area of naturally bare skin around the perineum was scored at weaning in lambs (n = 2152) from a composite flock of New Zealand crossbred sheep. Breech bareness was scored on a range from 1, where wool was growing right to the edges of the anus, to 5, where a large bare area surrounded the perineum. Bareness on the under surface of the tail was measured on a linear scale at tail docking. Dag score (degree of breech soiling) was recorded at weaning, on a scale of 0–5, where an increasing score indicated more dags. Dag score was taken as a measure of the risk of flystrike in the breech. Female lambs tended to have slightly greater (P < 0.001) breech bareness score (mean score 2.7) than males (mean score 2.6), whereas mean dag score of females was lower than that of males (0.45 v. 0.53; P < 0.05). Breech bareness score had a heritability of 0.33 ± 0.06, and the length of bare skin under the tail had a heritability of 0.59 ± 0.06. The genetic correlation between breech bareness score at weaning and length of bare skin under the tail at docking was positive (0.35 ± 0.10). These 2 traits had phenotypic correlations with dag score of –0.17 ± 0.02 and –0.03 ± 0.03, respectively, and genetic correlations with dag score of –0.30 ± 0.13 and 0.03 ± 0.12, respectively; negative values indicated a favourable relationship. Tails were removed at docking, so the phenotypic correlation of about zero between tail data and dag score at weaning was of little utility. Our results suggest that selecting for these 2 bareness traits could reduce dag formation and the associated risk of breech strike.