Recessive mutation for low fibre curvature in the wool of sheep

Abstract

Two mating experiments suggest a recessive gene for lustre in the birth coat of the lamb and low fibre curvature of the yearling fleece. Suffolk sheep normally have high wool fibre curvature, but a sire was found that had very low fibre curvature (21.0°/mm). In the first experiment, no lambs were born with a lustrous birth coat among the initial progeny from this sire (n = 32). Fleece samples at weaning (70.0°/mm) and yearling shearing (67.6°/mm) had high fibre curvature with no sign of segregation. All second-generation progeny of this sire (n = 4) were born with a lustrous birth coat, yet none survived to lamb shearing. Breeding was discontinued.In a second experiment, two male lambs were born with lustrous birth coats and low fibre curvature at weaning (29.0°/mm, 20.8°/mm). First generation progeny (n = 17, n = 18) from these sires showed no evidence of lustre of their birth coat, with fleece samples that were relatively high in fibre curvature at weaning (43.1°/mm, 43.8°/mm) and yearling (43.4°/mm, 45.4°/mm) respectively. When one sire was crossed back to the ewe progeny of both (n = 10) there was strong evidence for segregation of lustre of the birth coat. Lustrous lambs (n = 9) had low fibre curvature when shorn at weaning (21.0°/mm) in comparison with lambs (n = 8) with a wild-type birth coat (46.5°/mm) (P < 0.001). Fibre curvature had increased at yearling shearing of those recorded as lustrous at birth (41.6°/mm) but remained significantly lower (P = 0.001) than those that were recorded as wild-type (56.9°/mm). There was also a large difference in medullation between the two phenotypes, where the lustrous birth coat was associated with greater medullation in the fleece at weaning (54.5 %) and again as yearlings (22.5 %), compared with wild-type progeny (9.5 % and 4.0 %) respectively. There was no difference between birth coat types for weaning weight, yearling weight or fibre diameter variation at either age of fleece sampling. Fleece weight was considerably lower (P = 0.001) for yearlings that had lustrous birth coats (1.22 kg) than those with wild-type birth coats (1.76 kg), and though there was no significant difference in fibre diameter at this age, fleece samples taken at weaning were around 3 µm finer in wild-type lambs (P = 0.008). These results suggest a recessive gene for low fibre curvature was segregating in this population.