Cashmere Fibre Diameter and Curvature: Effect of Animal Age and Breedline

Abstract

Effects of selection for increased mean cashmere fleece value (V) or reduced mean cashmere diameter (F) were assessed in Scottish cashmere goats and compared with a randomly bred line (C). Cashmere samples were collected from, and live weights recorded for, animals of two cohorts (n = 10 per breedline / cohort) at 5, 17 and 29 months (Cohort 1) or 5, 17 and 21 months (Cohort 2) of age. For each cashmere sample, mean cashmere fibre diameter (MFD) and associated CV(%), mean cashmere curvature (deg/mm, MCC) and curvature s.d. (CSD) was calculated. In both cohorts animal weight increased with animal age (P>0.01). In animals of Cohort 1, overall MFD increased from 5 to 29 months of age (15.2 to 16.5 µm; P<0.01) and at 29 months, the MFD of V animals was greater than in F animals (17.8 c.f. 15.1 µm; P<0.01). Overall, MCC decreased between 5 and 29 months of age (57.0 to 52.9 deg/mm; P<0.01). At 5 months of age, the MCC of the F line (60.9) was greater than that of the C (55.8) and V (54.3) lines (P<0.05). Using the 5-month values as a covariate, at 29 months, the MCC was greater in F animals than in C (P<0.05) or V animals (P<0.01). In Cohort 2, in all breedlines, MFD increased between 5 and 21 months (15.0 to17.1 µm; P<0.01), becoming greater in V than either C or F animals (17.8, 16.7, 16.8 µm respectively; P<0.01). The overall MCC was less at 17 and at 21 months than at 5 months of age (51.4, 55.4, 58.8 deg/mm respectively; P<0.01). There was no significant effect of breedline on MCC or in the associated CSD. The overall correlation coefficient of MFD with animal age for all animals between 5 and 29 months (Cohort 1, 0.77, P<0.01) and between 5 and 21 months (Cohort 2, 0.78, P<0.01) was significant but varied with breedline. There was a significant relationship between MCC and MFD but this varied with cohort and breedline. Fibre samples taken at 5 months of age were not suitable for prediction of lifetime cashmere diameter or curvature, particularly of V line goats. It is concluded that fibre diameter and cashmere curvature changes, in response to selection, are affected by animal age, breedline and responses of individual animals; therefore these factors should be taken into account in selection of animals for lifetime performance.