Abstract:
Proc. Aust. Soc. Anim. Prod. Vol. 17 RELATIONSHIP BETWEEN THE RATE OF CHANGE IN FIBRE DIAMETER AND STAPLE STRENGTH K.A. HANSFORD* and J.P. KENNEDY* 415 Although Orwin et al. (1985) suggested that changes in fibre composition contribute to changes in fibre strength, it is believed that diminution of fibre diameter (FD) is the main cause of reduced strength (Bigham et al. 1983). Because it is not clear whether it is minimum FD or the rate of change in FD that determines staple strength (SS), we compared these. Four groups of 6 or 7 merino ewes housed for 12 months were treated as follows: Control, constant plane of nutrition; Drought, gradual decline in nutrition then grain feeding followed by a gradual recovery; High/Low, similar to Drought but without grain feeding; and Pregnant/Lactating, fed estimated requirements to maintain maternal liveweight. The strength of staples from the midside of the fleece was measured and profiles of diameter along the staple were produced by the technique of Hansford et al. (1985). The rate of change in FD between the minimum and maximum FD (w/mm) was calculated and this is referred to as the slope (Fig. 1.) SS of the wools ranged from 14 to 64 N/ktex. Group means (N/ktex) were: Control, 59 of: 5.3 (SD); Drought, 20 t 4.7; High/Low, 32 + 11.4; Pregnant/Lactating, 29 + 11.9. Across all ewes the correlation between the slope and SS was r = -0.74 (P < 0.01) showing that the more rapid the change in FD (steeper slope), the lower was SS. After removing the treatment effect, the correlation was r = -0.43 (P < 0.05) (Fig. 2.). The corresponding correlations between minimum FD and SS were 0.64 (P < 0.01) and 0.27 (NS), respectively. Therefore more of the variation in SS can be explained by slope than can be explained by FD alone. The SS of the Drought and High/Low groups differed significantly (P < 0.05) however the minimum FD did not, illustrating that minimum FD does not account for all the variation Figure 1 Staple diameter profile Figure 2 Correlation - SS vs slope REFERENCES BIGHAM, M.L., SUMNER, R.M.W., HAWKER, H. and FITZGERALD, J.M. (1983). Proc. N.Z. Soc. Anim. Prod. 43: 74. HANSFORD, K.A., EMERY, G.B. and TEASDALE, D.C. (1985). Wool Tech. Sheep Breed. 33: 1, 25. . ORWIN,D.G.F., WOODS, J.L. and GOURDIE, R.G. (1985). Proc. 7th Int. Wool Text. Res. Conf., Tokyo & 193. *Department of Wool Science, University of N.S.W., Kensington, N.S.W., 2033: