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Influence of birth coat type on fibre characteristics in Merino sheep

J J Olivier*, A P Pretorius & A F Botha1

Grootfontein ADI, Middelburg, 5900, South Africa

1CSIR (TEXTEK), PO Box 1124, Port Elizabeth, 6000, South Africa


Variation in birth coat type in Merino lambs is well documented. In practice, lambs with a hairy birth coat is culled in an attempt to reduce fibre diameter, change in fibre diameter with increased age, and the so called "coarse edge" (generally defined as 5% and more fibres stronger than 30 μ). Recent advances in measurement of fibre diameter and its variation within a staple, allow the quantification of the "coarse edge" which is mainly responsible for the scratchiness in some wool garments. All animals born during the spring of 1992 in the Grootfontein Merino studs were categorised in four groups according to there birth coat type namely: woolly (n=226), more woolly than hairy (n=316), more hairy than woolly (n=157) and hairy (n=33). Midrib wool samples were taken from all animals at six and twelve months of age. The samples were analysed by means of a FDA which measures 8 000 snippet fibres in each sample. Mean fibre diameter, coefficient of variation (cv) and "coarse edge" (percentage fibres stronger than 30 μ) were recorded for each individual sample. Change in fibre diameter from 6 to 12 months of age was calculated for individual animals. Least square methods were used to analyse the data and the mixed model included birth coat type, sex and weaning status as fixed effects and sires as a random effect. Fibre diameter at 12 months ranged from 16.53 to 25.09 μ and coarse edge from 0.7% to 14.8%. Fibre diameter at 6 and 12 months of age and change in fibre diameter, from 6 to 12 months of age, were not influenced significantly by birth coat type. However, cv and coarse edge increased significantly (P<0.01) at both 6 and 12 months as the birth coat type became more hairy. At 12 months of age, heritabilities for fibre diameter, cv and coarse edge were 0.39 ± 0.17, 0.33 ± 0.13 and 0.19 ± 0.09 respectively. The phenotypic correlation between fibre diameter and cv was -0.16 and 0.65 between fibre diameter and coarse edge. A 10% change in fibre diameter will therefore result in a -2.37% change in cv and 40.86% change in coarse edge. Selection against hairy birth coats will probably reduce cv and coarse edge but not fibre diameter or change in fibre diameter from 6 to 12 months of age. The most effective means of reducing coarse edge will thus be to select for a lower fibre diameter which, in addition to reducing coarse edge, will also have a direct economical effect.



Proceedings 33rd SASAS congress