tailieunhanh - Quantitative aspects of ruminant digestion and metabolism - Phần 17

Large variation exists both between and within sheep in the rate of growth, composition and physical characteristics of wool fibres. The rate of clean wool growth can range from less than 1 to greater than 30 g per animal per day | 22 Mathematical Modelling of Wool Growth at the Cellular and Whole Animal Level . Nagorcka1 and M. Freer2 1CSIRO Livestock Industries GPO Box 1600 Canberra ACT 2601 Australia 2CSIRO Plant Industry GPO Box 1600 Canberra ACT 2601 Australia Introduction Large variation exists both between and within sheep in the rate of growth composition and physical characteristics of wool fibres. The rate of clean wool growth can range from less than 1 to greater than 30 g per animal per day. The mean diameter of fibres in the fleece from sheep of ultra-fine wool Merino strains can be as low as 13 mm whereas it is greater than 40 mm for some carpet wool breeds and the diameter of individual fibres can range from less than 10 mm to greater than 100 mm. Diameter can also vary considerably along the length of individual fibres reducing the strength of the wool causing it to become tender and decreasing the commercial value of the fleece. Many fleece staples are highly crimped whereas some have little or no crimp Reis 1992 . The amino acid composition of wool may also vary in particular the sulphur-containing amino acid cystine usually quoted in units of half-cystine so that it is equivalent to the amino acid cysteine may vary considerably Reis 1979 . This variation in wool characteristics is due to both genetic and environmental factors. For each animal the potential rate of wool growth and the morphology and chemical composition of wool fibres growing at their maximum rate are controlled by several genetically determined factors and mechanisms. These were outlined in an earlier publication Black and Nagorcka 1993 . The actual rate of wool growth and the characteristics of the wool fibres are the result of the interaction between the genetic factors and the supply of nutrients to the wool follicles Black 1987 . The latter is influenced by the quantity and type of nutrients absorbed from the digestive tract and the competition for nutrients between wool growth and the growth of .