Lysine and other amino acids

Wool protein contains a low level of Lys (Table 17.1), mainly present in the low sulphur-proteins. The bulb cells of the wool follicle are more closely related to 'normal' body cells and require Lys to support a high rate of cell division (Hynd, 1989). Provision of zein protein, which is lacking in both Lys and Tyr, markedly depresses bulb cell mitotic activity, fibre diameter and wool growth rate but not fibre length in Merino sheep (Reis, 1989). Supplementation of Lys to zein protein can reverse such a detrimental effect (Reis and Tunks, 1978). Omission of Lys from a mixture of 13 amino acids (including all indispensable amino acids) infused into the abomasum of Merino sheep depressed fibre diameter and volume but not fibre length, and resulted in weak fibres (Reis and Tunks, 1978). However, there is a lack of knowledge of the effect of Lys on wool production by sheep fed on 'normal' diets. In Angora wether goats, an intraperitoneal infusion of Lys from 1.2 g day"1 up to 5.9 g day"1 with 1 g day"1 Met for 28 days caused a linear decrease in the percentage of fibres that were medullated and greasy mohair production; fibre length and total N balance were unchanged (Smuts-Ayers and Sahlu, 1996). In contrast, provision of 2 g day-1 Lys by peritoneal infusion to Angora goats increased fibre length and reduced fibre diameter with no effect on N balance (Sahlu and Fernandez, 1992). These results indicate that Lys may influence fibre growth under severe Lys deficient conditions and is most likely to exert an effect through changes in cell division in the follicle bulb.

In other studies, an injection of a mixture of Lys, Arg, Val and Thr (7.1, 3.1, 5.2 and 4.1 g day \ respectively) into the abomasum of Merino ewes in late pregnancy did not increase wool growth rate (Stewart et al., 1993). Infusion of a mixture of Lys, Leu, lie and Gly (7, 7, 6 and 1.5 g day-1) into the abomasum of mature Merinos also did not change wool growth rate or fibre diameter (Reis et al., 1990). The omission of Arg, His, Phe, Thr and Val from a mixture of 13 amino acids infused into the abomasum of Merino sheep also had no appreciable effects on wool growth, whereas the omission of Leu or lie from the mixture caused reductions in wool growth studied with two sheep (Reis and Tunks, 1978). Based on these data, some of which are generated from a small number of animals, with the exception of Met, the supply of indispensable amino acids is unlikely to limit wool production in sheep fed normal diets.

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