Effect on wool growth of dietary supplements of normal and treated casein

Abstract

The rate of production of keratinized fibres from skin follicles in sheep can be profoundly influences by nutrition. Some of the earliest controlled experiments demonstrating this fact appear to be those reported by Weber (1931) and Fraser and Nichols (1934). Although there were other reports in the literature which suggested that wool growth was probably affected by nutritional factors, these were concerned with observations of seasonal variations in wool growth of grazing animals (Lush and Jones, 1923; Duerden and Bosman, 1927; Hardy and Tennyson, 1930; Duerden and Bomman, 1927; Hardy and Tennyson, 1930; Burns, 1931).

During the late 1920s and early 1930s a substantial controversy developed around the problem of whether or not the problem of whether or not the sheep could synthesize cysteine (Marston and Robertson, 1928; Barritt and King, 1926, 1929; Rimington, 1929; Rimington and Bakker, 1932; Pollard and Chibnall, 1934). At this time because of the relatively large amount found in wool, cysteine was regarded as an essential amino acid for wool growth. An increase in wool growth due to a supplement of blood meal fed to grazing sheep was inferred by Marston (1932) to be due to the intake of cysteine contained in the blood meal. He also attributed the superiority of a supplement of yeast as compared with casein for wool growth to the higher cysteine content of yeast. The first reported response of wool growth to the administration of a sulphur containing amino acid was given by Marston (1935). The biological significance of methionine was not known at this time. Under normal circumstances, ruminants make inefficient use of high protein diets. It has been shown that some proteins are readily degraded by rumen micro-organisms to ammonia, a large part of which may then be absorbed and excreted as urea. When dietary protein content is high, the extent of protein degradation protein content is high, the extent of protein degradation probably exceeds protein synthesis by rumen micro-organisms (McDonald, 1948). Thus substantial amounts of dietary protein may be lost to the animal. Considerable losses of nitrogen due to ammonia production in the rumen have been demonstrated with protein-rich meals and soluble proteins such as casein (McDonald, 1952; Annison et al., 1954; Chalmers and Synge, 1954). However, nitrogen retention and conversion to animal products such as wool are enhanced when proteins are administered directly into the abomasum or duodenum (Chalmers et al., 1954; Reis and Schinckel, 1963, 1964).

The latest development in the administration of protein into the abomasum or duodenum is to use protein protected from rumen microbial degradation by chemical modification (McDonald, 1967). Any protection procedure would need to leave the protein in a form capable of digestion and absorption further along the alimentary tract so that the protein could be utilized. The pH differential between the rumen, normally above PH6, and the abomasum, normally below pH 3, allows scope for reversal of the effects of coasting or chemical treatments.

Sheep produce wool at the maximal rate of which they are capable for only a brief period in each year (Williams and Schinckel, 1962). Under New Zealand conditions Romney sheep produce three times as much wool and often a break in the staple which results in increased fibre breakage during processing, particularly in combing. Some of this difference can be accounted for by nutrition, and so using pen fed sheep this experiment set out to find whether the trough of wool growth during the minimal period could be partially or completely eliminated by supplementing the basic diet with casein protected from rumen microbial degradation