The value of yeast (Saccharomyces cerevisiae) as a protein supplement for the growth of wool by Merino sheep.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 16 THE VALUE OF YEAST (SACCHAROMYCES CEREVISIAE) AS A PROTEIN SUPPLEMENT FOR THE GROWTH OF WOOL BY MERINO SHEEP R.A.M. AL JASSIM*+, P.J. REIS** and W.R. McMANUS* SUMMARY The value of yeast protein as a supplement for increasing wool growth and nitrogen retention in Merino sheep was investigated in two experiment l In experiment 1, yeast added to a roughage diet at three levels to provide 24, 48 and 72 g crude protein/day failed to increase wool growth. When a further group of sheep were given formaldehyde-treated casein (89 g/day) in the diet wool growth was appreciably increased (2. 80%). In experiment 2, sheep were given abomasal supplements of yeast (89 g crude protein/day), yeast + DL-methionine (2 g/day) and DL-methionine (2 g/day). Yeast protein caused a small reduction in wool growth whereas methionine supplementation appreciably increased wool growth. Nitrogen retention was increased by yeast supplementation in both experiments but changes were not statistically significant in experiment (Keywords: yeast protein, methionine, wool growth, nitrogen retention) INTRODUCTION Yeast protein is generally characterized by its well balanced amino acid profile with respect to essential amino acids but with a slightly low content of sulphur-containing amino acids (c. 2% cysteine plus methionine; Al Jassim and Yeast has been successfully incorporated into the diets of poultry Hogan 1983). and pigs (Shacklady 1975), and as a replacement for milk proteins in the liquid feeding system of lambs (Soliman et al. 1982). The use of single cell proteinaceous products such as yeast in the diet of adult ruminants is limited mainly because of its high cost and the availability of other widely accepted protein sources. The work reported here is part of an intensive study aimed at assessing the value of yeast protein for wool and body growth. Previous digestion studies of Al Jassim et al. (1983) indicated that yeast should be a useful source of supplementary protein for sheep. Particular emphasis was placed on the sulphurcontaining amino acids of yeast in view of evidence regarding their role in the synthesis of wool fibres (Hemsley and Reis 1985). MATERIALS AND METHODS In experiment 1, 42 Merino wethers, aged 12-18 months and weighing an average of 25 kg, were randomised into five groups of 10, 9, 9, 10 and 4 sheep The experimental design involved three periods of 10 weeks each respectively. as indicated in Fig. 1. All sheep were shorn at the beginning of the 1. Kensington, N.S.W., 2033, Australia. ** CSIRO, Division of Animal Production, PO Box 239, Blacktown, N.S.W., 2148. + Present address: Department of Animal Resources, College of Agriculture, University of Baghdad, Baghdad, Iraq. * , School of Wool and Pastoral Sciences, University of New South Wales, PO Box 1, 127 Proc. Aust. Soc. Anim. Prod. Vol. 16 experiment, and woo; growth rate was measured by clipping a tattooed area on the mid-side (c. 100 cm ); results were expressed as clean dry wool per unit area of All sheep were offered 950 g/day dry matter of a loose mixture consisting skin. of equal parts chopped lucerne and wheaten hay once daily. During period 2, yeast supplements were added to diets of groups 2, 3 and 4 to provide each sheep with 24, 48 and 72 g crude protein/day respectively (designated Y1, Y2 and Y3). Group 5 consisted of 4 sheep, each of which received a daily dietary supplement of 89 g formaldehyde-treated casein (FTC). Casein was treated by adding 1.5 g formaldehyde per 100 g casein in a low-volume procedure (Hemsley et al. 1973). During each period two sheep from each group were placed in metabolism cages for digestion measurements. The same sheep were used for the consecutive digestion measurements. Fig. 1. The experimental design used in experiment 1 In experiment 2, eight 2-year old Merino wethers, weighing about 39 kg, were surgically prepared with a permanent cannula in the abomasum close to the The experimental design adopted was the same as experiment 1, with pylorus. Wool growt$ rate was measured by clipping a periods reduced to 4 weeks. Each sheep tattooed area on the mid-side (c. 100 cm ) at intervals of 2 weeks. was offered a daily ration of 770 g dry matter of the roughage diet in a pelleted form, in two equal parts at 0800 and 1200 h, except during the treatment period when seven equal portions were given at intervals of 2 h between 0800 and 2000 h. Two sheep were allocated to each of four treatments: control (R); yeast, 89 g crude protein/day (R+Y); yeast (89 g crude protein) + 2 g/day DL-methionine Supplements of yeast and methionine (R+Y+Met); 2 g/day DL-methionine (R+Met). were injected into the abomasum as a suspension or a solution in 800 ml distilled Digestion and nitrogen water at hourly intervals between 0900 and 1800 h. retention measurements were conducted during both pre-treatment and treatment periods. For both experiments N-retention was calculated as: Fibre diameter was measured by the Fibre Fineness Distribution Analyser (FFDA) (Lynch and Michie 1976). Sulphur content of woolwas estimated by the oxygen flask method as applied to wool by Earland (1961). 128 Proc. Aust. Soc. Anim. Prod. Vol. 16 Table 1 Effect of yeast and formaldehyde-treated casein supplementation on wool growth, fibre diameter and nitrogen retention in experiment 1 * Period: 1 = pre-treatment; 2 = treatment; 3 = post-treatment (covariate) ** Values in this table within a column with different superscripts differ significantly (P < 0.05) Table 2 Effect of yeast and methionine supplementation on wool growth, fibre diameter, sulphur content of wool and nitrogen retention in experiment 2 129 Proc. Aust. Soc. Anim. Prod. Vol. I6 RESULTS Results of experiment 1 demonstrated that incorporation of yeast into the roughage diet did not stimulate wool growth rate, and fibre diameter was not Addition of FTC resulted in a substantial and significantly altered (Table 1). statistically significant (P < 0.05) increase in wool growth rate (about 80%). Nitrogen Fibre diameter also increased significantly (P < 0.05) with FTC. retention appeared to be increased by yeast supplementation (particularly treatment Y3)# but the changes were not statistically significant as measurements were made on only two sheep per treatment (Table 1). However, measurements of live weight showed no differences in growth rate between groups 1-4, whereas sheep in group 5 grew at a. significantly faster rate than the controls (110 VS. 66 g/day). In experiment 2, abomasal administration of yeast caused a slight reduction in wool growth rate whereas supplements of methionine, alone or added to yeast, As there were stimulated wool growth and increased fibre diameter (Table 2). only two sheep per group, initial values for wool growth and fibre diameter Sulphur content of wool (%) was increased by varied appreciably between groups. 8.4% with yeast supplementation and by 24.8% when methionine was added to yeast; Nitrogen methionine alone increased sulphur content by 18.8% (Table 2). retention was increased significantly (P < 0.05) by 178% for the yeast treatments (Y and Y+Met.) and by 22% with methionine (Table 2). DISCUSSION The results of experiment 1 do not support the suggestion of Al Jassim et al. (1983) that yeast protein would be an effective source of supplementary protein for sheep. ' It is apparent that yeast protein is not a useful supplement for wool growth, and its value for the synthesis of tissue proteins is The failure of dietary supplements of yeast protein to stimulate uncertain. wool growth cannot be explained on the basis of amino acid composition or protein The failure of yeast protein to stimulate wool growth when given digestibility. via the abomasum indicates that extensive degradation in the rumen is not the It is possible that some unidentified component in yeast has an explanation. inhibitory effect on wool growth, but no data are available to support this In this connection, the response to methionine may have been suggestion. reduced in the presence of yeast, but more extensive data are needed. REFERENCES AL JASSIM, R.A.M. and HOGAN, J.P. (1983). Proc. Nutr. Soc. Aust. 8: 185. AL JASSIM, R.A.M., HOGAN, J.P. and McMANUS, W.R. (1983). Proc. Nutr. Soc. Aust. 49 EARLANT, C. (1961). Text. Res. J. 31: 2 . HEMSLEY, J.A. and REIS, P.J. (1985). 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