Studies on Digestibility, Biological Value and Metabolizable Energy of Single Cell Protein Sources for the Chicken Hiro-omi YOKOTA1, Jun-ichi OKUMURA1, and Yukishige SASA2 1Laboratory of Animal Nutrition, Faculty of Agriculture, Nagoya University, Nagoya-shi 2Animal Health Products Division, Takeda Chemical Industries Ltd., Osaka-shi Yeast grown on sulfite waste liquor has been used as a feed ingredient of chicken for long time. Yeast grown on molasses are commercially also available and used for a feed ingredient of chickens. It has also been developed recently a process to produce yeast grown on acetic acid. This paper deals with the nutritive values of yeasts grown on acetic acid and molasses with or without process of extracting nucleic acid in the chicken. Materials and methods Three kinds of yeast (Candida utilis) were tested. Yeast A was a yeast grown on acetic acid. Yeast B was the same as yeast A except that most of nucleic acid was extracted with sodium chloride. Yeast C was a yeast grown on molasses, of which most of nucleic acid was extracted. Crude protein content of yeasts A, B and C was 58.3, 52.8 and 50.9per cent, respectively. Amino acid composition of these yeasts were estimated with acid hydrolyzates by Hitachi KLA-3 amino acid analyzer and shown in table 1. Twelve colostomized adult single comb White Leghorn cockerels weighing 1.8 to 2.1kg were kept individually in metabolism cages and divided into 3 groups of 4 birds each and given 80g of pelleted experimental diets once a day. After prefeeding of the experimental diets for 4 days, urine and feces were separately collected for the following 3 days. The experimental birds were subsequently fed a protein-free diet in the same regimen to determine endogenous urinary and fecal Table 1. Amino acid composition of yeast used in the present study (g/16g of N). nitrogen excretion. The birds were weighed at the beginning and end of each experimental and collection periods. During the experimental period, the birds were allowed Received January 28, 1976
YOKOTA et al.: Nutritive values of single cell protein 125 to drink water ad libitum. The composition (g/kg) of a protein-free diet was: corn starch 814, soybean oil 80, alminium silicate 10, cellulose powder 15, agar-agar 10, vitamin mixture 12.2, mineral mixture 56.3, choline chloride 2.5. The compositions of vitamin and mineral mixture were described elsewhere1). In the yeast A, B and C diets, corn starch was replaced by 171.5g of yeast A, 189.5g of yeast B or 196.4g of yeast C, respectively, to make dietary crude protein level 10per cent. The diets were pelleted after mixing. Determined crude protein contents of yeast A, B, C and protein-free diets were 10.47, 10.69, 10.53 and 0.49per cent, respectively. Nitrogen determination was made by semimicro Kjeldahl procedure. Energy contents were estimated using Bomb calorimeter. Results and discussion Body weight change, nitrogen intake and excretion in feces and urine of the experimental birds fed the experimental diets were shown in table 2. From these data, apparent and true digestibilities, biological value and net protein utilization value were calculated and shown in table 3. Body weight change and nitrogen intake of birds fed yeast A, B and C diets were relatively similar, however, nitrogen excretion in feces of birds fed yeast A diet was significantly (p<0.05) lower than those of birds fed yeast B and C diets. Nitrogen excretion in urine of birds fed yeast A diet was relatively higher than those of birds fed yeast B and C diets, though not significant statistically. Those data were reflected on both Table 2. Body weight change and N intake and output of birds fed 3 kinds of yeast diets1. are statistically significant (p<0.05). Table 3. Digestibility and biological value of yeast protein (%)1.
126 Japan. Poultry Sci., 13 (4), 1976 Table 4. Metabolizable energy of yeast diets (per day per bird)1. apparent and true digestibilities and biological values which were shown in table 4. Apparent and true digestibilities of the protein of yeast A were 86 and 90per cent, respectively, and those values were about 8 and 9per cent significantly better than those of yeasts B and C, respectively (p<0.05). It might be said that extraction of nucleic acid from yeast should decrease the digestibility of yeast protein. MORIMOTO and YOSHIDA2) reported that the digestibility coefficient of sulfite waste liquor grown yeast crude protein was 77.9per cent. VAN WEERDEN et al.3) reported a mean digestibility coefficient of yeast protein grown on gas oil was 80per cent. Apparent digestibilities of crude protein of both yeasts B and C were well comparable with those of yeasts grown on sulfite waste liquor and gas oil and yeast A showed a higher coefficient. Biological value of yeast A had a trend to be less than those of yeasts B and C. The difference could be due to the differences of amino acid composition of the three yeasts. Protein concentrates as a feed ingredient should be considered not only in digestibilities but also in biological value. Thus it is useful to present the ratio of retained nitrogen to intake nitrogen (net protein utilization value). Net protein utilization value was also presented in table 3. The values of three kinds of yeast used in the present experiment were relatively the same. Compared with the true digestibility and biological value of various protein concentrates reported by OKUMURA and TASAKI4), all of the protein of yeasts tested in the present experiment can be classified as good protein sources. Net protein utilization values of the yeasts used in the present experiment was also very good and next to fish meal that was 70per cent. The results of metabolizable energy determination were shown in table 4. Energy excretion in feces of birds fed yeast A diet was significantly (p<0.05) lower than those of birds fed yeast B or C diets. Energy excretion in urine of birds fed three kinds of yeast diets were quite the same. From these data, metabolizable energy value (M. E.) of the yeast was calculated using the following equation. where a is M.E. (kcal/g) of the yeast diet, b is M.E. (kcal/g) of the protein-free diet,
YOKOTA et al.: Nutritive values of single cell protein 127 3.52 is M.E. (kcal/g) of corn starch5), c is proportion of yeast in the diet, and X is M. E. (kcal/g) of yeast. Metabolizable energy value of the three kinds of yeast was not statistically different from each other, however, yeast grown on acetic acid was the highest being 3.84 (kcal/g) and yeast grown on molasses and extracted nucleic acid was the lowest being 3.08 (kcal/g). KOSAKA et al.6) reported that the metabolizable energy value of n-paraffin grown yeast was between 3.38 and 2.51 (kcal/g) and that of sulfite waste liquor grown yeast was 2.16 (kcal/g). VAN WEERDEN et al.3) showed that the mean metabolizable energy value of yeast grown on gas oil was 2.55 (kcal/g). KOSAKA et al.6) also reported that, when nucleic acid was to some extent extracted from yeast grown on sulfite waste liquor, there was a trend of increasing energy value. In the present experiment, however, nucleic acid extraction from yeast grown on acetic acid had a trend of decreasing energy value. Summary Nutritive values of yeast grown on acetic acid and of to some extent nucleic acid extracted yeasts grown on acetic acid or molasses were studied using colostomized chickens. 1. Apparent and true digestibilities of crude protein of yeast grown on acetic acid were the highest among them, being 86 and 90per cent respectively and those were about 9per cent higher than rest of them. 2. Biological values and net protein utilization values of three kinds of yeasts varied from 77 to 82 and 66 to 69per cent respectively and there was no statistical significance among them. 3. Metabolizable energy values (kcal/g) of yeast grown on acetic acid and yeasts grown on acetic acid or molasses but to some extent nucleic acid extracted were 3.84, 3.55 and 3.08, respectively. 4. It was showed that the extraction of nucleic acid from the yeast had a trend of decreasing protein digestibility and metabolizable energy value of the yeast itself. Acknowledgement The authors are indebted to Takeda Chemical Industries Ltd., for providing yeasts. Literature 1. NESHEIM, M.C., J.D. GARLICH and D. T. HOPKINS: J. Nutr., 78, 89, 1962. 2. MORIMOTO, H. and M. YOSHIDA: Bull. Natl. Inst. Agr. Sci., G13, 107, 1957. 3. VAN WEERDEN, E.J., C.A. SHACKLADY and P. VAN DER WAL: Br. Poultry Sci., 11, 189, 1970. 4. OKUMURA, J. and I. TASAKI: Japan. Poultry Sci., 10, 37, 1973. 5. YOSHIDA, M. and H. HOSHII: Japan. Poultry Sci., 5, 37, 1968. 6. KOSAKA, K., H. HOSHII and YOSHIDA, M.: Japan. Poultry Sci., 9, 159, 1972.
128 Japan. Poultry Sci., 13 (4), 1976