The digestibility of the nitrogen, amino acids, lipid, carbohydrates, ribonucleic acid and phosphorus of an n‐paraffin‐grown yeast when given to colostomised laying hens

Colostomised hens were given diets containing various levels of n ‐paraffin‐grown yeast in balance experiments to investigate the relationship between protein and amino‐acid intake and digestibility. The yeast was included at levels of 0, 10, 20, 30, 40 and 100% as the sole protein source in semi‐synthetic diets. The digestibilities of the lipid, carbohydrate and RNA, and the digestible and metabolisable energy values of yeast were determined. Level of intake significantly affected the true digestibility of the protein and amino acids of the yeast; the faecal nitrogen and amino‐acid outputs per 100 units of protein tended to be lower at low levels of intake. However, for practical purposes the effect was considered to be small enough to be ignored in the calculation of the digestibility coefficients. The mean true digestibility of the yeast protein was 90.7% and the true digestibilities of the amino acids, with the exception of cystine and tryptophan, were within the range 90 to 96%. Yeast lipid was 73% digestible. The yeast contained 7.2% mannose and 15.8% glucose; these were 71 and 81% digestible, respectively. The mean digestible energy (d.e.) value of the yeast was 3863 kcal/kg. The classical and nitrogen‐corrected metabolisable energy values of the yeast were 3045 ± 88 and 2716 ± 43 kcal/kg, respectively.