Biological evaluation of rapeseed meal, soya-bean meal and casein fed to the weanling and the mature rat

Abstract

1. The biological evaluation of solvent and prepress-solvent processed rapeseed meals RM(S) and RM(PS) was carried out with the weanling (phase 1) and the mature (phase 2) rat. The nutritional indices measured were compared with those for diets containing soyabean meal SM and casein CS.2. The true nitrogen digestibility (td(N)) for RM(S), RM(PS), SM and CS in the weanling rat was (%) 78.9 f±1.2, 77.9±2.7, 90.4±0.9 and 96.0±0.6 (P < 0.01) respectively. Net protein utilization was (%) 68.9±10.1, 65.6±3.5, 80.6±4.8 and 81.7±3.1 (P < 0.05) respectively. Biological value was (%) 83.0±7.9, 84.1±5.6, 8.90±5.1 and 85.0±3.4 (P < 0.05) respectively. The same indices when measured in the mature rat showed an increase over those obtained in the weanling rat.3. The growth-promoting effects of the test diets were evaluated over a period of 8 weeks withad lib. feeding between phases 1 and 2. Protein efficiency ratio averaged 2.0±0.14, 1.9±0.35, 2.4±0.39 and 2.3±0.25 for the RM(S), RM(PS), SM and CS treatments respectively.4. The daily endogenous urinary N excretion was 1.58±0.14 mg N/basal kcal or 254 mg N/kg body-weight for the weanling rat and 0.16 mg N/basal kcal or 18 mg N/kg body-weight for the mature rat. Metabolic faecal N excretion was 98.0±9.3 mg N/kg body-weight, or 27.9% of the total N output for the weanling rat, and 37.9±7.2 mg N/kg body-weight, or 67.3% of the total N output for the mature rat during the ‘protein-free’ feeding periods.5. The fresh weight of the thyroid gland per kg metabolic body size was 70, 90, 40 and 40 mg respectively for the RM(S), RM(PS), SM and CS dietary treatments.6. The moisture content of the carcasses was 66.9±3.1, 63.6±2.3 and 64.2±2.2 and the protein content on a dry-matter basis was 55.9±9.6, 50.2±6.4 and 53.1±4.9 for the RM (S and PS), SM and CS diets respectively. The results suggest an increased lean body mass in the rats receiving the rapeseed meal treatments.7. Under the conditions of this experiment solvent-extracted rapeseed meal was superior to prepress-solvent meal on the basis of rat growth response and of results for nutritional indices. Both rapeseed meals were inferior to soya-bean meal and casein.