Nutritive value of Nigerian rubber seed ( Hevea brasiliensis) meal and oil. IV. Effects of graded levels of rubber seed meal and oil on energy and nitrogen utilization by growing rats

Abstract

Two experiments were conducted to determine the effects of graded levels of rubber seed meal (RBSM) and rubber seed oil (RBSO) on energy, dry matter and nitrogen (N) digestibility, and N retention of growing rats. In the first experiment, RBSM replaced 25, 50, 75 and 100% of the protein contributed by the soya-bean meal (SBM) in the control diet. The 100% RBSM substitution was either unsupplemented or supplemented with amounts of dl-methionine and l-lysine calculated to make up their concentrations to the minimum recommended National Research Council levels. In the second experiment, maize oil (MO) and RBSO replaced maize starch at 3, 6 and 9% in a 2 × 3 factorial arrangement of treatments. The diets in both experiments were iso-nitrogenous, containing 17% (Experiment 1) and 15% (Experiment 2) crude protein on a fresh weight basis. In Experiment 1, significant reductions were obtained in dry matter, energy and N digestibility, in absolute N retention and in the percentage of digested N retained ( P < 0.01) as the level of RBSM increased. Supplementation of the 100% RBSM protein diet with methionine and lysine did not reduce the depressions in the digestibility of energy, dry matter and N, but it significantly improved N retention. In Experiment 2, the inclusion of RBSO at the three levels did not affect the digestibility of dry matter, N or energy, or N retention.