C Rymer, D I Givens and P Kirton
Nutritional Sciences Research Unit, School of Agriculture, Policy and Development, The University of Reading, Reading RG6 6AR
Factors affecting the protein quality of rapeseed meal were investigated. The effect of rapeseed variety was studied by selecting five different varieties (Canberra, Fortress, Gemini, Royal and Winner) taken from three different locations (Cambridgeshire, Hampshire and Northumberland). Samples were divided in two and one subsample of each variety x location combination was extracted with ether on a laboratory scale to produce a simulated rapeseed meal. The whole seeds and meals were analysed for chemical composition, amino acid availability (in chickens) and degradability and digestibility (in ruminants) using in vitro techniques. No substantial differences between varieties were observed. The effect of processing mill was investigated by taking samples of rapeseed meal from Unitrition in June and October, Cargill in October, and ADM in December, and these samples were analysed for chemical composition, amino acid availability in chickens (in vivo) and rumen protein degradability (in situ). There was no evidence that selecting rapeseed meal from a particular processor would achieve a consistent improvement in the protein quality of rapeseed meal.
A range of different treatments was applied to rapeseed meal with the aim of improving its protein quality for ruminant and monogastric animals. The efficacy of the different treatments was estimated in vitro. For ruminant animals, treatments consisted of heating the meal to different temperatures for different times in the presence and absence of water and with the application or otherwise of pressure. The two treatments that resulted in the greatest increase in predicted digestible undegradable protein content involved dry heating rapeseed meal in an oven at 800C for 80 min (RUM1) or at 1300C for 20 min (RUM2). When evaluated in situ, RUM2 reduced (P<0.001) the effective degradability of rapeseed meal (outflow rate 0.06 h-1) and increased (P<0.01) the undegradable protein content of rapeseed meal by 9%. For monogastric animals, treatments consisted of adding a cell wall degrading enzyme and a phytase, alone or in combination, to rapeseed meal. The greatest predicted increase in protein digestibility was achieved when the cell wall degrading enzyme was added at rates of 0.4 (POU1) and 0.6 (POU2) g enzyme/kg rapeseed meal dry matter. However, when evaluated in vivo, the availability of methionine, cystine, threonine, tryptophan, leucine, phenylalanine and histidine was lower with POU1 than with untreated rapeseed meal.
It is technically and economically feasible to produce rapeseed meal with higher protein quality for ruminant animals (one product is already on the market). It would be possible to do the same for monogastrics, although different approaches would be needed. The advantage of the monogastric market is year-round demand for product, and there is great potential for increasing inclusion rate of rapeseed products in diets. Constraints to be overcome would be the high fibre and relatively low protein content of rapeseed meal (achievable if a means of decorticating the seed could be developed) and increasing the availability of amino acids (achievable by omitting the use of moist heat in the removal of solvent). Further constraints involve reducing the concentration of sinapine (for laying hens) and increasing the palatability of rapeseed meal (which might be achieved by further reducing the concentration of glucosinolates).