Nutritional evaluation of triple low rapeseed products for growing pigs

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Abstract
Ground full-fat rapeseed (FFRS) and the resulting extracted oil (RSO), meal (RSM) and recombined RSO and RSM (ORSM) from a triple-low cultivar containing low levels of erucic acid, glucosinolates and tannins were evaluated. RSO, FFRS and ORSM were included into a basal diet to give levels of added oil of 40, 80 and 120g/kg. RSM was also incorporated into the basal diet at the same rates as in ORSM. The 12 experimental diets together with the basal diet were given to 13 gilts in a metabolism trial conducted over four time periods. A 10-day acclimatization in holding pens preceded a 5-day total collection of faeces and urine in metabolism crates. Rapeseed products, diets, faeces and urine were analysed for gross energy (GE) and all, except urine, for oil content measured by two methods (petroleum ether and acid hydrolysis prior to ether extraction). Apparent digestible energy (DE) and metabolizable energy (ME) of rapeseed products were determined by single-level assay and by regression. Oil DE was also derived indirectly as a product of apparent oil digestibility (AOD) and oil GE. Apparent nitrogen digestibility was estimated for diets and rapeseed products. The response of dietary DE, ME and AOD to rates of test material inclusion was linear (P < 0·001) in all cases except for ORSM and RSM the DE and ME of which, in addition, showed evidence of curvilinearity. Age of pig had no significant effect on dietary AOD and energy values. Linear regression techniques were better than single level assays (particularly at low rates of inclusion) in determining energy values and gave DE values of 42·4, 190, 14·6 and 25·8 MJ/kg dry matter for RSO, FFRS, RSM and ORSM respectively. Oil DE and AOD were not influenced by method of evaluation. The results of this study indicated improved energy values for FFRS and RSM of a triple-low cultivar over published data for high-glucosinolate varieties but not over data for double-low varieties. In addition it appears that AOD is the main factor determining dietary utilization of FFRS and would need to be considered in order to optimize the nutritive value of FFRS in diets for growing pigs.