RESUMO
A study was conducted to 1) investigate the influence of rapeseed cultivar on the range of variation in the chemical composition and feed value of rapeseed meals (RSM) for broilers and 2) to compare between single-cultivar RSM and a batch of UK-sourced proprietary rapeseed meal. Chemical composition was determined for a total of 10 single-cultivar RSM produced via prepressed solvent-extraction and a proprietary RSM. To investigate RSM digestibility a total of 360 birds were housed, six birds per pen, and between day 13 to 21 of age they received a diet containing per kg 250 g RSM and 750 g basal feed based on wheat and soybean meal. Titaniumdioxide (7 g/kg) was added as an inert marker. For the determination nitrogen-corrected metabolisable energy (AMEn) total excreta and feed intake were quantified over the last 4 d of the experiment. On the final day of the experiment ileal digesta were collected for determination of preceacal crude protein digestibility (pcCPD). With the exception of neutral detergent fibre (NDF), glucosinolates and soluble non-starch polysaccharides the coefficients of variation (CV%) for all major components were similar across all RSM (0.5 < CV% < 0.6). Glucosinolate contents were highest in the 10 single-cultivar RSM whereas NDF levels were greater in the proprietary RSM. Across the 10 single-cultivar RSM there was no significant effect of cultivar on AMEn or pcCPD. Pre-planned orthogonal contrasts indicated that the mean AMEn content and pcCPD of the proprietary RSM was significantly lower than the 10 single-cultivar RSM (p < 0.001). In view of the above, processing rather than cultivar appears to be the main driver of nutritional value in RSM fed to broilers.
RESUMO
The chemical characteristics of rapeseed meal (RSM) produced from two cultivars of UK-grown rapeseed, by both supercritical carbon dioxide extraction (ScCO2) and cold-pressed hexane extraction (CpHe) were examined. Their nutritional value, with and without protease, was then assessed in a broiler digestibility trial. Basal feed was substituted with one of four RSM batches (200 g/kg) following adjustments for dry matter (DM) and ether extract (EE) content. Half of each diet was supplemented with a mono-component protease derived from Bacillus subtilis (Axtra®PRO, Danisco Animal Nutrition, Malborough, UK) giving a total of eight test diets. Two control diets, with and without protease were also fed. At 13 d age male Ross 308 broilers were randomly allocated to seven replicate pens (five birds per pen) and assigned to one of 10 diets. Total excreta were collected from 17 to 21 d age and feed intake was recorded. Pre-caecal protein digestibility (pcPd) was determined using TiO2 as an indigestible marker. Colourimetrically CpHe RSM was substantially darker than ScCO2 counterparts. The influence of oil recovery method (ORM) was also evident in DM, EE, ash free neutral detergent fibre (aNDFom), neutral detergent insoluble crude protein (NDICP) and glucosinolate content (GLS). The content of DM, EE and GLS was higher in ScCO2 RSM whereas aNDFom and NDICP levels were greater in CpHe RSM. Protein solubility in KOH was greater in ScCO2 RSM whilst levels of NDICP were lower. Collectively these results suggest that less heat damage was incurred to the RSM during ScCO2 extraction. There was no significant main effect of cultivar nor were any significant interactions observed between treatment factors. Rapeseed meal ScCO2 produced greater metabolisable energy, pcPd, nitrogen retention and energy metabolisability (p < 0.05). Protease supplementation increased pcPd (p < 0.05) irrespective of ORM and cultivar. The key implications of these findings are that by adopting oil recovery methods that minimise the exposure of RSM to thermal treatments and by adding a compatible protease there is scope to increase the nutritional value of RSM for broilers and increase its utilisation in modern poultry production.
