Nutritive value of coarse and fine wheat brans for rabbits

Abstract

The objective of this study was to compare the nutritive value of two wheat brans obtained at different stages of milling, described commercially as coarse and fine wheat bran. Digestibility trials of four samples of coarse and four of fine wheat bran from four commercial Spanish firms were carried out in 90 New Zealand White×Californian rabbits fed ad libitum. Fine brans were characterised by a higher content of particles of less than 1 mm, while coarse brans had a higher content of particles greater than 2 mm. There was no significant differences in the chemical composition of the brans, but fine brans showed, on average, a significantly higher ( P<0.05) content of crude protein bound to acid-detergent fibre (2.94 vs. 1.90 g CP–ADF kg −1 dry matter). The digestibility of the chemical components did not vary widely except for crude fibre and crude protein (CP) which were, on average, significantly higher in coarse than fine bran. Animals on coarse bran consumed more feed (126.2 g/day) than those on fine bran (111.7 g/day). The best single predictor of digestible energy (DE) and gross energy digestibility (dGE) was ADF ( R 2 /R max 2 =0.81 and 0.79 , respectively; P<0.001). A significant improvement in the accuracy of prediction was obtained when CP–ADF ( P<0.01) was introduced into the model ( R 2 /R max 2=0.88 and 0.89 for DE and dGE, respectively). The best prediction for crude protein digestibility (dCP) was obtained by the inclusion in the model of both ADF and CP–ADF ( R 2/ R max 2=0.64; P<0.001). For digestible protein, the best single predictor was acid-detergent lignin ( R 2/ R max 2=0.63; P<0.001), although accuracy of digestible protein prediction was improved with crude protein and CP–ADF as independent variables ( R 2/ R max 2=0.69; P<0.001). Results suggest that the classification of wheat bran into coarse and fine brans is difficult to justify from their chemical composition and that their nutritive value seem to be related to the digestibility of its fibrous or protein fractions and less to other nutritive components.