The nutritive values of feed proteins and feed protein residues resistant to degradation by rumen microorganisms

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Abstract
Fishmeal (FM), meat and bone meal (MBM) and rapeseed meal (RSM) were incubated for 8h (RSM) or 24 h (FM, MBM) in nylon bags in the rumens of cattle, in order to prepare from each meal sufficient residues resistant to rumen degradation for evaluation of their nutritive value. The nitrogen (N) and organic matter (OM) contents of FM and MBM were significantly (P<0.05) reduced by rumen incubation. The modified acid detergent fibre content of RSM was increased, and only traces of glucosinolates remained after rumen incubation. The amino acid profiles of FM and RSM were observed to change as a result of rumen incubation, whereas that of MBM was unchanged. The true N digestibilities of all three protein meals when fed to rats as the sole protein source were significantly (P<0.05) reduced by prior rumen incubation (FM, 0.90 to 0.86; MBM, 0.81 to 0.55 and RSM, 0.76 to 0.67). When measured using a rat bioassay, the biological values of FM (65.0 to 79.2) and RSM (53.3 to 83.1) protein were significantly (P<0.05) increased as a result of rumen incubation but that of MBM was unchanged (47.7 vs 41.1). The N digestibility of the protein meals and of their residues resistant to rumen degradation were also estimated in cattle. Samples of the feedstuffs were placed in small polyester bags, inserted into the proximal duodenum of cattle, recovered in faeces and N disappearance from the bags measured. This technique ranked the N digestibilities of the feedstuffs in the same order as in the rat.