Biological and chemical assessment of feed proteins before and after rumen exposure

Abstract

Samples of six concentrate feedstuffs (soya-bean meal, sunflower meal, fish meal, maize gluten meal, cottonseed cake and linseed cake) were incubated in the rumens of four mature cows for 14 h. The residues and non-incubated feedstuffs were used to make 12 diets for a biological assay in golden hamsters. The intestinal digestibility of the feed samples and residues was determined with a mobile nylon bag technique. Samples were also analysed for their amino acid content to calculate essential amino acid indexes for milk and meat. The biological value (BV) measured in hamsters varied with feed and rumen exposure (feed × incubation effect P < 0.01). The correlations between hamster BV and essential amino acid index (EAAI) were significant but low (0.64 and 0.65 for milk and meat respectively, P < 0.05). Nitrogen digestibility was significantly ( P < 0.001) lower in the hamsters than in the mobile bags. The amino acid profiles of the six feeds before and after rumen incubation varied only slightly and the EAAI was not affected by rumen exposure. The golden hamster cannot be considered an adequate model animal for determining post rumen digestibility and BV but it does provide a useful comparative indicator for the changes which feeds undergo in the rumen.