The effect of supplementation with protein, energy and L-methionine, on the digestion of silage by sheep

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Abstract
Summary: Mature Romney wethers with rumen cannulae and re-entrant cannulae in the proximal duodenum were fed a basal diet of silage with supplements of formaldehydetreated casein (protein) and starch/sucrose (energy). In addition methionine availability was increased by infusion of L-methionine into the duodenum.Maximum intake was limited to near-maintenance with the aim of comparing treatment effects at the same level of intake. In practice, intake of the control silage alone decreased markedly after 10 days of feeding. This decline was significantly (P &0·01) reduced on the protein and energy supplemented diets, and intake increased again during the period of methionine infusion.Protein and energy supplementation increased the flow of total N (P < 0·01) into the duodenum on the control silage and the flow of amino acids into the duodenum was increased from 50 g/day on the basal diet, to 77 g/day on the energy-supplemented diet, and 111 g/day on the protein-supplemented diet.The percentage of amino acid N in the total N entering the duodenum was also increased by supplementation: from 72% on the control to 81% with energy supplement and 94% with protein supplement.Comparisons of the amino acid composition of duodenal digesta indicated that a substantial part of the increased duodenal protein flow on protein-supplemented silage was due to the formaldehyde-casein being protected from degradation within the rumen.The flow of amino acids into the duodenum was found to be closely related to amino acid intake, such that 67% of the variation in duodenal amino acid flow was associated with variation in intake.