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Evidence in support of a role for plant-mediated proteolysis in the rumens of grazing animals

Published online by Cambridge University Press:  08 March 2007

A. H. Kingston-Smith*
Affiliation:
Department of Plant, Animal and Microbial Science, Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth SY23 3EB, UK
R. J. Merry
Affiliation:
Department of Plant, Animal and Microbial Science, Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth SY23 3EB, UK
D. K. Leemans
Affiliation:
Department of Plant, Animal and Microbial Science, Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth SY23 3EB, UK
H. Thomas
Affiliation:
Department of Plant, Animal and Microbial Science, Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth SY23 3EB, UK
M. K. Theodorou
Affiliation:
Department of Plant, Animal and Microbial Science, Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth SY23 3EB, UK
*
*Corresponding author: Dr A. H. Kingston-Smith, fax +44 (0) 1970 828357, email alison.kingston-smith@bbsrc.ac.uk
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Abstract

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The present work aimed to differentiate between proteolytic activities of plants and micro-organisms during the incubation of grass in cattle rumens. Freshly cut ryegrass was placed in bags of varying permeability and incubated for 16 h in the rumens of dairy cows that had previously grazed a ryegrass sward, supplemented with 4 kg dairy concentrate daily. Woven polyester bags (50 μm pore size) permitted direct access of the micro-organisms and rumen fluid enzymes to the plant material. The polythene was impermeable even to small molecules such as NH3. Dialysis tubing excluded micro-organisms and rumen enzymes/metabolites larger than 10 kDa. DM loss was 46·3 % in polyester, 36·2 % in polythene and 38·1 % in dialysis treatments. It is possible that the DM loss within polythene bags occurred due to a solubilisation of plant constituents (e.g. water-soluble carbohydrates) rather than microbial attachment/degradation processes. The final protein content of the herbage residues was not significantly different between treatments. Regardless of bag permeability, over 97 % of the initial protein content was lost during incubations in situ. Electrophoretic separation showed that Rubisco was extensively degraded in herbage residues whereas the membrane-associated, light-harvesting protein remained relatively undegraded. Protease activity was detected in herbage residues and bathing liquids after all incubation in situ treatments. Although rumen fluid contains proteases (possibly of plant and microbial origin), our results suggest that, owing to cell compartmentation, their activity against the proteins of intact plant cells is limited, supporting the view that plant proteases are involved in the degradation of proteins in freshly ingested herbage.

Information

Type
Research Article
Copyright
Copyright © The Nutrition Society 2005