Plant structure in relation to ease of physical breakdown in the mouth and rumen

Thesis

Grassland species were grown in the field and glasshouse and research was carried out for two years to investigate plant vascular structure in relation to physical breakdown in the mouth and rumen. Plant part morphology, vascular structural proportion and arrangement, fresh plant diet eating rate by sheep and particle breakdown characteristics were recorded. Anatomical differences, especially vascular tissue arrangement, appeared to be a major cause of the differences in intake rate between legumes and grasses. Four legumes did not differ significantly in terms of intake rate but differed significantly in terms of the proportion of vascular tissues, neutral detergent fibre content and digestibility. Tropical grasses had a higher proportion of vascular tissues, higher neutral detergent fibre content, lower digestibility, lower intake rate and were chewed into smaller particles than temperate grasses. Legumes were eaten faster and had larger particles after chewing than grasses. Legume and grass particles had a similar number of perforations or ruptures per particle. Legume leaf petiole and stem particles were longer than leaflet particles and increased the overall mean particle length of the chewed material. Petioles and stems are, therefore, important in legume particle size reduction in the mouth and rumen. Regardless of grass species, the veins of the leaf sheaths were more widely spaced than those in leaf blades, but the two plant parts were chewed to a similar particle size. Despite having a high proportion of stem and neutral detergent fibre, lucerne and spurrey were eaten quickly, showing the advantage, in respect of intake rate, of having thin pliable and/or fragile stems. The results of the present project indicate that the physical structure of plants, especially the arrangement of the vascular tissue, and plant morphology have great influence on the physical breakdown of the plants in the mouth and rumen.

NORAD (The Norwegian Agency for Development Co-operation)