Thirteen tropical and 11 temperate grasses were grown in controlled environment under daylnight temperatures of 21/13, 27/19 and 32124°C. Neutral detergent fibre (NDF) was prepared from the fifth leaf on the main stem of each plant, 2 days after it had reached maximum length. Panicum maximum var. trichoglume (tropical) and Loliumperenne cv. S24 (temperate) were also harvested at 4,8, and 12 days after this stage of development. For the tropical grasses NDF values, corrected for starch and protein, decreased with increasing growth temperature, whereas in the temperate species they increased. In the tropical group the decrease in NDF was due to a lower cellulose content, whereas hemicellulose and lignin levels generally tended to increase slightly with increasing temperature. In the temperate grasses, lignin, hemicellulose and cellulose levels all showed a consistent increase with growth temperature. At each growth temperature the lignin content of the species in the tropical group had a significant negative correlation with in vitro digestibility, and lignin appeared to be more closely associated with hemicellulose than with cellulose. In contrast, at each temperature, variation in digestibility between species of the temperate group was not correlated with lignin. Levels of cell wall components in the later-harvested material from Lolium varied in a similar manner to that of the younger growth stage, whereas older Panicum cell wall constituents showed more variability.

A tropical and a temperate grass (S. splendida and L. perenne cv. Kangaroo Valley respectively) were cut at a young stage of regrowth and fed to sheep in pens. Although the fresh plants were chemically very similar, the apparent digestibility of the S. splendida (61'4%) was much lower than that of the ryegrass (76'1 %). Analyses of the faeces showed that the hemicellulose and cellulose in each grass were digested to a similar extent, but between species, the cell-wall polysaccharides of ryegrass were digested to a much greater extent than those of S. splendida (c. 79 and 49% respectively). Notable differences between the grasses were the hemicellulose A content of the faeces from sheep fed S. splendida, which was greater than that present in the fresh plant material, and the ryegrass hemicellulose B, which had a much higher arabinose content than that of S. splendida. Glucose and galactose, which were present in the fresh plant hemicelluloses, were absent in the faeces. The differences in apparent digestibility between the two grasses could not be explained in terms of their cell-wall polysaccharide content, but resulted from differential digestion of both the hemicellulose and cellulose of each species.