The diurnal variations in the specific activities of polysaccharide-degrading enzymes after feeding were monitored in adherent and non-adherent microbial populations separated from bovine rumen liquor and digesta solids. There were marked differences in the activity profiles of the enzymes within the subpopulations. Enzymes involved in the degradation of soluble carbohydrates were more active in the non-adherent populations, and in the liquor phase subpopulation activities increased in the 1-2 h post-feed period. The muralytic enzymes were most active in the adherent population. Specific activities increased by up to 20-fold over the 24 h period, with an initial five-fold increase occurring between 8 h and 12 h after feeding. Enzyme levels in the three non-adherent populations were similar at the end of the postprandial period. In the population recovered from the liquid associated with the digesta particles, however, the activities did not increase until the latter stages of the period, whereas in the non-adherent population from the digesta solids the activities varied little during the diurnal cycle. The numbers of micro-organisms associated with the digesta solids were similar at 2 h and 20 h after feeding; the variations in enzyme levels did not occur as a result of a population increase but were due to increased activities in an established population. The plant cell wall structural polysaccharides were degraded at different rates. There was no appreciable cellulose digestion during the first 8 h of the postprandial period and although hemicellulosic constituents were removed continuously the rate of loss of both polymers was increased in the later stages of the diurnal cycle when enzyme activities were maximal.

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Selected herbage samples from a 6-year experiment in which nitrogen rates between 0 and 897 kg/ha were applied annually on perennial ryegrass swards were analysed for nitrate-nitrogen, true-protein and non-protein nitrogen, water-soluble carbohydrate, potassium and sodium content and for amino acid composition. The nitratenitrogen content of the herbage increased with increasing nitrogen rate from 224 kg/ha upwards, but the potentially toxic level of 220 mg/100 g dry matter was not reached until the annual nitrogen rate was about 560 kg/ha. On average, at the 897 kg nitrogen/ ha rate the non-protein nitrogen content had increased to 27-5 % of the total nitrogen yield, and 40-3 % of the non-protein nitrogen yield consisted of nitrate nitrogen. Nitrate content was shown to be a sensitive indicator of the level of nitrogen nutrition of the herbage, the optimum nitrogen rate for dry-matter production coinciding with a nitrate-nitrogen content of approximately 100 mg/100 g dry matter. The amino acid composition of the herbage varied little with either the rate of nitrogen or the date of cutting. It was demonstrated that, on average, a 1 % unit increase in the crude-protein content of the herbage was accompanied by a 1 % unit decrease in the carbohydrate content. The sodium content of the herbage increased with increasing nitrogen rate up to between 448 and 560 kg/ha, but the potassium content showed little variation. INTRODUCTIONs t a g e o f 8 r o w t h o n e a c h occasion > and t h e yields of herbage dry matter and crude protein were deterThe yield results have been reported (Reid, 1970(Reid, , mined. 1972) for a 6-year experiment designed to obtain Herbage samples were analysed for nitratedetailed information on the response curves relating nitrogen, water-soluble carbohydrate, potassium herbage dry-matter and crude-protein yields to and sodium content from all replicates of nine nitrogen application rate on perennial ryegrass nitrogen treatments (0, 112...897 kg nitrogen/ha) swards with and without white clover. To supple-on both the grass and clover and the pure-grass ment this information selected herbage samples swards at all cuts in the first, third and sixth years, from the experiment were analysed for nitrate-True-protein and non-protein nitrogen analyses nitrogen, true protein and non-protein nitrogen,' were made on samples from all replicates of five water-soluble carbohydrate, potassium and sodium nitrogen treatments (0, 224...897 kg nitrogen/ha) content, and amino acid composition.on the pure-grass sward only at all cuts in the 3 EXPERIMENTAL PROCEDURE y e a r S ' ^nd amino-acid analyses on samples from one replicate of the same five nitrogen treatments The treatments, design and methods were de-on the pure-grass sward at all cuts in the third year scribed in an earlier paper (Reid, 1970). Briefly, a only. series of 21 nitrogen rates ranging from 0 to For the nitrate-nitrogen analysis 1 g of dried 897 kg/ha was applied in five equal dressings each sample was extracted with 80 ml boiling water for yea...

Polysaccharide depolymerase and glycoside hydrolase enzymes involved in the degradation ofplant structural polysaccharides were most active in the adherent particle-associated microorganisms, whereas soluble saccharides were metabolized by the liquid phase and nonadherent populations. The activities were constant confirming the stability of the populations.Key words: Polysaccharidase, glycosidase, particle-associated microorganisms Although the complexity of the microbial populations associated with the particulate material in rumen digesta has been revealed by electron microscopy there is little information available on their metabolic activities. Williams and Strachan (1984) demonstrated that enzymes which degraded plant cell wall structural polysaccharides were higher in the particle-associated populations. In order to assess the constancy of digesta colonization further studies were undertaken to monitor variations in the activities of the degradative enzymes in the liquid phase and particle-associated populations from the bovlne rumen ecosystem.The microbial populations were prepared using the procedures described previously (Wil- Fig. 1 This study confirmed that plant cell wall polysaccharide-degrading enzymes were more active in the particle-associated subpopulations, 30

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