Experiments were conducted in 1967 and 1968 in which Hereford X Friesian (Experiment 1) and Friesian (Experiment 2) steer calves horn in AprO were turned out to graze at one week or 3 months of age, respectively, and maintained at three stocking densities in the ratio 1:2:3 animals per unit area. The calves grazed paddocks of S23 perennial ryegrass in rotation, and were moved when the height of grazed stuhhle at the medium stocking density was reduced to 8 cm. The rate of liveweight gain and herhage intake per head declined as stocking rate increased. When the results of the two experiments were compared, the weight gain of the calves was more closely related to the weight of herhage residues than to the height of the grazed sward. The rate of liveweight gain was depressed when the amount of herhage left after grazing fell helow 2000-2500 kg OM/ha (1800-2250 lh/ac).

1.A primary growth crop of peren;iial ryegrass (Lolium perenne L., cv. S23) was partially wilted and ensiled after the application of either formic acid-water (1:3, w/v; 7.1 I/t fresh herbage; control diet C) or formic acid-formaldehyde (1 : I, w/w; 8.8 l/t fresh herbage; formaldehyde treated diet F) which supplied 50 g HCHO/kg crude protein (nitrogen (N) x 6.25). Thc two silages were fed separately and a third diet comprising formaldehydetreated silage, supplemented with urea (20g/kg dry matter DM) at the time of feeding was also examined (diet FU).2. The three diets were fed at a level of 16 g DM/kg live weight to six 3-to six-month-old cattle fitted with rumen and re-entrant duodenal cannuks in two 3 x 3 Latin Square experiments, and measurements were made of the digestion of energy, carbohydratz and N.3. The formaldehyde-treated silage had a lower content of fermentation acids and ammonia-N, and a higher content of water-soluble carbohydrate and total amino acids. The apparent digestibility of organic matter, energy and N were depressed (P < 0.05. P < 0.05 and P < 0.01 respectively) by treatment with formaldehyde, but cellulose and neutral-detergent fibre digestibility were unaffected.4. Within the rumen the digestior. of organic matter, cellulose and neutral-detergent fibre were unaffected by formaldehyde treatment or supplemmmtation with urea. Microbial protein synthesis in the rumen was similar for the three diets (average 131 g/kg apparently digested organic matter in the rumen). 5.The application of formic acid-formaldehyde increased (P i 0.05) the amount of food protein escaping degradation in the rumen (4.76 diet C, 6.89 diet F; 7-07 diet FU g/kg protein intake). The contribution of amino acids of dietary origin at the duodenum increased (P < 0.05) from 50 (diet C) to 80 (diet F) and 82 (diet FU) g/kg DM intake, and the flow of total amino acids at the duodenum was 33% higher (P < O W I ) in cattle fed formic acid-formaldehyde silage ditts compared with the control silage due to the reduction in degradation of protein at ensiling and in the rumen.During silage fermentation, extensive proteolysis occurs with the final silage having a protein of high solubility whilst the non-protein-nitrogen can be as much as 60% of the total N. Formaldehyde has been used to protect protein from degradation in the rumen Siddons et al. 1979) of silage fed to sheep has previously been studied. In the present paper quantitative measurements were made of the digestion by cattle of the protein and energy in grass silage conserved with formic acid and with formic acid plus formaldehyde. In addition, a third diet comprising the formaldehyde-treated silage supplemented with urea at the time of feeding was studied, in order to examine what effect extra non-protein-N may have on microbial and total protein flow to the small intestine, should N supply to the microbes in the rumen be limited when formaldehyde-treated silage is fed (Beever et al. 1977).

SUMMARY1. The primary growth of a sward of S24 perennial ryegrass was harvested between 23 April and 9 May 1968, artificially dried and either chopped or coarsely milled. The two physical forms of grass were wafered either alone or together with 50% by dry weight of rolled, anaerobically stored barley, and given to 7-month-old, Hereford × British Friesian steers in an experiment of 2 × 2 factorial design.2. A representative group of animals was slaughtered at the beginning of the experiment, and the remainder were individually fed ad libitum for 70 days, after which they also were slaughtered. During the feeding period digestibility was determined by total faecal collection from all the animals individually on two occasions.3. Dry-matter intake and live-weight gain were similar on all feeds. The weight of gut contents as a percentage of final live weight was significantly lower and the carcass-weight gain was significantly higher for animals given wafers containing barley compared with those for animals given wafers of grass alone.4. Coarse milling compared with chopping reduced the apparent digestibility of dry matter, organic matter, cellulose and energy; the addition of barley increased the digestibility of organic matter but further reduced that of cellulose.5. The efficiency of conversion of digested energy to empty-weight or carcass gain was similar for wafers containing the two forms of forage, but the digested energy of wafers containing barley was converted to carcass weight with significantly greater efficiency than that of wafers consisting solely of grass.6. Physical separation of the tissues of sample joints failed to show any significant differences in the proportion of fat, muscle and bone as a result of either differences in physical form or the inclusion of barley.7. The results indicate that live-weight gain is an insufficiently sensitive measurement by which to assess the true productive potential of feeds given to ruminants in short-term experiments.

Perennial ryegrass cv. S23 was preserved by fermentation (Q, or with the addition of 8 7 1 formalin (35% w/w formaldehyde) per t fresh herbage (F) or of 9-0 1 equal mixture (by vol.) of formalin and formic acid (85% w/w solution) per t fresh herbage (FF). These three silages comprised the treatments in a three-period, crossover design in which urea (u) was given at the rate of 20 g per kg dietary DM to half the animals. Twelve calves were allocated to the treatment sequences when they were approximately 12 weeks of age from within groups which had previously received diets with or without urea.Calves ate significantly (i'<0001) less of silages F or FF than of silage C when each was offered alone, but when urea was given, intakes of silages F and FF were significantly (P < 0-001) increased such that the intakes of all three silages with urea were similar (23-6, 19-6, 19-3, 24-2, 24-2, 24-7 ±0-51 g DM per kg LW for C, F, FF, Cu, Fu and FFu, respectively). Significantly (i'<0-01) more of the DM in silage C was digested than in F or FF and the addition of urea significantly (P<0-05) increased the digestibility of DM from silage FF only F, FF, Cu, Fu and FFu, respectively). When the silages were given alone, calves spent longer eating and ruminating per kg DM ingested with F or FF than with C. The time spent on F and FF was

Wafers of dried grass which differed in particle size (modulus of fineness) were prepared and fed ad libitum to cattle and sheep. The response of the two classes of stock to the feeds was similar. The digestibility of organic matter and of cellulose decreased with decrease in modulus of fineness (more fine particles) and this was associated with more rapid passage of the finely-milled material through the alimentary tract. Organic matter intake generally increased with decrease in modulus of fineness, but the pattern of response differed between experiments. In one experiment the difference in voluntary intake between feeds with modulus of fineness of 2-5 and 1-0 was less than 5% and not significant, but in a second experiment the intake of feed with modulus of fineness of 2-1 was 18 % lower than that of feed with modulus of fineness of 1 -0. In the first experiment the wafers broke down during handling and feeding with the result that the feed of low modulus of fineness was extremely dusty, but in the second experiment a binding agent was included and little breakdown of wafers occurred. It is suggested that dustiness may have restricted the intake of some of the feeds in the first experiment. Intakes of digestible organic matter did not differ significantly between treatments in either experiment.