Physical breakdown of chickweed, dandelion, dock, ribwort, spurrey and perennial ryegrass when eaten by sheep and when macerated

Journal of Agricultural Science, Cambridge (1997), 129, 419 428. 1997 Cambridge University Press Printed in the United Kingdom 419 Physical breakdown of chickweed, dandelion, dock, ribwort, spurrey and perennial ryegrass when eaten by sheep and when macerated D. WILMAN, R. W. DERRICK AND G. MOSELEY Welsh Institute of Rural Studies, University of Wales, Aberystwyth, Ceredigion SY23 3AL, UK Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Ceredigion SY23 3EB, UK (Revised MS received 12 March 1997) SUMMARY Six plant species were compared in terms of their physical breakdown when eaten by sheep and when macerated: chickweed (Stellaria media (L.) Vill.), dandelion (Taraxacum officinale Weber), dock (Rumex obtusifolius L.), ribwort (Plantago lanceolata L.), spurrey (Spergula arvensis L.) and perennial ryegrass (Lolium perenne L.). In two experiments at Aberystwyth in 1985 and 1986, the species were artificially dried and fed to lambs as the total diet. In another experiment in 1987, they were fed fresh, in 1 5 min meals, to yearling sheep. Perennial ryegrass was more difficult to break down than the dicotyledonous species, judging by the particle size distribution in macerated and in chewed material and in the rumen contents and from the rather long time the sheep spent eating and ruminating per 100 g dry matter (DM) intake and the rather high fibrosity index. The width of some of the smaller ryegrass particles in the rumen was such that they must have contained only a single vein. Spurrey was readily broken down by macerating and by chewing and a relatively short time was spent eating and ruminating per 100 g DM intake. The shape of spurrey particles in the rumen was quite similar to that of stemmy ryegrass particles and the fibrosity index of spurrey was high. The breakdown of chickweed was similar to that of spurrey, but the fibrosity index of chickweed was lower. Accumulation of DM in the caecum appeared particularly pronounced in sheep fed ribwort or dock. The dock particles in the rumen typically had a low ratio of length to width and it seemed that dock particles did not need to be reduced in size as much as ryegrass particles before passing out of the rumen. INTRODUCTION The physical breakdown of food is important in relation both to intake and to digestion. The voluntary intake of fibrous food, including forage, by ruminants can be restricted by the rate and extent of breakdown into particles small enough to pass out of the reticulorumen (Moseley & Jones 1984; Ulyatt et al. 1986). Similarly, digestibility can be restricted by lack of access by rumen microbes to blocks of thick-walled cells in incompletely broken down particles of fibrous food (Wilson & Mertens 1995). Plants which may be eaten by ruminants vary enormously in morphology and anatomy and hence are likely to vary in the ways in which they break into particles, and in the ease of breakdown, during eating and rumination. Perennial ryegrass (Lolium perenne L.), the major sown herbage species in the UK, has the advantage of being tough enough to stand up to intensive treading by grazing animals (Spedding & Diekmahns 1972), but this toughness may be a disadvantage from the point of view of providing a diet which is easy and quick to eat. Wilman & Riley (1993) compared 15 grassland species in a search for types of plant which seemed likely to be broken down easily in the mouth and rumen and which, as a result, had a high potential intake. From that study, two annual and three perennial herbaceous, dicotyledonous non-legumes were selected as being of sufficient promise and interest to be compared with perennial ryegrass in feeding experiments: chickweed (Stellaria media (L.) Vill.), common dandelion (Taraxacum officinale Weber), broad-leaved dock (Rumex obtusifolius L.), ribwort (Plantago lanceolata L.) and spurrey (Spergula arvensis L.). The intake by sheep and the digestibility of these five species and perennial ryegrass were reported by Derrick et al. (1993). As part of the same project, the extent to which the diets were broken

420 D. WILMAN, R. W. DERRICK AND G. MOSELEY down in the sheep was recorded by sieving oesophageal extrusa and the contents of the reticulorumen, omasum, abomasum and caecum and the faeces. The diets were also macerated and sieved and were tested for fibrosity and for the time the sheep spent eating and ruminating. The dimensions of particles were recorded at the reticulo-rumen stage. The objective was to identify differences between the six plant species in breakdown characteristics, as a contribution to an improved understanding of forage utilization. MATERIALS AND METHODS The sowing and management of the field plots and the three feeding experiments were described by Derrick et al. (1993). The six species were grown at Aberystwyth, using a randomized block design with two blocks, each of six plots. Experiment 1, 1985 The plots were sown at the beginning of August 1985 and harvested on 28 October 1985. The harvested crops were artificially dried on a moving bed, lowtemperature grass drier and fed ad libitum, without any supplement, to castrated male lambs (c. 32kg liveweight (LW)), in individual pens, for c. 20 days, of which the final 12 days were used for recording intake and digestibility. Immediately after this period, the lambs were slaughtered and the reticulo-rumen removed. Initially, 12 lambs were used, two per diet, in a randomized block design; later, a further four lambs were used, one fed on chickweed, two on ryegrass and one on spurrey. Fibrosity index (Hides et al. 1983) was determined by milling two 5 g samples per plot of dried crop. One 3 g sample per plot of dried crop was cut into 2 cm lengths, soaked overnight in water and macerated for 1 min in 150 ml of water in a 250 ml round-bottomed flask, using an Ultra Turrex (Janke and Kunkel) macerator which had two revolving blades surrounded by a non-revolving blade. The macerated crop was separated into fractions of different particle size using an Analysette 3 (Fritsch GMBH) wet sieve shaker with sieve mesh sizes 4, 2, 1, 0 5, 0 25 and 0 125 mm according to Moseley (1984). The wet sieve shaker was also used to separate c. 2 5 g dry weight per lamb of rumen contents into fractions of different particle size. Particles which will pass through a 1 mm sieve can be regarded as small enough to pass from the reticulo-rumen of the sheep to the omasum and abomasum (Poppi et al. 1985). Experiment 2, 1986 The plots were harvested on 23 June and 1 October 1986 and the material was artificially dried. The chickweed and spurrey plots were re-sown on 30 June 1986 and one of the ribwort plots on 9 July. Insufficient dandelion was harvested in 1986 for a feeding experiment. The dried crops of the remaining five species, cut on 1 October, together with the Junecut ryegrass, were fed ad libitum, without any supplementation, to castrated male lambs (c. 34 kg LW) in metabolism cages for c. 19 days, of which the final 9 days were used for recording digestibility, intake and time spent eating and ruminating. Thirtysix lambs were used, six per diet, in a randomized block design. All the lambs were then slaughtered; the rumen contents were recovered from the lambs of four replicates and the omasum, abomasum and caecum contents were recovered from the lambs of three of those replicates. The fibrosity index of the dried crop and the particle size distribution of the macerated crop and of the rumen contents were determined as in Expt 1. The particle size distribution of the omasum, abomasum and caecum contents was determined as for the rumen contents; the same procedure was used to estimate the particle size distribution of the faeces, except that each faeces sample was boiled for 60 min in 100 ml of neutral detergent solution before sieving, in order to break up clumps of particles which were stuck together. The time spent eating and ruminating was estimated by using a jaw balloon and pressure transducer. Experiment 3, 1987 The same species and plots were used as in Expt 1. The plots were cut and raked clear on 26 May and 20 July 1987. The chickweed and spurrey plots were re-sown on 2 July. Sufficient material was cut each morning for feeding to sheep in each of four 6-day periods, beginning on 24 August, 7 September, 21 September and 5 October. The periods species interaction (15 D.F.) was used to calculate the S.E. The fibrosity index of oven-dried crop samples was determined as in Expt 1, but using 24 samples per species. The particle size distribution of the macerated crop was determined as in Expt 1, but using 16 samples per species; each sample had been preserved by freezing and contained c. 2 5 g dry matter (DM). In each of the four 6-day periods, fresh material of each species was fed to each of two oesophagealfistulated sheep. The chewed forage was collected from the fistula in a polythene bag, within a linen bag tied round the sheep s neck. The sheep were adult castrate males (c. 54 kg LW). The particle size distribution of the chewed crop, recovered from the oesophageal fistula, was determined by sieving in one or two samples per sheep per period, using the same sieves as in Expt 1; each sample had been preserved by freezing and contained c. 2 5 g DM.

Physical breakdown of six grassland species 421 Table 1. Fibrosity index of diets and time spent by sheep eating and ruminating Ryegrass Chickweed Dandelion Dock Ribwort Spurrey Leafy Stemmy S.E. Mean Fibrosity index (5 D.F.) Experiment 1 560 590 570 530 800 740 34 630 Experiment 2 23 June 1986 harvest* 720 700 1110 1130 1730 1340 58 1120 1 October 1986 harvest* 560 330 570 810 980 540 129 630 Experiment 3 750 730 830 1440 1320 1390 60 1080 Time spent eating (minutes) (19 D.F.) Experiment 2 Per day 308 306 388 332 323 372 31 1 338 Per 100 g dry matter intake 31 7 32 6 42 4 26 5 36 7 46 3 3 10 36 0 Per 100 g cell wall intake 100 130 95 66 74 92 7 5 93 Time spent ruminating (minutes) (19 D.F.) Experiment 2 Per day 485 372 434 486 488 532 28 2 466 Per 100 g dry matter intake 50 9 40 3 47 2 39 0 57 1 67 0 4 23 50 3 Per 100 g cell wall intake 160 157 105 97 115 133 10 6 128 * Sown species only. Full records were obtained from different numbers of sheep on different diets (6 on the chickweed and stemmy ryegrass diets, 4 on spurrey and leafy ryegrass, 3 on ribwort and 2 on dock). The S.E. s listed are for comparing chickweed with spurrey; appropriate adjustment is needed for the other comparisons, e.g. to compare dock with ribwort multiply the listed S.E. by1 41.

422 D. WILMAN, R. W. DERRICK AND G. MOSELEY Table 2. Breakdown of diet into particles when macerated and when chewed by sheep Ryegrass Chickweed Dandelion Dock Ribwort Spurrey Leafy Stemmy S.E. Mean After maceration Experiment 1 (5 D.F.) (a) Dry matter retained above the 1 mm sieve 16 0 31 6 11 7 26 9 17 6 33 7 2 01 22 9 (b) Particulate dry matter below the 1 mm sieve 34 6 21 0 41 9 31 0 38 2 19 3 3 33 31 0 (c) Soluble dry matter 49 4 47 4 46 5 42 1 44 2 47 0 2 53 46 1 Experiment 2 (5 D.F.) (a) Dry matter retained above the 1 mm sieve 8 3 8 0 21 6 19 2 28 4 41 6 0 82 21 2 (b) Particulate dry matter below the 1 mm sieve 54 6 63 9 49 6 51 9 40 4 23 2 1 11 47 3 (c) Soluble dry matter 37 1 28 1 28 7 28 9 31 2 35 1 0 93 31 5 Percentage of particulate dry matter retained on 2 7 2 4 9 4 9 7 33 4 53 3 1 61 18 5 the 4 mm sieve Experiment 3 (15 D.F.) (a) Dry matter retained above the 1 mm sieve 23 5 29 5 14 7 18 8 17 2 37 1 2 01 23 5 (b) Particulate dry matter below the 1 mm sieve 41 0 39 3 52 1 45 1 51 5 33 3 2 23 43 7 (c) Soluble dry matter 35 5 31 1 33 2 36 2 31 3 29 5 2 07 32 8 Percentage of particulate dry matter retained on 9 4 9 3 9 0 11 8 8 8 47 4 2 70 15 9 the 4 mm sieve After chewing Experiment 3 (15 D.F.) (a) Dry matter retained above the 1 mm sieve 41 4 50 3 45 8 44 7 35 4 49 8 1 99 44 5 (b) Particulate dry matter below the 1 mm sieve 15 9 15 6 27 0 20 0 22 5 14 1 1 71 19 2 (c) Soluble dry matter 42 7 34 0 27 2 35 3 42 2 36 2 2 86 36 3 Percentage of particulate dry matter retained on 46 1 52 9 44 3 48 6 40 2 67 3 2 51 49 9 the 4 mm sieve

Physical breakdown of six grassland species 423 Table 3. Particulate and soluble dry matter in the rumen* of sheep and weight of rumen* contents Ryegrass Chickweed Dandelion Dock Ribwort Spurrey Leafy Stemmy S.E. Mean Experiment 1 (8 D.F.) (a) Dry matter retained above the 1 mm sieve 25 2 21 1 19 6 16 4 19 3 23 5 2 30 20 9 (b) Particulate dry matter below the 1 mm sieve 35 0 30 5 50 8 34 1 43 2 30 8 3 80 37 4 (c) Soluble dry matter 39 8 48 4 29 6 49 5 37 5 45 6 4 92 41 7 Percentage of particulate dry matter (a) On the 4 mm sieve 27 2 35 3 19 2 27 0 11 4 36 2 4 44 26 1 (b) On the 2 mm sieve 6 3 2 9 4 0 2 6 7 3 2 9 0 57 4 3 (c) On the 1 mm sieve 8 9 2 6 4 6 2 8 12 2 4 4 0 81 5 9 (d) On the 0 5 mm sieve 11 7 5 0 9 8 5 4 14 3 5 0 1 24 8 5 (e) On the 0 25 mm sieve 9 9 5 5 9 3 7 0 20 0 6 9 1 50 9 8 (f) On the 0 125 mm sieve 11 5 9 8 10 9 10 4 20 3 15 1 1 81 13 0 (g) Passing through the 0 125 mm sieve 24 6 38 8 42 2 44 8 14 8 26 4 3 46 31 9 Experiment 2 (15 D.F.) Fresh weight of rumen contents (g) 4090 4260 3860 4110 3530 4010 298 3980 Dry weight of rumen contents (g) 423 536 484 556 386 448 35 8 472 (a) Dry matter retained above the 1 mm sieve 28 2 29 3 26 7 24 5 26 0 35 2 1 78 28 3 (b) Particulate dry matter below the 1 mm sieve 47 6 52 5 58 6 53 0 44 9 47 3 2 29 50 7 (c) Soluble dry matter 24 1 18 2 14 7 22 5 29 1 17 4 2 83 21 0 Percentage of particulate dry matter (a) On the 4 mm sieve 15 0 17 1 15 7 12 8 22 8 22 8 1 69 17 7 (b) On the 2 mm sieve 10 0 9 5 7 9 8 0 7 5 9 3 1 15 8 7 (c) On the 1 mm sieve 12 2 9 1 7 5 11 0 6 6 10 4 1 00 9 5 (d) On the 0 5 mm sieve 17 8 12 5 13 1 17 0 4 0 7 6 1 14 12 0 (e) On the 0 25 mm sieve 12 0 9 5 14 2 14 9 7 1 10 4 0 83 11 4 (f) On the 0 125 mm sieve 10 2 12 1 16 1 15 3 18 3 15 9 1 41 14 6 (g) Passing through the 0 125 mm sieve 22 7 30 2 25 4 21 1 33 7 23 5 2 13 26 1 * Includes the reticulum. Rumen contents were obtained from different numbers of sheep on different diets (4 on ryegrass, 3 on chickweed and spurrey, 2 on dandelion and 1 on dock and ribwort). The S.E.s listed are for comparing chickweed with spurrey; appropriate adjustment is needed for the other comparisons, e.g. to compare dock with ribwort multiply the listed S.E. by1 73.

424 D. WILMAN, R. W. DERRICK AND G. MOSELEY RESULTS The fibrosity index (Table 1) of spurrey was consistently high (i.e. a relatively large amount of energy was required to mill the crop). The fibrosity index of chickweed and dandelion was consistently low; that of dock was intermediate; that of ribwort was low in Expt 1, but high in the other two experiments (when the crop contained more stem); that of ryegrass was high except in October 1986. The time spent eating and ruminating per 100 g DM intake and per 100 g cell wall intake in Expt 2 (Table 1) was consistently higher in stemmy (Junecut) ryegrass than in spurrey (P 0 05). The time spent eating and ruminating chickweed and dock was low in relation to DM intake, but high in relation to cell wall intake. Time spent ruminating relative to time spent eating was greater in chickweed, ryegrass and spurrey than in ribwort and dock. The plant material which was most difficult to break down by maceration or chewing was ryegrass, particularly the stemmy crop harvested in June 1986, as indicated by the higher percentage of particulate DM retained on the largest sieve used (4 mm) on the ryegrass than on any of the other diets (P 0 01) (Table 2). The greater resistance to breakdown of ryegrass compared with the dicotyledonous species was also shown by the relatively high percentage of total sample DM retained above the 1 mm sieve (that on the 1 mm sieve plus that on the 2 and 4 mm sieves). The percentage of total sample DM retained above the 1 mm sieve was high in dandelion and low in chickweed, dock and spurrey. The percentage of sample DM which was particulate DM below the 1 mm sieve was consistently higher in dock than in ryegrass (P 0 01). The percentage of sample DM which was soluble was consistently high in chickweed. Chewing by sheep did not break the diets down as much as did the maceration technique which was used; the difference between chewing and maceration was greater with the dicotyledonous species than with ryegrass and was shown particularly in the percentage of particulate DM retained on the 4 mm sieve. The greater difficulty in breaking down ryegrass compared with the dicotyledonous species was evident in the size of particles in the rumen, a relatively high percentage of rumen particulate DM being retained on the 4 mm sieve on ryegrass diets, compared in particular with spurrey (P 0 01) (Table 3). The percentage of rumen particulate DM on the 1, 0 5 and 0 25 mm sieves was lower with the leafy (October-cut) ryegrass than with the spurrey diet (P 0 01). On the other hand, the percentage of rumen particulate DM which passed through the 0 125 mm sieve was greater with leafy ryegrass than with spurrey (P 0 05). The rumen contents of the sheep fed stemmy (June-cut) ryegrass had a high percentage of total DM retained above the 1 mm sieve (that on the 1 mm sieve plus that on the 2 and 4 mm sieves) and a low percentage of soluble DM, but this was not the case with leafy (October-cut) ryegrass. The percentage of rumen contents DM made up of particles which passed through the 1 mm sieve was high on the dock diet in Expt 1 and on dock, ribwort and spurrey in Expt 2. Table 4. Dimensions of sieved particles from the rumen* of sheep in Expt 2 Ryegrass Mean length and width (mm) of S.E. sieved particles Chickweed Dock Ribwort Spurrey Leafy Stemmy (15 D.F) Mean (a) On the 1 mm sieve (i) Length 4 50 4 21 4 22 4 82 4 84 4 58 0 318 4 53 (ii) Width 1 52 2 03 1 22 1 01 0 91 0 97 0 090 1 28 (iii) Length width 2 97 2 08 3 65 5 01 5 44 4 79 0 445 3 99 (b) On the 0 5 mm sieve (i) Length 3 11 2 88 2 91 3 23 3 54 3 15 0 196 3 14 (ii) Width 0 70 1 45 0 68 0 73 0 58 0 64 0 065 0 80 (iii) Length width 4 48 2 02 4 32 4 40 6 36 4 98 0 426 4 43 (c) On the 0 25 mm sieve (i) Length 1 52 1 18 1 26 1 33 1 86 1 65 0 140 1 47 (ii) Width 0 31 0 37 0 33 0 35 0 19 0 28 0 023 0 30 (iii) Length width 4 96 3 24 3 78 3 84 10 18 6 02 0 765 5 34 (d) On the 0 125 mm sieve (i) Length 1 10 1 12 0 84 0 98 1 10 1 00 0 094 1 02 (ii) Width 0 19 0 21 0 17 0 20 0 12 0 17 0 013 0 18 (iii) Length width 6 00 5 34 5 08 5 06 9 35 5 91 0 647 6 12 * Includes the reticulum.

Physical breakdown of six grassland species 425 Table 5. Weight of contents of omasum, abomasum and caecum and particulate and soluble dry matter in omasum, abomasum, caecum and faeces in Expt 2 Ryegrass S.E. Chickweed Dock Ribwort Spurrey Leafy Stemmy (10 D.F.) Mean Dry weight of contents (g) (a) Omasum 2 5 6 8 6 4 9 5 3 4 4 3 1 01 5 5 (b) Abomasum 11 3 15 7 4 6 14 6 11 7 8 6 2 43 11 1 (c) Caecum 23 7 39 7 41 8 23 8 24 9 22 7 4 23 29 4 (a) Dry matter retained above the 1 mm sieve (i) Omasum 4 0 4 2 4 7 3 3 3 5 2 9 0 92 3 8 (ii) Abomasum 6 1 8 8 4 4 6 7 2 2 2 3 1 27 5 1 (iii) Caecum 2 0 3 6 1 8 1 3 1 2 1 3 0 48 1 9 (iv) Faeces 4 3 3 5 1 0 2 2 0 7 1 9 0 56 2 3 (b) Particulate dry matter below the 1 mm sieve (i) Omasum 76 6 66 0 78 7 71 2 62 2 73 7 4 32 71 4 (ii) Abomasum 63 7 65 6 73 0 66 3 54 5 73 0 3 46 66 0 (iii) Caecum 56 6 72 5 76 4 66 7 53 1 65 4 3 23 65 1 (iv) Faeces 42 2 41 7 55 9 52 4 37 2 54 7 1 80 47 4 (c) Soluble dry matter (i) Omasum 20 4 29 7 16 6 25 5 34 3 23 5 4 82 25 0 (ii) Abomasum 30 2 25 6 22 6 26 9 43 3 24 7 3 36 28 9 (iii) Caecum 41 4 23 8 21 8 32 0 45 6 33 3 3 27 33 0 (iv) Faeces 53 5 54 9 43 0 45 4 62 0 43 3 1 92 50 4

426 D. WILMAN, R. W. DERRICK AND G. MOSELEY The dry weight of the rumen contents was greater on the spurrey and dock diets than on leafy ryegrass or chickweed in Expt 2 (P 0 05). Plant particles in the rumen of sheep fed leafy ryegrass were typically rather long and thin (Table 4); the mean ratio of length to width was 9:1 for particles on the 0 25 and 0 125 mm sieves with the leafy ryegrass diet, a significantly wider ratio (P 0 01) than was recorded with any of the other diets. At the other extreme of particle shape were those on the 1 and 0 5 mm sieves from the rumen of sheep fed dock, with a mean ratio of length to width of 2:1. The dry weight of omasum contents was higher on the dock and spurrey than on the chickweed and leafy ryegrass diets (P 0 05); the dry weight of abomasum contents was higher on the dock and spurrey diets than on ribwort (P 0 05); and the dry weight of the caecum contents was higher on the dock and ribwort than on any of the other four diets (P 0 05) (Table 5). The percentage of total sample DM which was retained above the 1 mm sieve was low on all six Expt 2 diets in the omasum, abomasum and caecum contents and in the faeces; the percentage was higher with dock than with some of the other species, particularly in the abomasum and caecum contents. In the omasum, abomasum and caecum contents and in the faeces, the percentage of total sample DM which was in the form of particles which passed through the 1 mm sieve was higher on the ribwort than on the leafy ryegrass diet (P 0 05) and the percentage of total sample DM which was soluble was particularly high on the leafy ryegrass diet. DISCUSSION The rather high fibrosity index of perennial ryegrass, the rather long time spent eating and ruminating per 100 g DM intake, the high proportion of particulate DM retained on the largest (4 mm) sieve, after macerating the diet, after chewing the diet and in the rumen contents, all indicate plant material which is rather tough and difficult to break down, compared with the material from temperate, dicotyledonous species. A similar conclusion was reached by Wilman & Riley (1993), who recorded fibrosity and particle size distribution after maceration, and by Wilman et al. (1996), who recorded rate of intake. The conclusion is reinforced by the low numbers of chews min of chewing activity and the below average weight of DM consumed min of chewing activity in the present Expt 3 (Derrick et al. 1993). Presumably the higher proportion of cell wall in the grass than in the dicotyledonous species (Derrick et al. 1993; Wilman & Riley 1993) is one reason for the greater resistance to breakdown of the grass. Derrick et al. (1993) noted that the voluntary intake of perennial ryegrass compared with that of the dicotyledonous species was not as high as might have been predicted from the high digestibility of the ryegrass; presumably voluntary intake is limited by the slow rate of breakdown of perennial ryegrass in the mouth and rumen. The greater resistance to maceration of stemmy compared with leafy ryegrass (Table 2) did not seem to be associated with much difference in voluntary intake between stemmy and leafy ryegrass (Derrick et al. 1993); it seems likely that the sheep compensated to some extent for the greater resistance to breakdown of the stemmy material by spending rather more time eating and ruminating (Table 1). The ratio of length to width in the particles recovered from the rumen of the sheep fed leafy perennial ryegrass in Expt 2 (weighted mean over the four sieve sizes recorded 8 3) was similar to that recorded by Mtengeti et al. (1995) (8 8) in chewed, leafy perennial ryegrass, using the same cultivar, Melle, as in the present experiments. The mean width of rumen particles held on the 0 125 mm sieve (the smallest sieve used) in the case of the leafy ryegrass diet, 0 12 mm, was less than the mean distance of 0 16 mm between adjacent veins in the intact perennial ryegrass leaf blades examined by Mtengeti et al. (1995), suggesting that ryegrass tissue can be reduced to single vein width if it receives enough chewing and stays in the rumen long enough. Many of the particles in the rumen appeared small enough to pass out of the rumen readily (as noted with grass diets by Poppi et al. 1981) and yet had been retained; their retention would presumably contribute to rumen-fill and hence restrict intake, but retention would presumably have the advantage of enhancing digestibility. Retention in the rumen may have been partly due to the long, thread-like ryegrass particles creating a matted structure which trapped some of the small particles, making it more difficult for the latter to move through the rumen contents into a position from which they might be presented for passage through the reticuloomasal orifice, as suggested by Moseley (1982) and Moseley & Jones (1984), when considering a comparison of perennial ryegrass with white clover. Even small particles are likely to contain blocks of tightly packed, thick-walled cells to which rumen microbes have only limited access (Wilson & Mertens 1995). Particles such as those on the 0 25 mm sieve from the rumen contents of sheep fed leafy ryegrass (which were 1 86 mm long and 0 19 mm wide on average) may contain 400 tightly packed, thick-walled cells (Fig. 5 of Wilson & Mertens (1995)). The high fibrosity index of spurrey might suggest plant material which is difficult to break down, leading to restricted intake (Chenost 1966). However, the voluntary intake of spurrey appears to be particularly high (recorded in Expts 1 and 2 of Derrick et al. (1993)), as does the rate of intake (Expt 3 of Derrick et al. (1993), Mtengeti et al. 1995; Wilman et al. 1996), showing that, when comparing

Physical breakdown of six grassland species 427 plant species of very different structure and morphology, recording fibrosity may be of limited value as a predictor of intake. Similarly, the suggestion of Troelsen & Campbell (1968) that plant species which break down into short, broad particles (lucerne in their case) are likely to have a higher voluntary intake than species which break into longer, thinner, more fibre-like particles (grasses in their case) is of doubtful value when a comparison involves a species such as spurrey; the particles of spurrey from the rumen which were measured in the present Expt 2 (Table 4) were similar in length and width to those derived from stemmy ryegrass, although the voluntary intake of spurrey was much higher than that of stemmy ryegrass (Derrick et al. 1993). Measures which did indicate the greater potential voluntary intake of spurrey than of perennial ryegrass were the greater breakdown of spurrey when macerated (Table 2 and Wilman & Riley (1993)) and when chewed (Table 2), the shorter time spent eating and ruminating spurrey per 100 g DM intake (Table 1) and the smaller proportion of large particles in the rumen of sheep on the spurrey diet (Table 3). Evidently spurrey, despite a rather high proportion of cell wall (as indicated by neutral detergent fibre, Derrick et al. (1993)) and a high fibrosity index, breaks down readily when eaten by sheep and is extremely palatable (as was noted many years ago by Fream (1900)). The other annual species examined, chickweed, broke down to a similar extent to spurrey when macerated (Table 2 and Wilman & Riley (1993)) and was fairly similar to spurrey in particle size distribution in the rumen, omasum and abomasum (Tables 3 and 5) and in the length and width of rumen particles (Table 4) and had a lower fibrosity index than spurrey. However, the voluntary intake and rate of intake of chickweed were appreciably lower than that of spurrey (Derrick et al. 1993). The chickweed appeared less palatable than spurrey and was perhaps less suitable as a food for sheep, as indicated by its higher K and lower Na concentration (Wilman & Derrick 1994), the greater weight of urine produced when it was fed (Wilman & Derrick 1994) and the solid, rather slimy nature of the rumen contents of sheep which had been fed chickweed. Dandelion was typical of the dicotyledonous species in breaking down more readily than perennial ryegrass when macerated or chewed (Table 2) and having a lower cell wall content than perennial ryegrass (Derrick et al. 1993; Wilman & Riley 1993). Dandelion also had a lower fibrosity index than perennial ryegrass (Table 1 and Wilman & Riley (1993)). It appears to be a palatable species, at least at the vegetative stage (Marten et al. 1987), with fairly high voluntary intake and rate of intake (Derrick et al. 1993). Ribwort also broke down more readily than perennial ryegrass when macerated or chewed (Table 2) and it had a lower cell wall content than perennial ryegrass (Derrick et al. 1993; Wilman & Riley 1993). Its leaf had a lower fibrosity index than perennial ryegrass leaf (Expt 1 and Wilman & Riley (1993)), but when the crop was stemmy (Expts 2 and 3) the fibrosity was rather high. A particularly high proportion of the DM in the omasum, abomasum, caecum and faeces of sheep fed ribwort was in the form of particles sufficiently small to pass through a 1 mm sieve, suggesting thorough breakdown in the mouth and rumen. The digestibility of the cell wall fraction of stemmy crops of ribwort was particularly low (Derrick et al. 1993), which could be a reason for the accumulation of DM in the caecum of sheep fed stemmy ribwort (Table 5). The following features of dock suggest that its voluntary intake and rate of intake might be high: ready breakdown during maceration (Table 2 and Wilman & Riley (1993)) or chewing (Table 2), a preponderance of small particles in the rumen (Table 3), particles with a low ratio of length to width (Table 4) and a low cell wall content (Derrick et al. 1993; Wilman & Riley 1993). The voluntary intake of dried dock was at least as high as that of leafy and stemmy ryegrass, chickweed and ribwort in Expt 2 of Derrick et al. (1993), but the rate of intake of the fresh crop, particularly when chopped, was low, presumably because of taste and or smell (Derrick et al. 1993). It appears from the present results that sheep may spend less time ruminating when fed dock rather than some other species and that a dock diet does not need to be broken down into quite such small particles before passing out of the rumen. However, perhaps partly because of the larger particles and the incomplete digestion which they represent, there may be some accumulation of material in the caecum. CHENOST, M. (1966). Fibrousness of forages: its determination and its relation to feeding value. In Proceedings of the Xth International Grassland Congress, Helsinki, 1966, pp. 406 411. Helsinki: Finnish Grassland Association. REFERENCES DERRICK, R. W., MOSELEY, G.& WILMAN, D. (1993). Intake, by sheep, and digestibility of chickweed, dandelion, dock, ribwort and spurrey, compared with perennial ryegrass. Journal of Agricultural Science, Cambridge 120, 51 61. FREAM, W. (1900). The Complete Grazier and Farmers and

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