Massey Documents by Type
Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294
Browse
10 results
Search Results
Item A study of the growth form and behaviour of Yorkshire fog (Holcus lanatus) and of its dry matter production compared with perennial rye-grass (Lolium perenne), both with and without fertilizers : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey Agricultural College, University of New Zealand(Massey University, 1957) Basnyat, Netre BahadurNew Zealand is a land of pastures and the greatest reliance is placed on them by farmers for the maintenance of their live-stock, which is the main source of national income. She is favoured by an equable climate and well distributed rainfall, which tends to keep her predominantly a grassland country. Every farmer should accept the aim expressed by Swift (1) to make "Two blades of grass to grow upon a spot of ground where only one grew before". Hill country pasture development is of paramount importance in New Zealand and must be extended if we are to maintain the present standard of living of an increasing population. Calder (2) said that farm production must increase greatly in the next 20 years. "We will have three-million people for when we must provide not only food, but also additional overseas exchange to maintain the standard of living of increasing population." High pasture production can only be maintained if suitable species of grasses are grown according to the soil fertility gradient. It is not uncommon for the high producing pasture species to lose their producing power where fertility falls below a certain level or where practices inimical to their best growth are followed. [From Introduction]Item A comparative study of defoliation in Holcus lantanus and Lolium perenne pastures grazed by sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master in Agriculture at Massey University(Massey University, 1993) Hu, YankaiObjectives of this study were (i) to extend limited information on the assessment of relative defoliation of grass and legume components in mixed ryegrass/white clover and yorkshire fog/white clover pastures, (ii) to test whether the balance of preference between ryegrass and clover differed from that between yorkshire fog and clover, and (iii) to compare the behaviour and the potential reaction of the two grass species under grazing conditions. Observations were made on plots of ryegrass/white clover and yorkshire fog/white clover grazed by sheep at high (12% live weight) and medium (6% live weight) herbage allowance. There were four replicates of each treatment, which were grazed in rotation over a four week period. Detailed sward measurements were made before and after grazing. Measurement of herbage mass, sward height, sward components, pasture structure and defoliation are reported. Sward surface heights were very similar for the two swards both before and after grazing. The sown grasses formed the dominant proportions in both swards, while white clover proportions were similar. The proportion of dead material was higher for yorkshire fog/white clover pasture than ryegrass/white clover pasture both before and after grazing. Tiller populations were higher for yorkshire fog than ryegrass (10355 vs. 6505 ±919 m·2). Mean stem length was greater for yorkshire fog than ryegrass (62.3 vs.35.0 ±2.8 mm), and the distribution of stem length showed a stronger positive skew. Yorkshire fog had a shorter leaf length than ryegrass. The population density of white clover nodes was similar in the two swards. White clover nodes in the two swards were quite similar in leaf weight, number and area both before and after grazing. The defoliated heights for clover in ryegrass/white clover and yorkshire fog/white clover swards (3 cm and 5 cm respectively) were similar at both low and high grazing allowance. The proportion of grass in the grazed stratum was higher for ryegrass than for yorkshire fog pasture before grazing, but the proportion of white clover was lower. Three parameters estimated from pre- and post-grazing measurements on individual grass tillers and clover nodes were used in the interpretation of pasture defoliation: namely defoliation frequency, defoliation severity and defoliation pressure (frequency x severity). In ryegrass/white clover pastures, the defoliation of leaf was significantly higher for ryegrass than white clover for all three parameters. In the comparison within yorkshire fog/white clover pastures, the defoliation frequency was not different between grass and clover, but the severity of defoliation and defoliation pressure were significantly higher for grass than clover. Ryegrass stem was grazed more severely than white clover petiole in ryegrass/white clover pastures. Defoliation parameters for yorkshire fog stems and white clover petioles in yorkshire fog/white clover pastures showed smaller and not significant differences. There was a highly significant effect of allowance on leaf defoliation in ryegrass/white clover pastures, but the effect was less marked in yorkshire fog/white clover pastures. More ryegrass leaf was grazed per day than yorkshire fog leaf. The proportion of leaf removed and the pressure of defoliation were higher in ryegrass than in fog. When white clovers were compared between the two swards, there were no differences in any of the three defoliation parameters. Leaf defoliation effects were greater at medium allowance than at high allowance. For all parameters, allowance effects were greater for grass than clover. The fact that grasses were defoliated more severely than the companion clovers in both swards reflected the effects of vertical distribution of sward components. However, the much lower defoliated height for clovers in both swards strongly suggested that sheep actively selected clover in the mixed swards despite the fact that clover was distributed much lower in the sward canopies. The greater defoliation of ryegrass than yorkshire fog leaf was attributed to greater preference of the animal for ryegrass than yorkshire fog in comparison with the companion clover.Item Genotypic variability in Yorkshire fog grass (Holcus lanatus L.) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Agronomy at Massey University(Massey University, 1990) Thuantavee, MuangthongPlant to plant genotypic variation in New-Zealand Yorkshire-Fog grass was examined in order to quantify the relative importance of average gene effects, dominance, epistasis and environment. The plant variability was contrasted also against topodeme variation. Plants were grown under glasshouse conditions (20° - 25°C), using vernalization and sixteen hour daylight to encourage growth and flowering. The confounding effect of bench position was removed by regression adjustment. Fifty half-sib lines representing ten diverse New Zealand topodemes were examined in a one-way mating design, laid out as a randomized complete block experiment. In general, half-sib and plant variances were much larger than the topodeme variance. This supports earlier findings that there are no major topodeme differences in New Zealand Yorkshire Fog grass germplasm. The broad-sense heritability estimates which indicated total genotypic contribution varied from low to high. Most botanical, flowering and tillering characters had medium to high values while the agronomic characters had medium to low estimates. The attributes with medium to high narrow-sense heritability are several measures of leaf size, tiller development, purple colour, plant height and erectness, flavanols and panicle width. Breeding methods, such as mass selection, line selection, line breeding or simple recurrent selection should ,therefore, be appropriate for these. The attributes with medium to high heterotic-sense heritability are leaf tensile strength, leaf hairiness, old disease, flowering period, panicle length and compactness and several aspects of tiller production. Breeding methods, such as recurrent selection with progeny testing or top cross progeny tests for high specific combining ability should be useful, including synthetic cultivars and some kinds of recurrent bulks. Of particular interest was the finding that there was more genetic variability for the duration of tillering and flowering periods than for tiller numbers or flower initiation. There was also evidence that the genetic activity controlling tiller number changed as the tillers aged.Item A study in the breeding and selection of Yorkshire Fog (Holcus lanatus L.) for hill land conditions in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of M. Agric. Sci.(Massey University, 1961) Munro, James M MIn a few simple words, written many years ago, we see the objectives which have become fundamental not only to the foundation of New Zealand's farming industry but to the whole economic wellbeing of the nation. In no other country has continued economic survival become so closely associated with pasture development and the progress of grassland and animal research. Since these words were first written, New Zealand has entered into an era of achievement, an ere in which the vision has come near to reality. Few new areas have been cleared of their native vegetation end the achievement has been realized by the checking of reversion and the increasing of production on the existing land. In little over thirty years, the total animal production from New Zealand's grassland has almost doubled, yet this accomplishment provides little room complacency since the future of' the nation depends on the continuation and even acceleration of this rate of progress. [From Introduction]Item Extraction and structural study of hemicellulose B from Yorkshire fog (Holcus lanatus) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University(Massey University, 1970) Lee, Kim Nyuk1.1 : Hemicellulose The structural carbohydrates are mixtures of polysaccharides which together with lignin, constitute the cell wall. Usually they are divided into three fractions: pectic substances, hemicellulose and cellulose. 1 Pectins, widely distributed in land plants are characterised by a main chain of 1-4 linked galacturonic acid units. They may also contain rhamnose, galactose, xylose, arabinose and fucose in varying amounts. These sugars form part of the main chain in some pectins and branch chains in others. 2 Cellulose is generally present in the plant cell as aggregates of fibrils or partly crystalline bundles. They consist of parallel chains of ß 1-4 linked glucose residues, where the chains are in perfect alignment, the cellulose has a crystalline structure. The cellulose fibrils are generally embedded in other polysaccharide material, e.g. the hemicelluloses in the higher plants. 3 [FROM INTRODUCTION]Item A study of the acceptability of Holcus spp. to Perendale sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Plant Science at Massey University(Massey University, 1979) Cameron, Nicholas EvanVarious characters are reputed to reduce the acceptability of Yorkshire fog grass (Holcus lanatus) to sheep. The relative importance of these characters in determining the acceptability of Yorkshire fog to sheep was investigated in summer, autumn, and early-winter of 1978, using standardised regression, and based upon a phenotypically diverse collection of spaced plants from fifty-three seed populations. A clump defoliation score was used to assess sheep preference. Cluster analysis of ratios of the standardised partial regression coefficients from individual genotype populations generally confirmed the results obtained from the standardised partial regression coefficient ratios of pooled genotype populations. Sheep rejected plants exhibiting a high proportion of inflorescences, dead leaf and sheath material and crown rust infection. The presence of inflorescences and crown rust were respectively 1.5 and 0.86 times as important as clump greenness over all genotype populations, in the summer period. Leaf pubescence was only 0.13 times as important as clump greenness and was therefore considered relatively unimportant in determining sheep preference. Leaf tensile strength, leaf width, clump height and diameter, clump erectness, leaf flavanol level and soluble sugar level, were also considered unimportant in this study, and ranged from 0.57 to 0.019 times as important as clump greenness in determining sheep preference. However only 20-25% of the variation in sheep preference was explained by the characters examined in the three seasons of this study. The unexplained variation may have been due to a high level of amongst sheep preference variance or to unassessed plant characters. The phenotypic variation of each character was partitioned using a split-plot-in-time model. Broad-sense heritability estimates for all characters examined were low and ranged from 34% to 0.4%. It was suggested from these results that the acceptability of Yorkshire fog grass to sheep, by reduction of inflorescences and crown rust infection, and by removal of excessive dead leaf and sheath material, was largely under the control of grazing management (i.e. an aspect of the environment). However, some progress might be achieved by selection and breeding for genotypes with reduced levels of inflorescences (h2= 34%) and crown rust infection (h2= 29%).Item Intraspecific variation in Yorkshire fog within a limited geographical region : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Botany at Massey University(Massey University, 1973) Burgess, Robert EdwardTopodemes of Yorkshire fog were sampled from within a 50 km radius of Massey University, from ecologically diverse sites, and grown under uniform environmental conditions in order to study the variation in various plant characters between them. In the first of the two experiments undertaken, topodemes were compared as spaced plants in an experimental field. Several characters related to the sexual phase of the life cycle of this perennial grass species (panicle production, seed weight and survival-vigour of plants subsequent to flowering) were not observed to vary between topodemes. For the other such character measured (date of panicle emergence) the differences between topodemes observed were considered to reflect differences in time of pollen release. Thus, where source habitats of differentiated topodemes were in such close proximity that gene flow between them was likely, they were probably effectively isolated. In the second of the two experiments, topodemes were grown under three water treatments (waterlogged, plentifully watered and periodically dried) in 5-inch pots, one plant per pot, so that differences between topodemes and the effects of the different water treatments on the topodemes could be studied simultaneously. For different vegetative characters studied, topodemes were found to display stable and plastic response to the diverse water treatments, and to be differentiated both in mean response over all, and in pattern of response to, the water treatments. An attempt was made to determine the relationships between the responses of different characters, and between this hierarchy of plant response and environmental variability within and between source habitats. Differential topodeme responses could in some instances be considered to reflect adaptation to the source environmental conditions. Topodemes T10 and T02, from excessively drained sand dune habitats, possessed more densely hairy leaves, and produced longer laminae under the dry treatment, than topodemes from wetter source habitats. T10 under the dry treatment was able to withstand a greater degree of internal moisture stress than other topodemes before showing signs of wilting. T02 under the dry treatment possessed fewer stomata than topodemes T01 and L02 from marsh and swamp habitats respectively, and in mean response over all water treatments possessed broader laminae than topodemes P02, P04 and L00, also from habitats in which water table level was high throughout the year. P04 and L02 from continuously waterlogged source habitats produced longer laminae under waterlogging than other topodemes, and the latter topodeme, again under waterlogging, possessed a significantly greater mean compressed diameter than other topodemes. However, the evidence for this adaptation did not involve direct experimentation, and therefore the possibility that the genetic divergence demonstrated between topodemes was due to various chance effects, rather than disruptive selection, was not considered irrelevant.Item The complexing of calcium and magnesium by organic plant constituents : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy, Chemistry/Biochemistry Department, Massey University(Massey University, 1971) Molloy, Leslie FrancisThe definition, occurrence and aetiology of hypomagnesaemic tetany is discussed as an introduction to the practical implications of the present investigation. The current hypotheses, involving an unfavourable pasture chemical composition, accounting for the binding of Ca++ and Mg++ in the intestinal tract of ruminants are reviewed. The role of undigested or partly-digested plant cell wall materials is advanced as another such hypothesis, and the present investigation of the cell wall polymers of a typical pasture grass is outlined. The comprehensive analysis of the grass Yorkshire fog (Holcus lanatus) involves, initially, the extraction and purification of pectic substances, lignin, hemicelluloses and cellulose. The non-volatile organic acid content of the grass is also determined. Analytical methods are developed and evaluated in order to assess the homogeneity of these isolated cell wall fractions, and their chemical constitution investigated to aid in determining any possible relationship between cation complexing and polymer (or monomer) structure. The pectic fraction isolated from Yorkshire fog is approximately 90% polygalacturonic acid while the hemicelluloses are basically arabinoxylans with varying hexose and uronic acid content. Attempts tofractionate the predominant hemicellulose, hemicellulose B, into homogenous arabinoxylans gives inconclusive results. Most of the chemical evidence, however, indicates the presence of three discreet polysaccharides in this fraction - a simple arabinoxylan, an acidic galactoarabinoxylan and a neutral glucan. Infrared and ultraviolet spectroscopy is utilised to determine the purity of the isolated lignin as well as the presence of typical lignin functional groups. Yorkshire fog lignin has a moderate phenolic hydroxyl and -OMe content and, like most other monocotyledonous lignins, gives yields of syringaldehyde, vanillin and p-hydroxybenzaldehyde on alkaline nitrobenzene oxidation. The outstanding feature of the lignin is its appreciable content of etherified hydroxyl groups in the 4-position of the aromatic ring and the low yield of syringaldehyde. The water-soluble, non-volatile organic acids are quantitatively determined by anion-exchange resin chromatography and their identity confirmed by paper chromatography. The major acid is the tricarboxylic acid, trans-aconitic acid, which is determined spectrophotometrically. The normal plant acids, citric and malic, are present in moderate quantities while the alicyclic acids, quinic anc shikimic, are only present in minor amounts. A limited amount of data on the seasonal fluctuation of these organic fractions in Yorkshire fog is presented. Electrolytes and the concept of ionic activity are discussed in the introduction to the study of the ability of these plant fractions to bind Ca++ and Mg++ in an aqueous salt solution of cationic composition similar to that of the intestine of a ruminant. A cation exchange method is developed whereby changes in the activity of Ca++ or Mg++ on the introduction of a plant fraction into the salt solution are reflected in the cationic composition of the equilibrium resin. An investigation is undertaken of a large number of calibration solutions varying in [ca++] and[Mg++], but constant in [Na+], [K+] and [NH4+], the latter cations being present in excess as 'swamping' cations. Regression expressions relating solution cation concentration to the equilibrium resin cation concentrations are derived and used as calibration equations to determine the amounts of bound and ionic Ca++ and Mg++ in solutions in equilibrium with the plant fractions. The pectic substances, lignin and the organic acids are effective in complexing a large proportion of the solution Ca in a non-ionic form but only lignin and the organic acids display a significant complexing of solution Mg++. Except for hemicellulose B (branched) at a slightly alkaline pH, the hemicelluloses and cellulose have little ability to complex either Ca++ or Mg++. The complexing results are discussed in terms of the relationship of polymer structure to observed cation affinity. Factors involved in cation binding are: - the charge and degree of hydration of the cation itself; - distribution and degree of esterification of carboxyl groups in the polymer; - monomer conformation; - type of glycosidic linkage in the polymer; - the possibility of hydrogen-bonding and non-bonded interactions between substituents on the polymers; - solution pH. The in vivo implications of the results are finally discussed in the context of general ruminant nutrition and alkaline-earth metal absorption discussed in the introduction.Item Comparative studies on the implications of condensed tannins in the evaluation of Holcus lanatus and Lolium spp. swards for sheep performance : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand(Massey University, 1995) Montossi, FabioThe series of experiments which form the basis of the present study concentrated on evaluations of: (i) diet selection, grazing behaviour, herbage intake, and sheep performance between Holcus lanatus (Yorkshire fog) and Lolium spp. (perennial or annual ryegrass) swards both associated with Trifolium repens (White clover), and in one study with the presence or absence of Lotus corniculatus (Birdsfoot trefoil), and (ii) the effects of condensed tannins (CT) on the behaviour and performance of sheep grazing those swards. The effects of CT on sheep production were assessed by twice daily oral administration of polyethylene glycol (PEG; Molecular weight 4,000) to half of the lambs on each sward combination. Three grazing experiments are reported; the first two (Experiments 1 and 2) were carried out at Massey University (New Zealand) from 1992 to 1993, while the final trial was undertaken at INIA Tacuarembó Research Station (Uruguay) during 1994. In the first experiment (Chapter 3), relationships amongst sward, grazing behaviour, and animal performance variables were studied on perennial ryegrass/white clover and Yorkshire fog/white clover swards rotationally grazed by ewes at medium and high daily allowances (6% and 12% of liveweight as herbage dry matter respectively) during late autumn in 1992. The next experiment (Chapter 4) was designed to investigate the effects of low concentrations of condensed tannins (CT) on lambs grazing perennial ryegrass/white clover or Yorkshire fog/white clover swards at a constant height of approximately 6 cm from December 1992 to March 1993. The final experiment (Chapter 5) was carried out from August to early November 1994 to examine differences in behaviour and performance between annual ryegrass/white clover and Yorkshire fog/white clover swards, both with presence or absence of birdsfoot trefoil, rotationally grazed by lambs Results from Experiments 1 and 2 showed that herbage intake achieved by sheep grazing perennial ryegrass swards was 15 - 27% higher than that achieved on Holcus lanatus swards. Bite weight was 13 - 38% greater for Holcus lanatus than for ryegrass, associated with the 15 - 25% greater sward bulk density. There was a consistent advantage (1 - 5%) in the organic matter digestibility of the herbage selected in favour of ryegrass swards. Sheep on both pasture types concentrated grass rather than clover in the diet. Sheep grazing on ryegrass swards had higher liveweight gains (8 - 51%), clean wool growth (6%), carcass weight (7%), GR values (22%), and carcass dressing out percentage (2%) than sheep grazing on Yorkshire fog swards. The stocking rate maintained on ryegrass plots was 25% greater than that on Yorkshire fog plots. Similar low concentrations of CT were recorded in the diets of ryegrass and Yorkshire fog swards (≤ 0.2% on a DM basis). These results were confirmed by measurements of NH3 concentration in the rumen fluid. The low levels of CT had no significant effects on diet selection, herbage intake, grazing behaviour patterns or lamb performance. However, the lambs grazing on Yorkshire fog swards showed small and non-persistent responses to CT in terms of faecal egg counts, wool growth and liveweight gain. Experiment 3 indicated that the organic matter digestibility of the diet selected and the herbage intake of lambs grazing on Yorkshire fog swards were higher than those on annual ryegrass (5% and 24% respectively), reflecting the higher contents in the diet of grass green leaf and of legume and the lower content of dead material in favour of Yorkshire fog swards. Lambs grazing on both swards showed similar behaviour patterns. Those on Yorkshire fog swards had higher clean wool growth (15%). greater fibre diameter (48%), and longer fibre length (5%), greater liveweight gains (41%), final weight (11%), carcass weight (29%), carcass weight gains (29%), GR value (38%), and lower faecal egg count (FEC) values (20%). Slightly higher CT dietary concentrations were recorded in Yorkshire fog swards than in annual ryegrass (0.420 vs 0.365 ± 0.02% on a DM basis). These low CT levels increased clean wool growth (11%), fibre diameter (4%), although differences in carcass measurements were relatively small, and tended to reduce FEC values (15%). The effects of CT on animal performance were greater in Yorkshire fog swards than in perennial ryegrass swards. CT had no significant effects on diet selection, herbage intake, or grazing behaviour patterns. The very small effects of lotus on sward composition, sward structure and on lamb performance were explained by its very low contribution to both swards. The major conclusions of the first two experiments are as follows: (i) under high fertility conditions and intensive grazing management, perennial ryegrass/white clover swards appeared to have higher feeding value than Yorkshire fog/white clover swards for sheep production; (ii) the results of these experiments confirmed the presence of limited CT concentrations in Holcus lanatus, and provided further evidence that low CT concentrations also exist in perennial ryegrass; (iii) these low CT concentrations (≤ 0.2% on a DM basis) present in both swards did not influence sheep performance significantly. Finally, the conclusions of the last experiment were: (i) under low to moderate soil fertility conditions and lax rotational grazing management, Yorkshire fog swards had better composition and structure for lamb production than annual ryegrass, as a consequence of the early reproductive development in annual ryegrass; (ii) low CT concentrations (range 0.36 to 0.42% on a DM basis) consistently increased wool production and liveweight gains, particularly in Yorkshire fog swards. The findings of these studies are discussed (Chapter 6) in the context of the role of Holcus lanatus for grazing systems and of the potential benefits of low dietary CT concentrations in Holcus lanatus and Lolium spp. for animal production. Keywords: Lolium perenne (perennial ryegrass); Lolium multiflorum (annual ryegrass); Holcus lanatus (Yorkshire fog); Trifolium repens (White clover); Lotus comiculatus (Birdsfoot trefoil); Polyethylene glycol (PEG); Condensed tannins (CT); herbage intake; diet selection; grazing behaviour and lamb production.Item Comparative evaluation of diet selection, herbage intake and performance of lambs grazing Yorkshire fog (Holcus lanatus L.), perennial ryegrass (Lolium perenne L.), and tall fescue (Festuca arundinacea Schreb.) and assessment of effects of condensed tannins (CT) in the grasses on lamb performance : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Plant Science Department of Massey University, Palmerston North, New Zealand(Massey University, 1996) Liu, FuyuanA series of grazing experiments was carried out at the Pasture and Crop Research Unit, Massey University, Palmerston North, New Zealand, to compare Yorkshire fog (Holcus lanatus cv. Massey Basyn)/white clover (Trifolium repens cv. Grasslands Tahora) with perennial ryegrass (Lolium perenne cv. Grasslands Nui)/white clover cv. Grasslands Tahora and tall fescue (Festuca arundinacea cv. Grassland Roa)/white clover cv. Grasslands Tahora pastures with reference to grazing behaviour, diet selection, herbage intake and performance of lambs, and to specifically assess the effects of low concentrations of condensed tannins (CT) in grasses on body growth and wool growth of animals. Half of the lambs were drenched with polyethylene glycol (PEG) (CT inactivated) and the remainder were drenched with water as a control (CT acting) in each experiment. PEG is assumed to specifically bind and inactivate CT without influencing the digestion of other nutrients. In the first experiment, a comparative study of grazing behaviour, diet selection, herbage intake and performance of lambs grazing Yorkshire fog/white clover and ryegrass/white clover swards was made from late May to late June, 1993. Thirty-six lambs, balanced in sets of six based on initial fasted weight continuously grazed paddocks with three replicates of the two pasture treatments for 7 weeks. Yorkshire fog had greater sward bulk density and intake per bite (68 vs 51 ± 7.1 mg OM/bite) than ryegrass. Perennial ryegrass had a consistent superiority over Yorkshire fog in organic matter digestibility (OMD) (80 vs 77 ± 0.3 %, P≤0.05) and herbage OM intake (1117 vs 930 ± 31.5 g/day, P≤0.1), resulting in faster liveweight gain (174 vs 144 ± 9.7 g/day), significantly higher carcass weight (17.7 vs 16.3 ± 0.1 kg, P≤0.05) and dressing out % (49 vs 48 ± 0.2, P≤0.05). Low CT concentrations (1.7 - 2.2 g/kg DM) were found in the diets selected from both the grasses; these low CT concentrations had no effect on grazing behaviour, diet selection and herbage intake. Small responses to PEG administration were observed in initial liveweight gain, but PEG had no effects on overall liveweight gain, carcass weight, carcass weight gain and GR (depth of total soft tissue over the 12th rib at a point 11 cm from the mid carcass). The next two experiments were designed to compare Yorkshire fog cv. Massey Basyn)/white clover cv. Grassland Tahora with tall fescue cv. Grassland Roa/white clover cv. Grassland Tahora pastures in terms of grazing behaviour, diet selection, herbage intake and performance of lambs, and to further quantify the effects of low CT concentrations in the grasses on lamb performance, especially on initial liveweight gain of lambs, under rotational grazing management in late spring, summer and early autumn, 1993/1994. The comparisons between Yorkshire fog and tall fescue pastures were made under similar sward conditions. Previous grazing experience on the appropriate pasture and sex were designed as treatments as well as pasture species and PEG supplementation. Forty-eight lambs balanced for previous grazing experience and sex in sets of sixteen were used in each experiment. One group of 16 was slaughtered as the initial group at the start of each experiment to measure the carcass weight. The other two groups of lambs grazed six paddocks of each pasture treatment in a 30-day rotation. Tall fescue had higher total N than Yorkshire fog in early December (3.56 vs 3.43±0.018 % DM, P≤0.05) and late February (3.24 vs 2.91 ±0.022 % DM, P≤0.0001), and had higher OMD in early December (81 vs 78 ±0.6 %, P≤0.01) and late February (72 vs 68 ± 1.1 %, P≤0.05), but lower OMD in early February (71 vs 74 ± 1.1 %, P≤0.05). Yorkshire fog produced faster liveweight gain (99 vs 76 ± 6.7 g/day, P≤0.1), greater carcass weight (14.7 vs 13.9 ± 0.2 kg, ≤0.05) and faster carcass weight gain (32 vs 20 ± 3.1 g/day, P≤0.05) than tall fescue in late spring and summer (Experiment 2), but not in late summer and early autumn (Experiment 3). Male lambs had faster liveweight gain than female lambs in Experiment 2 (95 vs 80 ± 3.3 g/day, P≤0.05) and in Experiment 3 (80 vs 72 ± 2.3 g/day, P≤0.05). Previous grazing experience had no effects on final liveweight gain, carcass weight, carcass weight gain. There was no significant effect of interaction between previous pasture and current pasture on these parameters. The results of the experiments further confirmed the low CT concentrations (1. - 2.1 g/kg DM) present in Yorkshire fog in Experiment 1 and small responses of lambs to PEG supplementation in initial liveweight gain only in Yorkshire fog (101 vs 92 ± 4.1 g/day, P≤0.1) in Experiment 2. There were no significant effects on carcass weight, dressing out, GR and wool growth rate. Lower faecal egg counts in lambs in Yorkshire fog than in tall fescue suggested some potential of Yorkshire fog for parasite control. The low CT concentrations in the Yorkshire fog reduced to some extent rumen ammonia concentration, but were not enough to effectively promote animal performance. The relatively low CT concentrations detected in tall fescue were probably an artifact, because there was no PEG effect on rumen ammonia concentration for tall fescue. The final grazing experiment was conducted to evaluate grazing behaviour, herbage intake and performance of lambs as affected by grazing selection opportunity and low condensed tannin (CT) concentrations in Yorkshire fog/white clover pasture under rotational grazing management from late November, 1994 to early February, 1995. Twelve lambs were slaughtered as the initial group at the start of the experiment to measure the preliminary carcass weight. Forty-eight lambs were allocated to two groups in sets of twenty-four and rotationally grazed eight paddocks each of 0.1 ha, in which a "leader" group of 24 lambs grazed each paddock for four days, followed by a similar "follower" group of 24 lambs grazing for four days. The leader/follower grazing regime created the desired contrasts in herbage quality and quantity. The superiority in sward allowance, selection opportunity, diet quality and reduced possibility of infection by worm parasites resulted, as expected, in faster body growth and wool growth rate in the 'leader' lambs than in the 'follower' lambs. The results of the experiment further confirmed the findings of the influence of low CT concentrations in Yorkshire fog on rumen ammonia concentration. The effect of low CT concentrations on animal performance was not different for generous and restricted grazing. The following general conclusions can be drawn from this series of experiments: 1) The diets selected by sheep comprised more green material and less dead material than the swards offered to the animals, while diet composition was determined largely by the structure and distribution of sward components rather than by deliberate selection by the animals. 2) Herbage OM intake was influenced to a greater extent by nutritional factors than by behavioral limitations, there being substantially higher herbage OMD and OM intake on ryegrass than on Yorkshire fog in winter. 3) Perennial ryegrass/white clover pasture tended to have higher animal production than Yorkshire fog/white clover pasture under continuous grazing management in winter, and Yorkshire fog pasture produced slightly higher animal performance than tall fescue in rotational grazing management in late spring and early summer. 4) The results of the trials confirmed that low CT concentrations (0.18 - 0.32 % on a DM basis) were present in Yorkshire fog, and provided evidence that perennial ryegrass contained relatively low CT concentrations, but the low CT concentrations detected in tall fescue were probably an artifact of the current procedures of analysing CT. 5) The low CT concentrations in the grasses had no effect on grazing behaviour, diet selection or herbage intake. The low CT concentrations in Yorkshire fog to some extent reduced rumen ammonia concentration, but were not enough to effectively improve animal production.