School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemSome effects of botanical composition of pasture on the liveweight and wool production of sheep( 1972)Until recently, the main evidence on which to base pasture mixture. recommendations in Victoria, has been district experience and the results from dry matter ( "mowing") experiments. The grazing experiments described in this thesis, were initiated by Messrs. R. Twentyman, R. Newman, R. Allen and K. Maher of the Department of Agriculture during the period, 1960-196. Their aim was to develop some objective appreciation of the relative value for animal production of some of the sown and unsown species in Western district pastures. In addition to pasture species evaluation, they sought information on the relationship between pasture growth and animal production. Such information is needed so that Agrostologists can better evaluate the many pasture management factors (such as fertilizers, seeding rates, seed. treatments, herbicides, insecticides and defoliation treatments) that affect pasture growth and for which advice is frequently sought.
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ItemAttributes of pasture influencing the diet of grazing sheep( 2002)This thesis investigated how the composition, productivity and nutritive quality of Phalaris aquatica L. (phalaris) and Trifoliun: subterranean L. (subterranean clover) pasture affected diet selection and intake by sheep in temperate Australia. Field experiments were conducted at the Ginninderra Experiment Station, Canberra, (35 17' S, 149 08' E) and glasshouse experiments at the CSIRO Division of Plant Industry, Black Mountain Laboratories, Canberra, Australia. The effects of different defoliation treatments on the ability of grass and subterranean clover to compete for light were studied in a glasshouse experiment. Regular patterns of phalaris and subterranean clover were planted on a 25 mm grid to create swards with 0% clover, 25% clover, 50% clover, 75% clover and 100% clover by plant number. Swards were either defoliated regularly by clipping to 2, 4, 9 or 15 cm tall or not defoliated and harvested when they reached 2, 4, 9 or 15 cm tall. The distribution of leaf area index within the swards was measured and related to light interception and photosynthesis. Light infiltrated further into the canopy of unclipped swards than clipped swards. Regular clipping created a dense layer of planophile leaves at the top of the canopy, which intercepted most of the incident light, leaving the lower canopy in darkness. Consequently, the lower canopy contributed less to photosynthesis in clipped swards than in unclipped ones. Grass leaves were displayed more prostrate when clipped regularly such that the structure and light interception of grass was similar to clover. In the absence of defoliation, grass leaves were taller than clover, but their erect habit allowed infiltration of light to clover laminae. The relationships between herbage mass, botanical composition, intake and dietary selection by sheep grazing phalaris-subterranean clover pastures were investigated during spring. A range in pasture height (1.2 to 10.2 cm) caused a similar range in herbage mass (370 to 3030 kg DM/ha) and herbage accumulation (-18 to 52 kg/ha/day). A pasture 5 to 6 cm tall, with a leaf area index of 2.0 and an available yield of 1700 kg DM/ha was most productive. The estimated daily pasture intake by sheep ranged from 384 to 1077 g OM. On the shortest pastures, intake was limited by available yield. Intakes increased little after available pasture yield reached 1500kg DM/ha or a pasture height of 5 to 6 cm, but were restricted at pasture heights of 2-3cm or less. There was no evidence for selection in favour of either clover or phalaris, and they were consumed in the same proportion they were present in the pasture. The effect of recent diet on the selection and intake of diet by sheep grazing phalarisclover pastures was investigated. Sheep grazed phalaris, clover or phalaris-clover pasture prior to movement to either a phalaris- or clover-dominant mixture of the two species. The results were complicated by the presence of Vulpia species in the pastures. Where one species dominated the pasture, the diet was predominantly that species. Cases where pasture was a more even mixture of species could not be interpreted successfully, because the alkane concentrations of the pasture species (from which diet composition estimates were made) did not allow the pasture species in the diet to be discriminated with confidence. The daily intake of pasture was affected by previous diet, with animals tending to consume more when moved to a pasture similar to the one they were previously grazing. In an experiment on established phalaris pasture, the diurnal fluctuation in the concentration of water-soluble carbohydrates (WSC) was measured during spring. WSC increased significantly (P = 0.009) from 103 mg/g DM at 0715 hours to 160 mg/g DM at 1300 hours, and did not change further during the next two hours. The concentrations of glucose (17 mg/g DM), fructose (20 mg/g DM), fructan (14 mg/g DM) and "other carbohydrate" (predominantly the carbohydrate moiety of glycosides; 43 mg/g DM) remained relatively constant throughout the daylight period. The increase in concentration of sucrose (33 mg/g DM) was the most significant influence on the increase in WSC (57 mg/g DM). Shading to exclude light prevented the increase in WSC concentration during the day. In a subsequent experiment, a shading treatment was used to create pasture with lower WSC concentration (62 mg/g DM) than an unshaded control (126 mg/g DM). The concentration of the component carbohydrates (i.e. glucose, fructose, sucrose, fructan, "other carbohydrate" and starch) were significantly lower in shaded compared to unshaded pasture. Sheep given free choice between shaded and unshaded pasture exhibited a preference for unshaded pasture over shaded pasture and, on average, 72% of the DM in their diet was unshaded pasture. Whilst no sheep showed preference for the shaded pasture, the proportion of unshaded pasture in their diets varied between 52% and 87% (DM basis). The results are discussed in terms of their implications for grazing management and the development of strategies to improve pasture utilisation and nutritive quality. The role of WSC in diet selection and its importance as a determinant of forage nutritive quality are discussed. The potential benefits of increasing the concentration of WSC in forages by altering agronomic practices or selectively breeding for WSC are discussed.
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