No description available.

The grazing behaviour and diet selection of a vertebrate herbivore, the domestic sheep (ovis aries L.), feeding in patchy perennial ryegrass (Lolium perenne L.) monocultures was investigated. Heterogeneity or patchiness was created by manipulating (1) the nutritional content of ryegrass, (2) parameters of sward structure e.g. sward height, pseudostem and lamina length, and tiller density, and (3) brightness of ryegrass relative to the background sward. Patches were either fertilised turves transplanted into paddock swards or were created in situ by local fertilisation, trimming etc. The background sward was low in nitrogen (<1.0%N dry weight) compared with average ryegrass leys found on farms in British lowland areas. Sheep preferred to graze in transplanted patches of ryegrass. These patches were structurally similar to the background sward, but were higher in nitrogen content and digestibility as a result of fertilisation. Thus, sheep actively selected more nutritious ryegrass. There was a significant quantitative relationship between brightness and the nitrogen and water soluble carbohydrate content of ryegrass. Darker green ryegrass had a higher nitrogen content and lower water soluble carbohydrate content than lighter green ryegrass. It is suggested that sheep learned to use brightness as a cue in intra-specific forage selection. They had a high preference for short, dark green patches of similar height to the lighter green, background sward. Sheep also preferred to graze in tall patches of ryegrass (>10 cm taller than the background sward) regardless of their nutritional content or brightness relative to the background sward. It is likely that sheep use a multiplicity of physical cues associated with perennial ryegrass in diet selection. The interaction between structural and sward parameters and nutrition content of forage in influencing diet selection requires further investigation. In further experiments, an optimal foraging model, the marginal value theorem was used to make predictions about the behaviour of sheep grazing in monocultures containing highly preferred transplanted patches of tall, fertilised ryegrass. By manipulating the cost of travel between these good ryegrass patches and by detailed measurements of intake within patches by individual sheep, I was able to make quantitative predictions about the time spent grazing in each patch. Travel time and costs were increased by moving good patches further apart and by hobbling sheep to slow down their speed of movement. As predicted by the marginal value theorem, average time spent in a patch was positively correlated with average travel time between patches. For two sheep, the predicted and observed times spent in patches were statistically similar at low travel times, while at higher travel times, observed times were greater than predicted. For a third sheep, all observed times were greater than predicted. Thus overall, there was not a good quantitative fit between the model and the observed behaviour. While incorporation of the difference in the energetic cost of travel relative to that of grazing in a good patch into the model resulted in an increase in predicted optimal patch residence times, the fit between predicted and observed values was not significantly improved. Reasons for this difference between observed and predicted patch residence times are discussed. However, these experiments demonstrated that patch-use foraging models may be more useful than prey models in investigating grazing behaviour of vertebrate herbivores, and that travel time between patches of forage is a previously unidentified constraint of sheep grazing behaviour.

No description available.

Renal blood flow and micropuncture studies were conducted in late gestation fetal sheep (gestational age 134 - 141 days; term 150 days) and neonatal lambs (8 - 18 days after birth) to study the forces involved in glomerular filtration (GFR) and characterize the tubuloglomerular feedback (TGF) system during development. These studies required the kidney to be immobilized so stable models in acutely prepared anaesthetized animals were developed. Fetuses were studied in a heated water bath exteriorized from the uterus but with an intact umbilical circulation. The lower GFR in fetuses than lambs was found to be due to both lower net filtration pressures (P<0.001) and a lower ultrafiltration coefficient (P<0.001). TGF was present at both ages, but in fetuses the sensitivity was higher (P<0.001) and reactivity was lower (P<0.001). The reduction in TGF sensitivity between fetal and neonatal life may facilitate the increase in renal blood flow and GFR which occurs at this time. In both fetuses and lambs the sensitivity of the TGF curve was reduced by volume expansion (P<0.001, P<0.05) and reactivity was reduced in lambs (P<0.001). Furosemide abolished TGF at both ages. In both fetuses and lambs, TGF reactivity was increased by inhibition of neuronal nitric oxide synthase (nNOS; P<0.01, P<0.001) and in lambs, TGF sensitivity was increased (P<0.01). This indicates that nitric oxide produced by the macula densa modulates TGF during development. In offspring destined to become hypertensive due to maternal dexamethasone treatment in early gestation TGF sensitivity tended to be enhanced in fetal life and was enhanced in lambs (P<0.01). Increased TGF sensitivity may contribute to the development of hypertension in this model of developmental programming. The effects of nNOS inhibition were attenuated in these animals, suggesting that they have low tonic production of nitric oxide by the macula densa. In fetuses whose mothers had been subtotally nephrectomized prior to mating to induce maternal mild renal impairment, GFR was increased (P<0.01) but net filtration pressure was reduced (P<0.001) so the ultrafiltration coefficient was increased (P<0.001). TGF sensitivity was normal and the effects of nNOS inhibition were similar to normal fetuses.

The objective of this thesis was to better understand the epidemiology of caseous lymphadenitis (CLA) and its economic effects on the Australian sheep industries. The work also sought to apply this knowledge to better understand how to control the disease in Australian sheep flocks. The occurrence of CLA in some other species, as a comparison to CLA in sheep, is described in the literature review. However a comprehensive review of research on CLA in all livestock species is not needed to meet the aims of the thesis. The research used serological tests developed in the 1970s and ‘80s to examine the epidemiology and costs of CLA in Western Australian sheep flocks. Epidemiological techniques were used to determine the main risk factors associated with high incidences of CLA. Controlled experimentation was used to better understand the spread of CLA within flocks. Prevalence data collected at abattoirs and survey techniques were employed to better understand how CLA was being controlled in Australian sheep flocks. It was shown that toxin and cell wall ELISA tests for CLA were useful tools to study the spread of CLA in sheep flocks. Using the serological tests it was estimated that 80 per cent of CLA spread occurs after the second and third shearings. This knowledge was used to design a risk factor study which identified two significant factors associated with high CLA spread, that is in dips and close contact after shearing. These tests also facilitated the study of new CLA infection on wool production. It was found that sheep produce approximately five per cent less clean wool in the year in which they are infected. The main routes for the spread of CLA were from sheep with lung abscesses to those with skin cuts and through dips, rather than from an environment contaminated with Corynebacterium pseudotuberculosis bacteria. A survey of sheep producers found that the prevalence of CLA had decreased from over 50% in the 1970s to approximately 20% in the late 1990s. It also found that current vaccines were being used inefficiently. Large increases in the efficiency of control can be achieved by approximately 70 per cent of producers by using commercially available vaccines and the recommended vaccination programs of two

Includes bibliographical references (leaves 197-259). / xv, 261, [9] leaves, [17] leaves of plates : ill. (some col.) ; 30 cm. + 1 videocassette (6 min. (VHS) : sd., col. ; 1/2 in.) / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Consists of a review of rumen ciliates, their implications in ruminant nutrition and a description of the research methods, the results and the conclusions drawn with regard to the prospects of establishing an immunological basis for the manipulation of rumen ciliates. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1994

Thesis (Ph. D.)--University of Adelaide, Dept. of Animal Sciences, 1986. / Includes bibliographical references (leaves 191-207).

Thesis (Ph. D.)--University of Wyoming, 2005. / Title from PDF title page (viewed on Nov. 14, 2007). Includes bibliographical references (p. 167-211).

Thesis (M. Ec.)--University of Adelaide, Dept. of Economics, 1992. / Errata inserted. Includes bibliographical references (leaves 64-66).

Thesis (M.Ag.Sc.)--University of Adelaide, Dept. of Animal Physiology, 1977.