Includes bibliographical references (leaves [259]-290) Investigates nitrogen assimilation and metabolism in rumen bacteria with the object of understanding the basic process and their controls.

Includes bibliographical references (leaves 122-138). / xvii, 138 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates the use of microbial inoculants to prevent the onset of acidosis in acutely grain fed animals; and, the most effective combination of virginiamycin and lactic acid utilising bacteria (selenomonas ruminantium subsp. lactilytica and Megasphaera elsdenii) in controlling lactic acid accumulations in vitro. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Science, 1995

Includes bibliographical references (leaves [259]-290) / xxviii, 290 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates nitrogen assimilation and metabolism in rumen bacteria with the object of understanding the basic process and their controls. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1991

Bibliography: leaves 122-138. Investigates the use of microbial inoculants to prevent the onset of acidosis in acutely grain fed animals; and, the most effective combination of virginiamycin and lactic acid utilising bacteria (selenomonas ruminantium subsp. lactilytica and Megasphaera elsdenii) in controlling lactic acid accumulations in vitro.

This study was conducted in two trials. The aim was firstly to identify the qualitative characteristics of Atriplex nummularia (Hatfield Select). Goats and sheep were used to identify three palatability groups of plants in the A. nummularia (Hatfield Select) paddock. These palatability groups were compared in terms of quality to one another. Secondly, qualitative and quantitative intakes of A. nummularia (Hatfield Select) by goats and sheep were determined. This was done in a grazing trial lasting five days. A comparison was conducted between goats and sheep as well as between the different days of the grazing period. During the first trial, goats and sheep were used to identify the most-, medium- and least-palatable A. nummularia (Hatfield Select) plants. The regrowth on these plants were harvested and used for laboratory analysis to identify the qualitative differences between these three groups. These samples were also used to determine and compare degradability between the three groups as well as between goats and sheep. Goats and sheep preferred A. nummularia (Hatfield Select) plants with a significantly (p ¡Ü 0.05) higher crude protein (CP), phosphorus (P) and magnesium (Mg) content. The most preferred plants also had higher neutral detergent fibre (NDF), Ca, K, Na, Cl- and Cu content than the least preferred plants, but these were not significant (p > 0.05). A. nummularia (Hatfield Select) provides enough CP for maintenance and production in both goats and sheep. All mineral requirements for maintenance in goats and sheep can be satisfied on A. nummularia (Hatfield Select), except that of Cu. For production (growth and lactation) only P is deficient and needs to be supplemented. A. nummularia (Hatfield Select) makes an ideal drought fodder crop to support the natural veld during the dry season. An overall higher DM, N and NDF rumen degradability of Atriplex was recorded with goats than with sheep. Goats exhibited a significantly (p ¡Ü 0.05) higher DM and N degradation and although a higher NDF degradation was also recorded, this was not significant. The rate of DM, N and NDF rumen degradation was also higher in goats than in sheep. This means that goats have a more favorable rumen environment for the digestion of A. nummularia (Hatfield Select). DM and N degradation were also significantly (p ¡Ü 0.05) higher in the most palatable group than the least palatable group. NDF degradability decreased with palatability. This means that the most palatable plants have a higher digestibility and quality than the least palatable plants. In the second experiment, rumen and oesophageal fistulated sheep and goats were allowed to graze A. nummularia (Hatfield Select) for five days. Qualitative and quantitative intakes were determined. The quality and quantity of ingested material were compared between goats and sheep as well as between the different grazing days. There was a significant decline in the quality and quantity of intake over the grazing period. Some parameters were significant, for example CP. The CP concentration declined from 18% to 3.91 % for goats and from 19.88% to 6.61% for sheep. The cell wall constituents (NDF) increased by about 10% from the start to the end of the grazing period. IVDOM decreased by 14% and intakes were almost halved from the start to the end of the grazing period. Other authors have also observed this decrease in quality and quantity of intake over time. The lower quality and quantity in intake was because of a decline in the availability of high quality edible material. At the end of the grazing period, there was very little edible material left which caused an extremely low quality and quantity of intake. Rumen NH3-N concentrations also declined as the dietary CP declined, but it was still present in high enough concentrations to sustain the rumen micro flora population. Rumen VFA decreased over the grazing period. The acetic acid to propionic acid ratio increased towards the end of the grazing period. This caused a decline in the efficiency of utilization of ME for maintenance as acetic acid has an efficiency in utilization of ME of 59% and propionic acid of 86% (McDonald et al., 1995). This means that energy will have to be supplemented to sustain maintenance. / Dissertation (MSc (Agric) Animal Science, Nutrition)--University of Pretoria, 2007. / Animal and Wildlife Sciences / unrestricted

Ruminant livestock maintain an important role in meeting the nutrient requirements of the global population through their unique ability to convert plant fiber into human-edible meat and milk products. Volatile fatty acids (VFA) produced by rumen microbial fermentation of feed substrates represent around 70% of the ruminant animal's metabolic energy supply. Rumen fermentation profiles may directly impact productivity because the types of VFA produced are utilized at differing efficiencies by the animal. Improving our understanding of factors that control these fermentative outcomes would therefore aid in optimizing the productive efficiency of ruminant livestock. Improvements in animal efficiency are now more important than ever as the livestock industry must adapt to continue meeting the nutritional needs of a growing global population in the context of increased resource restrictions and requirements to lower the environmental impact of production. The relationship between diet and VFA ultimately supplied to the animal is complex and poorly understood due to the influence of numerous nutritional, biochemical, and microbial variables. The central aim of this body of work was therefore to explore and characterize how fermentation dynamics, rumen environmental characteristics, and the rumen microbiome behave in response to variations in the supply of fermentative substrate. The objective of our first experiment was to describe a novel in vitro laboratory technique to rank livestock feeds based on their starch degradability. This experiment also compared the starch degradation rates estimated by the in vitro method to the rates estimated by a traditional in situ method using sheep. A relationship between the degradation rates determined by these two procedures was observed, but only when feed nutrient content was accounted for. While this in vitro approach may not be able to reflect actual ruminal starch degradation rates, it holds potential as a useful laboratory technique for assessing relative differences in starch degradability between various feeds. Our second experiment aimed to measure changes in VFA dynamics, rumen environmental characteristics, and rumen epithelial gene expression levels in response to dietary sources of fiber and protein designed to differ in their rumen availabilities. Conducted in sheep, this study utilized beet pulp and timothy hay as the more and less available fiber source treatments, respectively, and soybean meal and heat-treated soybean meal as the more and less available protein source treatments, respectively. Results indicated that rumen environmental parameters and epithelial gene expression levels were not significantly altered by treatment. However, numerous shifts in response to both protein and fiber treatments were observed in fermentation dynamics, especially in interconversions of VFA. The objective of the third investigation was to assess whether the rumen microbiome can serve as an accurate predictor of beef and dairy cattle performance measurements and compare its predictive ability to that of diet explanatory variables. The available literature was assembled into a meta-analysis and models predicting dry matter intake, feed efficiency, average daily gain, and milk yield were derived using microbial and diet explanatory variables. Comparison of model quality revealed that the microbiome-based predictions may have comparable accuracy to diet-based predictions and that microbial variables may be used in combination with diet to improve predictions. In our fourth experiment, the objective was to investigate rumen microbial responses to the fiber and protein diet treatments detailed in Experiment 2. Responses of interest included relative abundances of bacterial populations at three taxonomic levels (phylum, family, and genus) in addition to estimations of community richness and diversity. Numerous population shifts were observed in response to fiber treatment. Prominent fibrolytic population abundances as well as richness and diversity estimations were found to be greater with timothy hay treatment and lower with beet pulp whereas pectin degraders increased in abundance on beet pulp. Microbial responses associated with protein treatment were not as numerous but appeared to reflect taxa with roles in protein metabolism. These four investigations revealed that significant changes can occur in VFA fermentation and rumen microbial populations when sources of nutrient substrates provided in a ruminant animal's diet are altered and that a new approach may be useful in investigating degradation of another important substrate for fermentation (starch) in a laboratory setting. Our findings also determined that animal performance can be predicted to a certain extent by rumen microbial characteristics. Collectively, these investigations offer an improved understanding of factors that influence the process of converting feed to energy sources in the ruminant animal. / Doctor of Philosophy / Ruminant animals, such as beef cattle, dairy cattle, and sheep, play a major role in delivering essential nutrients to the human population through their provision of meat and dairy products. The current growth projections of the global population, in addition to increased concerns surrounding greenhouse gas emissions and restrictions on resources such as land and water make it important for us to consider ways of optimizing the productivity of these animals. A unique feature of ruminants is their ability to conduct microbial fermentation of large amounts of plant matter in their rumens to produce energetically valuable compounds called volatile fatty acids (VFA), which are the primary source of energy that the animals use for growth, reproduction, and milk production. One promising way of improving animal productivity is to increase the amount of energy from the diet that becomes available to fuel the animal's body processes; however, the process of converting feed to VFA is complicated and currently not well understood. The overall aim of this body of work was therefore to explore various nutritional, ruminal, and microbial factors that are known to impact fermentation in order to 1) increase our understanding of how these factors interconnect and 2) put us in a better position to manipulate these factors for optimal animal performance. The goal of our first experiment was to devise and use a novel laboratory technique to rank livestock feeds based on the degradability of their starch content, which is an important substrate for VFA fermentation. Our observations indicate that this technique may be a useful tool to help us determine relative differences between feeds based on their starch degradabilities in a laboratory setting. Our second experiment investigated the effects of feeding varying sources of fiber (beet pulp and timothy hay) and protein (heat-treated and untreated soybean meals) to sheep in terms of their VFA fermentation, rumen conditions, and the expression of certain key genes in the epithelial tissue of the rumen wall. While rumen environmental characteristics and epithelial gene expression remained largely unchanged, numerous key aspects of VFA fermentation, predominantly carbon exchanges between different VFA, were altered in response to nutrient source. The third investigation described in this work examined the ability of the microbial populations responsible for rumen fermentation to explain variation in beef and dairy cow productivity compared with the ability of diet characteristics to explain this variation. Using statistical methods to analyze the reports currently available in scientific literature, our findings indicate that the rumen microbiome and diet may exert independent effects on productivity levels and that the microbiome may be used to enhance diet-based predictions of animal performance. Finally, we explored variations in the sheep rumen microbiome in response to the diet treatments utilized in Experiment 2. We observed minimal impact of protein source on the microbiome, but numerous microbial responses were evident when fiber source was varied. These responses included decreases of fiber-degrading bacterial populations and increases in pectin-degrading populations when beet pulp was fed compared to timothy hay. Taken together, these experiments help to provide us with a more comprehensive picture of the numerous factors involved in the process of converting feed to a usable form of energy for ruminant livestock.

Two media proposed for the isolation of cellulolytic rumen bacteria were investigated. The inorganic medium containing rumen fluid gave greater total counts, greater cellulolytic counts, and a greater variety of morphological forms of cellulolytic rumen bacteria than the rich organic medium containing no rumen fluid. Cellulolytic bacteria were isolated in the inorganic medium which could not be subcultured in the rich organic medium. No cellulolytic bacteria were isolated in the rich organic medium which could not be subcultured in the inorganic medium containing rumen fluid. On the basis of the data obtained, it was concluded that under the conditions of the investigation the inorganic medium containing rumen fluid is superior to the rich organic medium for the culturing of cellulolytic rumen bacteria and for the culturing of the predominating fora of the rumen. / M.S.

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