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Typewritten

No abstract / Thesis (PhD)--University of Pretoria, 1942 / Includes bibliographical references (leaves 127-132). / Original document: Typescript / Production Animal Studies / PhD / Unrestricted

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Bibliography: leaves 175-196. The influence of starch in grain-based diets on fat development in cattle and sheep is investigated.

Includes bibliographical references (leaves 175-196). / xii, 196 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The influence of starch in grain-based diets on fat development in cattle and sheep is investigated. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1995

The objective of this study was the evaluation of grass silage made from P. maximum cv. Gatton (P. maximum) and Digitaria eriantha spp. eriantha (Smutsfinger) grass. The study was conducted in two phases. In phase one the influence of sugar (molasses) addition, wilting, growth stage and plant species, on the quality of the silages obtained, were investigated. Three growth stages were incorporated, an early (physiologically young), medium (boot) and late (full bloom) stage. Four different treatments were applied during ensiling, namely direct cut, direct cut + sugar, wilted and wilted + sugar. The second phase comprised of a partial digestibility study to evaluate the differences between plant species and growth stage, within a specific treatment. The silages used were made from the medium and late growth stages, where prior wilting and sugar addition occurred. The addition of sugar during ensiling, even with prior wilting, had a positive effect on silage quality, leading to a lower pH, ammonia-nitrogen concentration and a higher lactic acid concentration in the silage. These effects were less pronounced with the plant material ensiled at a late growth stage. These silages tended to undergo secondary fermentation between day 21 and day 120, when sugar was added. When comparing the three growth stages, within the direct cut + sugar and wilted + sugar treatments, the following was observed. The silages made from early and medium growth stages tended to be of better quality compared to the silages made from the late growth stage. In most of the comparisons the silages made from the medium growth stage were of a better quality than that of the silages made from the younger plant material. In the comparison between P. maximum and D. eriantha silages, the silages made from P. maximum grass tended to be of a better quality than that made from D. eriantha grass. The difference between the two species was smaller than the differences observed between growth stages within a specie. In the partial digestibility study, there was a difference in OMI, with sheep receiving the late growth stage silages having higher intakes. When expressed as DOMI / W0.75 no significant differences were observed between the four diets. There were no significant differences in the total digestibility of OM across the four diets. There were differences in the rumen ammonia and VFA's concentrations across the diets. There was a significant difference in the intake of nitrogen across the four diets, resulting in differences in the disappearance of nitrogen, ammonia and non-ammonia-nitrogen across the four diets. There was no difference in the total true nitrogen digestibility across the four diets. / Dissertation (MSc Agric (Animal Nutrition))--University of Pretoria, 2006. / Animal and Wildlife Sciences / unrestricted

Antigen-specific and polyclonal serum immunoglobulin G (IgG) concentrations were measured in control (Con), vitamin A-deficient (A-def), and vitamin A-repleted (A-rep) lambs. In Trial, I ewe lambs were injected with primary and secondary antigenic challenges of ovalbumin (1mg) and lysozyme (.1mg). The A-def lambs were then repleted with vitamin A and all lambs were injected with primary and secondary antigenic challenges of human gamma globulin (HGG) (.1mg). In Trial II Con and A-def wether lambs were given primary and secondary antigenic challenges of ovalbumin (20μg). Half of the A-def lambs were then repleted with vitamin A. All lambs were subsequently given a primary and secondary challenge of HGG (20 μg). Spleen wt were similar for all treatments in Trial I while A-def V lambs in Trial II had greater spleen wt (P<.01) than Con or A-rep lambs. Polyclonal serum IgG concentrations were unaffected by treatment in Trial I while in Trial II concentrations were greater (P<.05) in the A-def lambs during the HGG challenge period. Antigen-specific IgG concentrations in both trials tended to be greater in the Con lambs towards the end of both the ovalbumin (Trial I and II) and lysozyme (Trial I) challenge periods. Control and A-rep lambs in Trial I responded similarly to the HGG challenges. In Trial II both the A-def and A-rep lambs had lower (P<.10) HGG specific serum IgG concentrations on the last 3 wk of the HGG challenge period as compared to A-def lambs. Humoral immune function appears to be impaired in A-def lambs and a 2-wk repletion period was not sufficient in this study to restore humoral immune function to normal levels. / Ph. D.