No description available.

No description available.

The effect of altering dietary protein supply and forage type on milk production, the efficiency of converting dietary nitrogen (N) into milk protein, nutrient digestibility and the splanchnic flux of nutrients was measured using a 2 x 3 factorial design experiment. Six Holstein dairy cows in mid-late lactation, surgically prepared with a rumen fistula and splanchnic blood sampling catheters were fed ad libitum in equal meals provided hourly, total mixed rations consisting of a 50:50 mixture (dry matter (OM) basis) of forage:concentrate, with the forage comprised of either 25:75 or 75:25 grass:maize silage. Rations were formulated to contain dietary protein concentrations of 12.5, 15.0 and 17.5% diet OM providing metabolisable protein below, near, and above estimated requirement. The experiment was conducted as repeated 3 x 3 Latin Squares with 21 d treatment periods, with the effect of protein level tested within squares and forage source as the square effect. Dry matter intake, (OMl), N intake, milk yield and milk N yield increased with increasing dietary protein but were not different between forages. Efficiency of N utilisation decreased with increasing dietary protein and was not different between forages. Rumen ammonia concentrations increased with increasing dietary protein, and were higher when the grass-based diet was fed as N intake was higher for the grass-based diet. Arterial urea concentration and liver urea production increased with increasing dietary protein concentration. Liver release of glucose and Bhydroxybutyrate increased linearly as DMI increased. The net flux of amino acids (AA) were unaffected by dietary treatment, although arterial concentrations of individual essential AA and many nonessential AA increased with increasing dietary protein. The splanchnic flux of AA did not follow results seen for N intake and highlight the complexities of splanchnic metabolism as an integrator of supply and demand by other body tissues.

Experiments were carried out in order to determine the effects of level and form of dietary zinc (Zn) on performance, health and digestibility in dairy cows and metabolism in vitro. In experiment 1, four concentrates vere formulated to provide cattle with recommended level of Zn in either an organic (Bioplex Zn; Alltech Inc., Nicholasville USA) or inorganic (zinc oxide (ZnO); Rumenco, Staffordshire, UK) form or 0.66 of the recommended level again in either form. By supplementing Zn at the recommended level with background levels in the basal diet taken into consideration, a reduction in SCC and milk amyloid A was observed compared to the lower level, whilst supplementing in an organic form at the recommended level increased milk yield. Experiment 2 used the same basal ration and concentrates as experiment 1 to assess the effects of level and form of Zn on digestion and apparent absorption.

No description available.

Body condition score has been considered an indirect measure of nutritional status and nutrition has been demonstrated to interact with reproduction. Adiponectin and leptin, because of its insulin sensitising actions and their association with body condition could be potential regulators of metabolism during the transition from pregnancy to lactation. The work described in this PhD project was designed to investigate the role of metabolic, body condition, and dietary factors in regulation of productive and reproductive performance in dairy cows, with particular regard to glucose homeostasis and adipokines. A special focus was directed to circulating adiponectin and its association with metabolic and hormonal status, and reproduction. Interestingly, adiponectin was found to be present in bovine milk at concentrations similar those of plasma. Body condition score, GH, insulin, leptin, and adiponectin showed a potential to modulate glucose homeostasis and reproductive output. Results from this study demonstrated a negative effect of long-term moderately elevated insulin concentration on reproductive performance. Additionally, BCS at calving and ΔBCS are determinant factors influencing postpartum reproductive recovery and they should be basic components of farming monitoring schemes. Although further investigation is needed to address the proposed negative relationship between adiponectin and GH, and to identify other dietary factors that may modulate circulating adiponectin, data from this study support regulatory roles of adiponectin in metabolism and reproduction. Moreover, adiponectin holds great promise to serve as a putative target molecule that integrates metabolism, reproduction and feeding behaviour. More importantly, hypoadiponectinemia could be another alternative mechanism that contributes to poor fertility in dairy cows. The incorporation of this new knowledge into the development of better nutritional strategies is a key point that is being considered to improve the welfare, and reproductive and productive performance in dairy cows.

Automatic sampling and analysis of milk composition for on-line metabolic profiling has been proposed as a means of monitoring individual cows to detect and correct problems in nutritional management. Acetone, urea, fat, protein and citrate in milk were investigated independently and jointly as potential indicators for monitoring the dairy cow. A series of experiments and milk analysis were conducted to investigate sources of variation within and between cows, nutritional effects on milk composition and whether dietary changes could be detected through changes in milk composition. Novel methods for on-line acetone and urea analysis were also tested. Significant diurnal variation was found in fat, acetone and urea but not in citrate or protein. Acetone and citrate were the most variable constituents; day-to-day variation was 64.3% of mean acetone and 16.4% of mean citrate. Between cow variation was significant in all milk constituents monitored, in terms of means and normal concentration ranges, highlighting the need for individual cow management. Individual variation could be determined by establishing normal ranges of milk constituents for each cow, so that deviations from normal can be detected. Dietary changes at the group and individual cow levels were not detectable and individual responses to dietary changes were unpredictable. Changing the starch to fibre ratio in the diet had no effect on milk acetone and effects on urea, fat and protein were only significant when dietary changes were extreme. Energy output, in terms of FCM, was more closely correlated with fat: protein ratio (R2=0.3) than with acetone (R2=0.006), so the use of acetone as an indicator of metabolic status is inconclusive. Further research on a larger scale is needed to determine whether on-line monitoring will be feasible for nutritional management and economically justified in practice.

The importance of nutrition on reproductive performance is well recognised. However,the mechanisms and specific factors regulating their interaction are still poorly understood. Interest has recently intensified, as fertility in dairy cows has declined. There is a body of evidence on the negative effects of reduced body condition, the high levels of energy and protein intake, however, the results are inconsistent between studies and the role of specific factors, such as insulin and leptin, in the regulation of ovarian function in cattle remains unclear. The main objective of this thesis, therefore, was to test the effects of animal body composition, planes of nutrition and diet composition with emphasis on endocrine and metabolic factors, including progesterone, oestradiol, insulin, IGF-I and leptin, on oocyte quality and early embryo development in cattle. This thesis has demonstrated that alterations in planes of nutrition (Maintenance (M) vs twice maintenance (2M)) affected oocyte quality, and that the effects were dependent on animal body condition score (BCS) (Low vs Moderate). Whilst high (2M) levels of feeding were beneficial for oocytes from animals in Low BCS, they were detrimental to oocyte quality for animals in Moderate BCS. Furthermore, the combination of feeding level and animal BCS created low (10 ull.J/ml), moderate (20 ).lIU/ml) and high (40).lIU/ml) plasma insulin concentrations. Inevitably, however, it also led to the creation of three corresponding levels of plasma leptin concentrations (low: 2 ng/ ml, moderate: 4 ng/ml, and high: 7 ng/ml), indicating that the effects of these metabolic hormones on ovarian function cannot be separated in vivo. However, there was no correlation between changes in metabolic hormones and oocyte quality, suggesting that other endocrine or metabolic factors, not recorded in this study, may be involved in determining the post-fertilisation developmental competence of oocytes. Animal body composition also played an important role in the dietary-induced modifications to oocyte developmental competence both in vivo and in vitro. Indicated by post-fertilisation development in vitro, oocyte quality was enhanced in Low BCS heifers offered the Fibre than the Starch based diets (43.6 vs 24.6% blastocysts for Fibre vs Starch diet), whereas inclusion of protected lipid reduced oocyte developmental competence (27.7 vs 42.9% blastocysts for presence vs absence of Megalac). However, in Moderate BCS heifers, diet composition had litde effect on oocyte quality. Although dietary treatments had little effect on endocrine profile, elevated plasma leptin concentrations were consistently correlated (P<0.001) with increased animal body fatness. The effects of dietary treatments on oocyte maturation in vivo, however, varied from those observed when sera from these animals were used during the final stages of oocyte maturation in vitro, and during early embryo development. These findings suggest that while some diets may be beneficial to oocyte development, they could have a negative effect on embryo quality and subsequent survival. Interestingly, serum harvested from Low BCS heifers enhanced blastocyst formation in vitro compared to serum from heifers in Moderate BCS (24.2 vs 19.0%). This indicates that animal BCS is an important factor involved in the regulation of not only oocyte quality, but also early embryo development. The reasons for these discrepancies between BCS groups, however, remain unknown. Finally, this thesis produced an interesting and novel insight into the nutritional regulation of the lipid content and fatty acid composition of bovine plasma, granulose cells (GCs) and cumulus-oocyte complexes (COCs), and also the effects of serum from contrasting nutritional backgrounds on the lipid content and fatty acid composition of embryos. In general, the inclusion of supplemental fatty acids in the diet significantly increased the lipid content of all tissues tested. The fatty acid composition of COCs and embryos, however, was not correlated with their quality. Nevertheless, differences in the fatty acid composition of plasma, GCs and COCs indicated that there is a selective mechanism of fatty acid uptake by the follicle compartment, which has a preference for saturated fatty acids. The importance and function of specific fatty acids in determining oocyte and embryo quality remain to be elucidated. This thesis has therefore demonstrated that animal body composition is an important factor determining the effects of feeding level and diet composition on oocyte and early embryo development. In summary, high levels of feeding and the Fibre based diets can enhance oocyte quality in thin, but not in moderately fat animals. Alterations in plasma insulin and leptin concentrations did not appear to be correlated with oocyte quality in the present studies, indicating that other factors, not monitored in this project, are possibly involved in the regulation of oocyte developmental competence.

In einer vergleichenden Studie sind Haltungssysteme mit Einzel- und/oder Gruppenabkalbeboxen betrachtet worden. Anhand von Verhaltensbeobachtungen, Cortisol- und Estradiolgehalten im Blut, bakteriologischen Befunden, Gesundheits-, Fruchtbarkeits- und Leistungsparametern wurde der Effekt der unterschiedlichen Haltung zur Kalbung bewertet. Das Einzelhaltungsverfahren stellte sich für Kuh und Kalb als unproblematisch dar. Der direkte Vergleich der Abkalbung in Gruppe oder einzeln in einer Herde zeigte keinen Unterschied in den bewerteten Parametern. Die beim Einzelhaltungsverfahren höhere Kontrolldichte führte zu einer deutlichen Reduzierung von erkrankungsbedingten Kuhabgängen in der Frühlaktation. Die Veröffentlichung richtet sich an Landwirte, Tierärzte, Stallplaner und -ausrüster.

Includes 6 reprints of papers by the author / Includes bibliographical references. / 147 leaves + [51] leaves : ill. (some folded) ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Genetics, 1969