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No description available.

The purpose of this study was to describe the herd antibody status to Salmonella Typhimurium as estimated from co-mingled milk samples and to describe the resulting geographical patterns found in Texas dairy herds. Bulk tank milk samples were collected from 852 Grade A dairies throughout Texas during the summer of 2001. An indirect enzyme-linked immunosorbent assay (ELISA) using S. Typhimurium lipopolysaccharide was performed with signal to noise ratios calculated for each sample. The ELISA ratio was used in fitting a theoretical variogram and kriging was used to develop a predicted surface for these ratios in Texas. A spatial process with areas of higher risk located in the panhandle and near Waller County was apparent. Lower risk areas included Atascosa, Cooke, Collin, Titus, Comanche and Cherokee Counties. Subsets representing large dairy sheds in northeast Texas, the Erath County area, and the Hopkins County area were also evaluated individually. Each result illustrated a spatial process with areas of low and high ELISA ratio predictions. Cluster analysis was performed for the entire state with cases defined as herds having milk ELISA ratios greater than or equal to 1.8. Using this cutoff, the prevalence of herds with positive bulk tank milk ELISAs was 4.3%. Significant clustering of cases was demonstrated by the Cuzick and Edward's test. The spatial scan statistic then identified the two most likely clusters located in and near the Texas Panhandle. This study demonstrated that the distribution of S. Typhimurium antibodies in bulk tank milk in Texas is describable by a spatial process. Knowledge of this process will help elucidate geospatial influences on the presence of S. Typhimurium in dairy herds and enhance our understanding of the epidemiology of salmonellosis.

No description available.

No description available.

No description available.

This thesis was conducted to investigate risk factors for ketosis development in lactating dairy cattle and evaluate treatments for affected animals. Four main studies were carried out. A systematic review of the ketosis treatment literature was performed to analyze the current body of literature available and provide guidance for treatments to be used in future studies. Secondly, a randomized clinical trial was performed on seventeen commercial dairy farms to determine the effectiveness of a combination butaphosphan cyanocobalamin product, insulin, and propylene glycol for ketosis treatment. A second randomized clinical trial was performed on nine commercial dairy herds to further evaluate the usefulness of a combination butaphosphan cyanocobalamin product and two durations of propylene glycol treatment on ketosis resolution and early lactation milk production. Finally, records from five commercial dairy farms were analyzed to evaluate individual cow risk factors associated with ketosis development. Evaluation of the ketosis treatment literature revealed the lack of well-designed ketosis treatment studies and the need for further investigation to determine an effective treatment regimen. Both treatment trials showed an effect of blood glucose concentrations at the time of enrollment on the efficacy of study treatments that had not been previously described in the literature. Animals that had blood glucose < 2.2 mmol/L at the time of ketosis diagnosis were more likely to cure and produced more milk when treated with insulin, butaphosphan cyanocobalamin, or extended duration of propylene glycol than untreated controls with blood glucose < 2.2 mmol/L. Treatment benefits did not extend to animals with blood glucose > 2.2 mmol/L at the time of enrollment. Older age at first calving, extended days open in the previous lactation, longer dry period, and increased parity increased ketosis risk. Also, animals that were ketotic during a lactation were more likely to become ketotic in the subsequent lactation. The information contained in this thesis helps increase understanding of ketosis risk and proper treatment. The novel interaction of the level of blood glucose and ketosis sheds light on previous inconsistent results on ketosis impacts and will change approaches to understanding and treatment of the condition in the field. / Ontario Ministry of Agriculture and Food, Bayer Animal Health, Vetoquinol, American Association of Bovine Practitioners Research Assistantship

Two clinical studies were conducted to evaluate the effects of recombinant bovine somatotropin in daily, weekly or bi-weekly injected preparations on milk yield, feed efficiency and reproduction. In the first study, a linear dose-response effect of recombinant bST on milk yield with doses of up to 150 mg &middot; 7d-1 was observed. Feed intake was not affected and feed efficiency was increased by bST during lactation. Body condition at the end of lactation was lower in cows supplemented with bST. Feed intake during the dry period following bST supplementation was not affected by bST given during lactation. When differences in body condition were taken into account, efficiency of conversion of dietary energy to milk energy was not affected by bST supplementation. In another study of bST supplementation during lactation, a daily dose of 10.3 mg &middot; d-1 and a sustained release formulation of 350 mg &middot; 14d-1 did not increase milk production or feed efficiency. In the absence of a milk production response, reproductive performance was not affected by bST supplementation. Progesterone production in the second oestrous cycle post partum was higher in cows receiving bST but oestrous activity was not affected. Body condition at calving did not affect milk production, response to rbST or reproductive performance. Cows calving with a body condition less than 3.25 consumed more feed per unit of body weight and resumed ovarian cyclic activity later than cows calving with a body condition greater or equal to 3.25. An epinephrine challenge during the dry period was performed to evaluate whether the effects of bST supplementation during lactation on adipose tissue metabolism persisted during the dry period. Lipid mobilisation by cows having received bST during lactation, as described by the release of non-esterified fatty acids following the epinephrine challenge, did not differ from control cows. Two studies designed to evaluate the effect of bST on oestradiol-induce