2016-06-272016-06-272016-052016-05May 2016http://hdl.handle.net/2346/67086Enteric disease continues to account for a large proportion of morbidity and mortality among dairy calves in the first few weeks of life. After the first 48 hours of life until weaning, approximately 10% of calves die. There are many enteric pathogens that cause severe local and systemic disease with high risk of mortality. In the past, metaphylactic use of antibiotics was widely used in the dairy industry, but lately there has been increased concern in the metaphylactic use of antibiotics. Because of this, there is interest in finding alternatives to antibiotic use that show similar efficacy as antibiotics in reducing disease. Yeast products, specifically those derived from Saccharomyces cerevisiae, have been shown to improve performance and health characteristics in calves. The three Saccharomyces cerevisiae derived products of interest in this research are: Yeast cell wall, yeast culture, and live yeast supplements. In the first study, the effects of yeast culture were studied in Holstein dairy calves infected by Citrobacter freundii. These bacteria are opportunistic pathogens that are common in neonatal animals. Yeast culture was supplemented to calves in the milk (SmartCareTM; SC) and calf starter (XPCTM; XPC). Treatments in the study were: CON: milk replacer and calf starter with no added yeast fermentation products; SC: milk replacer with 1 g SC/calf/d and base calf starter; and SC+XPC: milk replacer with 1 g SC/calf/d and calf starter with 0.5% XPC. Calves in the SC treatment had less signs of infection, indicated by reduced neutrophil to lymphocyte ratios and lowered fecal scores after the Citrobacter freundii challenge. The SC+XPC calves had increased calf starter consumption and ADG after the Citrobacter freundii challenge, and also had reduced neutrophil to lymphocyte ratios and fecal scores after the Citrobacter freundii challenge. The results of the study indicate that calves supplemented with yeast culture had improved performance, health, and risk of scours during neonatal life. In the second study, the effects of yeast culture were studied in Holstein dairy calves infected by Salmonella enterica serotype Typhimurium. Salmonella enterica is one of the more common enteric pathogens found on dairies in the United States, and is the cause of many calf deaths. Yeast culture was supplemented to calves in the milk (SmartCareTM; SC) and calf starter (XPCTM; XPC). Treatments in the study were: CON: milk replacer and calf starter with no added yeast fermentation products; SC: milk replacer with 1 g SC/calf/d and base calf starter; and SC+XPC: milk replacer with 1 g SC/calf/d and calf starter with 0.5% XPC. The SC treatment calves had greater calf starter consumption and reduced fecal shedding of Salmonella enterica. The SC+XPC treatment calves had improved calf starter consumption, greater ADG, reduced neutrophil to lymphocyte ratio, reduced hematocrit, less hemoglobin concentration, and reduced Salmonella enterica shedding after being challenged with Salmonella enterica. These results indicate that both SC and SC+XPC improved performance and enteric health, with the combination treatment having the greatest beneficial effects. In the third and final study, the effects of supplementing milk replacer with SafmannanTM (SM) and ActiSafTM (AS) on calf health and performance throughout the pre-weaned and immediate post-weaned periods were studied. Calves were randomly assigned to treatments that included; CON: milk replacer with no added supplements; SM: milk replacer with 5g SM/calf/d; SM + AS: milk replacer with 2g SM/calf/d and 3g AS/calf/d. The SM calves had reduced leukocyte and neutrophil counts on d 10 and 28 of the study when compared to Con calves, indicating limited pathogenic bacterial exposure. The SM calves had the greatest expression of neutrophil L-selectin an also had greater percentages of neutrophils phagocytizing and producing an oxidative burst on d 28, indicating “priming” of the immune system. The SM + AS calves had increased calf starter consumption in the first weeks of the study. The least number of calves scoured throughout the study in the SM + AS treatment group. Like the SM calves, total leukocyte counts and neutrophil counts were also reduced in the SM + AS calves on d 10, when compared to Con calves. These data suggest that both yeast supplementation strategies may aid in the growth and health of pre-weaned, Holstein calves, with the SM + AS treatment having a more profound positive effect on performance and gastrointestinal health, the SM treatment having a more positive effect on neutrophil activity, and both yeast products having a positive effect on circulating white blood cell numbers.application/pdfengCalfYeastImmunologyThesis2016-06-27Unrestricted.