Theses & Dissertations

Permanent URI for this collection


Recent Submissions

Now showing 1 - 5 of 356
  • Item
    Impacts of Antimicrobials on Host Responses and Gut Microbiome Through Up-regulating the Gut Endogenous Alkaline Phosphatase Expression in Weanling Pigs
    (University of Guelph, ) Chen, Jiali; Fan, Ming
    Administration of prescribed therapeutic antimicrobials for prophylactic purpose is still widely practiced in global swine production to maintain gut health and growth of weanling pigs. Three studies were conducted to comprehensively understand the impact of prescribed therapeutic antimicrobials (mg/kg), including chlortetracycline (220), tiamulin (31.2) and ZnO (2358), on the digestive utilization of dietary fiber, starch and crude fat, endogenous alkaline phosphatase (AP) activity and expression, bacterial species level of the gut microbiome changes and their interrelationships and contributions to growth promotion and gut health in weanling pigs. In Study-1, antimicrobials improved (P<0.05) weanling pig growth performance. The growth-promoting effect of antimicrobials were associated (P<0.05) with increased feed intake and reduced digestive utilization of dietary fiber rather than the unaffected (P>0.05) digestive utilization of starch and crude fat. The full-length 16S rRNA gene sequencing data showed that antimicrobials substantially reduced or eliminated (P<0.05) the cecal digesta and fecal relative abundances of specific bacterial species within Lactobacillus, Streptococcus and zoonotic Campylobacter. Fecal relative abundances of p-1088-a5 sp., Parasutterella sp., Defluviitaleaceae sp., Selenomonas sp., Mitsuokella sp., Lachnoclostridium sp. and Streptococcus orisratti displayed (P<0.05) the potential to serve as non-invasive biomarkers for the prediction of growth performance. In Study-2, antimicrobials up-regulated (P<0.05) the AP maximal enzyme activity (i.e., Vmax) in the gut and plasma. Plasma AP Vmax showed a positive linear correlation (P<0.05) with feed intake and growth rate, suggesting it as a novel biomarker for predicting porcine growth performance. Antimicrobials also demonstrated an improvement (P<0.05) in the gut health of weanling pigs, as indicated by a lower fecal score. Furthermore, antimicrobials increased (P<0.05) the cecal digesta and fecal relative abundances of bacterial endocellulase gene GH5-p4818Cel5_2A. Fecal relative abundances of GH5-p4818Cel5_2A, Blautia obeum, Oribacterium sp., Lactobacillus salivarius, p-2534-18B5 sp., dgA-11 sp., Mucispirillum sp. and Streptococcus orisratti exhibited a linear correlation (P<0.05) with gut health, suggesting their potential roles as biomarkers for predicting porcine gut health. In Study-3, antimicrobials down-regulated (P<0.05) the permeability and inflammation-related gene mRNA abundances in the hindgut which were associated (P<0.05) with growth performance and gut health endpoints as well as abundances of the identified specific bacterial species in weanling pigs.
  • Item
    A mixed methods approach to investigate the outcomes of infant eastern cottontails (Sylvilagus floridanus) in Canadian wildlife rehabilitation centres
    (University of Guelph, ) Kosmal, Pauline; Jacobs, Shoshanah; Cox, Sherri
    Eastern cottontail rabbits (Sylvilagus floridanus) are among the most admitted species to Canadian wildlife rehabilitation centres. Unfortunately, infant eastern cottontails have a guarded prognosis, with little scientific evidence to support why. For this research, a mixed methods approach was used better understand the process of rehabilitating eastern cottontails and how protocols may be revised to better support their health and welfare. The objectives of this research were to: 1) assess the present scientific literature in Canada and the United States (as of 2021) on raising eastern cottontails in rehabilitation and address variations in protocols, 2) analyze survey responses from Canadian eastern cottontail rehabilitators, including details from their 2020 season, rehabilitator backgrounds, information sharing and sourcing, and how this may affect the creation of protocols, 3) assess rehabilitator attitudes and beliefs toward raising eastern cottontails to determine their personal influence on practice, and 4) perform necropsies and histopathological analysis of six to eight tissues (heart, liver, stomach, small intestine, large intestine, cecum, and lungs, lymph node, bladder and/or kidney) from rehabilitated eastern cottontails to determine cause of death in those who died without clinical symptoms. The results of this research suggest eastern cottontail rehabilitators need more research to support successful the release of healthy eastern cottontails – specifically, appropriate release age or weight and release sites, and refinement of feeding protocols – specifically, formula additives and weaning strategies.
  • Item
    The effect of Lactobacillus helveticus supplementation on calf performance and gut health during the pre-weaning and post-weaning period
    (University of Guelph, ) Olmeda, Maria Florencia; Steele, Michael
    Promoting health, growth and well-being of dairy calves is vital to ensure the future of the lactating herd. Thus, preserving their health becomes essential, as it directly contributes to boosting their immune system and maximizing nutrient utilization. Therefore, the objectives of this research were to 1) evaluate the impact of tyndallized Lactobacillus helveticus (TLH) supplementation on growth and health metrics during the pre- and post-weaning period to Holstein calves, and 2) to evaluate if supplementing TLH can mitigate the adverse effects of an abrupt weaning model on gut barrier function and inflammation. Data from Chapter 2 demonstrates that TLH supplementation improves feed intake in the post-weaning period and tends to improve growth, whereas Chapter 3 suggests that TLH leads to a reduction in blood inflammatory-related markers. Based on these data, the use of TLH could enhance the recovery of calves exposed to abrupt weaning practices, promoting their health and performance.
  • Item
    The Effects of Feeding Colostrum Beyond Day One of Life on Dairy Calf Growth, Health, Metabolism, and Gut Barrier Function
    (University of Guelph, ) McCarthy, Hannah; Steele, Michael
    The objective of this thesis was to investigate if supplementing colostrum to calves beyond the first day of life could impact their health, growth, metabolism, and gut permeability during the preweaning period. The first study compared the effects of different colostrum feeding strategies on growth and health factors of preweaning dairy heifers. Replacing part of the milk diet with either 50% colostrum for 2 days or 10% colostrum for 14 days reduced the hazard of diarrhea and mortality, with increased growth at specific time points. The second study investigated the impact of the 14-day 10% colostrum supplementation on metabolism and gut barrier function in preweaning dairy heifers. Overall, colostrum supplementation impacted postprandial insulin kinetics, increasing the concentration and clearance rate of insulin, and reduced gut permeability. In summary, this research provides novel information on the effects of extended colostrum feeding on growth, health, metabolism, and gut permeability in preweaning calves.
  • Item
    Exploring prepartum feed intake and wearable sensor data as predictors of transition health and performance of dairy cows
    (University of Guelph, ) Santos, Matheus; Ribeiro, Eduardo
    The objectives of this thesis were: 1) to evaluate the variability in the modulation of prepartum dry matter intake (DMI) and its associations with transition metabolism, health, and performance; and 2) to assess the associations of rumination time prior to calving with the metabolism, health, and performance of dairy cows. Data on rumination and physical activities and blood metabolites improved the performance of linear models explaining the modulation of prepartum DMI. Cows with a large decline in prepartum DMI were fatter and heavier before calving, had impaired metabolism, but yielded more milk during the first 14 weeks of lactation. Although cows with a low level of prepartum DMI had similar metabolic outcomes, they produced less milk in the subsequent lactation. Regarding objective 2, cows with reduced prepartum rumination time had a challenging transition metabolism, but only multiparous cows were associated with a higher incidence of clinical diseases and impaired performance.