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Thesis (M.S.)--University of Missouri-Columbia, 2006. / "December 2006" The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Includes bibliographical references.

<i>Mycoplasma bovis</i> is generally considered the causative pathogen associated with Chronic Pneumonia and Polyarthritis Syndrome (CPPS) in feedlot cattle. However, <i>M. bovis</i> virulence may vary between strains as it is also isolated from asympytomatic cattle. The following study aims to determine the prevalence of <i>M. bovis</i> in the respiratory tract of western Canadian cattle using two sampling methods and at two time points following feedlot entry. Three study groups were sampled. In the first group nasal swabs (NS) and bronchoalveolar lavages (BAL) were taken from 36 clincally healthy cattle at the University of Saskatchewan feedlot at both 14 and 90 days on feed (DOF). In a second experiment, NS were taken from 56 animals upon arrival at a commercial feedlot and one week to three months later upon treatment for respiratory disease. Lung and joint tissue swabs were collected at necropsy from a third group of 19 animals with CPPS clinical pathology originating in 10 different western Canadian feedlots. All samples were selectively cultured for <i>Mycoplasma</i> spp. DNA was extracted from isolated putative <i>Mycoplasma</i> colonies and amplified with universal 16S rRNA gene primers for identification. Amplified Fragment Length Polymorphism (AFLP) was used to genetically differentiate <i>M. bovis</i> positive isolates. More <i>M. bovis</i> was isolated from NS than BAL and <i>M. bovis</i> prevalence increased with DOF in the feedlot in both the University of Saskatchewan and commercial feedlot trials. Three genetically distinct clusters (A, B, and C) were isolated from the necropsy group. Two of these clusters were primarily associated with isolates collected from feedlot cattle and one strain was exclusively found in CPPS-associated mortalities. No significance difference in the prevalence of <i>M. bovis</i> strains was observed between different days on feed or sampling methods. It was concluded that either the difference in disease state is a host dependent outcome, due to a multi-factorial disease complex, or the AFLP assay was not sensitive enough to differentiate strains based on virulence.

<i>Mycoplasma bovis</i> is generally considered the causative pathogen associated with Chronic Pneumonia and Polyarthritis Syndrome (CPPS) in feedlot cattle. However, <i>M. bovis</i> virulence may vary between strains as it is also isolated from asympytomatic cattle. The following study aims to determine the prevalence of <i>M. bovis</i> in the respiratory tract of western Canadian cattle using two sampling methods and at two time points following feedlot entry. Three study groups were sampled. In the first group nasal swabs (NS) and bronchoalveolar lavages (BAL) were taken from 36 clincally healthy cattle at the University of Saskatchewan feedlot at both 14 and 90 days on feed (DOF). In a second experiment, NS were taken from 56 animals upon arrival at a commercial feedlot and one week to three months later upon treatment for respiratory disease. Lung and joint tissue swabs were collected at necropsy from a third group of 19 animals with CPPS clinical pathology originating in 10 different western Canadian feedlots. All samples were selectively cultured for <i>Mycoplasma</i> spp. DNA was extracted from isolated putative <i>Mycoplasma</i> colonies and amplified with universal 16S rRNA gene primers for identification. Amplified Fragment Length Polymorphism (AFLP) was used to genetically differentiate <i>M. bovis</i> positive isolates. More <i>M. bovis</i> was isolated from NS than BAL and <i>M. bovis</i> prevalence increased with DOF in the feedlot in both the University of Saskatchewan and commercial feedlot trials. Three genetically distinct clusters (A, B, and C) were isolated from the necropsy group. Two of these clusters were primarily associated with isolates collected from feedlot cattle and one strain was exclusively found in CPPS-associated mortalities. No significance difference in the prevalence of <i>M. bovis</i> strains was observed between different days on feed or sampling methods. It was concluded that either the difference in disease state is a host dependent outcome, due to a multi-factorial disease complex, or the AFLP assay was not sensitive enough to differentiate strains based on virulence.

En Amérique du Nord, Mycoplasma bovis est le plus pathogène des mycoplasmes retrouvés chez les bovins. Les principales maladies qu’on lui associe (maladies respiratoires, mammites, arthrites septiques et otites moyennes et/ou internes) constituent un défi à l’industrie laitière à cause de la difficulté à les traiter et à les prévenir par une vaccination. L’objectif principal de ce projet était d’étudier l’excrétion nasale et la réponse sérologique à M. bovis chez les génisses de remplacement, entre la naissance et 7 mois d’âge, dans 4 troupeaux laitiers au Québec. Quatre-vingt-trois paires mère/génisse provenant de 4 cohortes de bovins laitiers étaient prélevées mensuellement (génisses : 0 à 7 mois ; mères : 0, 1 et 5 mois après vêlage). Écouvillons nasaux et échantillons de lait étaient analysés par culture bactériologique et par immunofluorescence indirecte. Les anticorps circulants étaient détectés par le test ELISA. À la naissance, la prévalence sérologique des génisses était supérieure à celle des mères (P = 0,01). La transmission de M. bovis aux génisses par le lait et par l’excrétion nasale des mères était faible. L’âge moyen (jour) d’une génisse à sa 1ère excrétion nasale et sa 1ère séroconversion à M. bovis était loin de la période néonatale: 77,5 ± 11,2 (n = 22) et 96,8 ± 7,4 (n = 36) respectivement. Conclusion, les vaches adultes n’ont constitué qu’une voie mineure de transmission de M. bovis aux génisses, la principale voie de transmission était fort probablement le contact direct ou indirect avec d’autres génisses excrétrices nasales de M. bovis. / In North America, Mycoplasma bovis is the most pathogenic mycoplasma found in cattle. The main diseases associated with it (respiratory disease, mastitis, septic arthritis and otitis median and/or internal) are a challenge to the dairy industry because of the difficulty to treat them and to prevent them by vaccination. The principal objective of this project was to study nasal shedding and serological response to M. bovis in replacement heifers, between birth and 7 months of age, in four dairy herds in Quebec. Eighty three pairs cow/heifer in 4 cohorts of dairy cattle were sampled monthly (heifers: 0 to 7 months; cows: 0, 1 and 5 months after calving). Nasal swabs and milk samples were analyzed by bacteriological culture and by indirect immunofluorescence. Circulating antibodies were detected by ELISA test. At birth, the serologic prevalence of heifers was significantly higher than the serologic prevalence of cows (P = 0,01). Transmission of M. bovis to heifers in milk and nasal shedding from cows was low. The average age (days) of a heifer for first nasal shedding and first seroconversion to M. bovis was far from the neonatal period: 77,5 ± 11,2 days (n = 22) and 96,8 ± 7,4 days (n = 36) respectively. Conclusion, cows were only a minor route of transmission of M. bovis to heifers, the main route of transmission was most likely the direct or indirect contact with other heifers shedding M. bovis in their upper respiratory tract.

En Amérique du Nord, Mycoplasma bovis est le plus pathogène des mycoplasmes retrouvés chez les bovins. Les principales maladies qu’on lui associe (maladies respiratoires, mammites, arthrites septiques et otites moyennes et/ou internes) constituent un défi à l’industrie laitière à cause de la difficulté à les traiter et à les prévenir par une vaccination. L’objectif principal de ce projet était d’étudier l’excrétion nasale et la réponse sérologique à M. bovis chez les génisses de remplacement, entre la naissance et 7 mois d’âge, dans 4 troupeaux laitiers au Québec. Quatre-vingt-trois paires mère/génisse provenant de 4 cohortes de bovins laitiers étaient prélevées mensuellement (génisses : 0 à 7 mois ; mères : 0, 1 et 5 mois après vêlage). Écouvillons nasaux et échantillons de lait étaient analysés par culture bactériologique et par immunofluorescence indirecte. Les anticorps circulants étaient détectés par le test ELISA. À la naissance, la prévalence sérologique des génisses était supérieure à celle des mères (P = 0,01). La transmission de M. bovis aux génisses par le lait et par l’excrétion nasale des mères était faible. L’âge moyen (jour) d’une génisse à sa 1ère excrétion nasale et sa 1ère séroconversion à M. bovis était loin de la période néonatale: 77,5 ± 11,2 (n = 22) et 96,8 ± 7,4 (n = 36) respectivement. Conclusion, les vaches adultes n’ont constitué qu’une voie mineure de transmission de M. bovis aux génisses, la principale voie de transmission était fort probablement le contact direct ou indirect avec d’autres génisses excrétrices nasales de M. bovis. / In North America, Mycoplasma bovis is the most pathogenic mycoplasma found in cattle. The main diseases associated with it (respiratory disease, mastitis, septic arthritis and otitis median and/or internal) are a challenge to the dairy industry because of the difficulty to treat them and to prevent them by vaccination. The principal objective of this project was to study nasal shedding and serological response to M. bovis in replacement heifers, between birth and 7 months of age, in four dairy herds in Quebec. Eighty three pairs cow/heifer in 4 cohorts of dairy cattle were sampled monthly (heifers: 0 to 7 months; cows: 0, 1 and 5 months after calving). Nasal swabs and milk samples were analyzed by bacteriological culture and by indirect immunofluorescence. Circulating antibodies were detected by ELISA test. At birth, the serologic prevalence of heifers was significantly higher than the serologic prevalence of cows (P = 0,01). Transmission of M. bovis to heifers in milk and nasal shedding from cows was low. The average age (days) of a heifer for first nasal shedding and first seroconversion to M. bovis was far from the neonatal period: 77,5 ± 11,2 days (n = 22) and 96,8 ± 7,4 days (n = 36) respectively. Conclusion, cows were only a minor route of transmission of M. bovis to heifers, the main route of transmission was most likely the direct or indirect contact with other heifers shedding M. bovis in their upper respiratory tract.