Browsing by Author "Condas, Larissa"

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    Distribution of Staphylococcus non-aureus isolated from bovine milk in Canadian herds
    (2016) Condas, Larissa; Barkema, Herman; De Buck, Jeroen; Liljebjelke, Karen; Kastelic, John; Middleton, John; De Vliegher, Sarne; Armstrong, Glen
    The Staphylococci non-aureus (SNA) species are among the most prevalent isolated from bovine milk. However, the role of each species within the SNA group still needs to be fully understood. Knowing which SNA species are most common in bovine intramammary infections (IMI), as well as their epidemiology, is essential to the improvement of udder health on dairy farms worldwide. This thesis is comprised of two studies on the epidemiology of SNA species in bovine milk, and used molecular methods to identify of isolates obtained from the Canadian Bovine Mastitis and Milk Quality Research Network. The first study focused on the prevalence of SNA species on Canadian dairy farms and potential associations of SNA positive mammary quarters with bulk milk somatic cell count (BMSCC), barn type, parity, month of lactation and quarter location. Overall SNA represented 9% of the isolates from culture positive mammary quarters and the most common species were S. chromogenes, S. simulans, S. xylosus, S. haemolyticus, and S. epidermidis. Province and barn type were associated with SNA species distribution; Albertan bedded-packs were mostly affected by S. chromogenes, Maritimes free-stall herds by S. epidermidis, and Ontario and Quebec tie-stalls by S. xylosus. Staphylococcus arlettae, S. cohnii, and S. gallinarum were isolated from quarters of herds with high BMSCC. Fresh heifers and cows in later lactation were most frequently infected by S. chromogenes. The second study focused on the distribution of the same species in SNA positive-quarters according to udder inflammation status, classified according to low and high SCC and clinical mastitis. Average somatic cell count (SCC) for the SNA as a group was 70,000 cells/mL, driven mostly by S. chromogenes, S. haemolyticus, S. xylosus and S. epidermidis. Species-specific prevalence of SNA-positive quarters was higher in high (≥ 200,000 cells/mL) than in low SCC (< 200,000 cells/mL) samples for the 11 most frequently isolated SNA species. Staphylococcus sciuri was more frequently isolated from clinical mastitis samples. Considering SNA as a group will misrepresent the role of individual species on farms. Ultimately, adopting molecular identification of SNA species along with future research in species-specific risk factors are necessary to fully elucidate the importance of of the different SNA species on udder health and possible species-specific interventions.