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Browsing Graduate Studies by Subject "16S rRNA sequencing"
(2018-07-12) Stroebel, Christina Maria; Timsit, Édouard; Alexander, Trevor W.; De Buck, Jeroen M.; Janzen, Eugene D.
Commingling at auction markets is considered a major predisposing factor for bacterial bronchopneumonia (BP) in beef cattle. However, the effects of commingling on the respiratory tract bacterial communities is largely unknown. Therefore, the objective of the thesis was to study the effects of transportation to and commingling at an auction market on the nasopharyngeal and tracheal bacterial communities of recently weaned calves using culture-dependent and independent methods. Two groups of 30 Angus-cross heifers were studied from weaning at the ranches of origin to 28 d after arrival at a feedlot. For each group, half the heifers were either transported directly to a feedlot after weaning (RANC) or transported to and commingled at an auction market for 24 hrs before being placed in a feedlot (AUCT). Heifers from both groups received vaccines against major respiratory viruses and a parenteral injection of a long acting macrolide (tildipirosin) at on-arrival processing (d2). Deep nasal swabs (DNS) and trans-tracheal aspirates (TTA) were collected at weaning (d0) and at on-arrival processing at the feedlot (d2). Deep nasal swab sampling only was then repeated 7 days (d9) and 28 days (d30) after arrival. Bacterial culture and 16S rRNA sequencing did not reveal difference in the nasopharyngeal and tracheal bacterial communities between RANC and AUCT at any sampling days. However, both time after arrival and feedlot where calves were placed affected diversity and composition of the nasopharyngeal bacterial communities. In both groups, there was a reduction in bacterial diversity and a large increase in Mycoplasma after feedlot placement, especially seven days after on-arrival processing. Furthermore, we observed the horizontal transmission of a multi-resistant strain of Pasteurella multocida among calves at d9 and d30 in one of the two groups of heifers. Based on these findings, we concluded that transportation to and commingling at an auction market for 24 hrs did not significantly influence the composition and diversity of the nasopharyngeal and tracheal bacterial communities of recently weaned calves.