Characterisation of preweaning dairy calf respiratory disease in Irish dairy farms with focus on the relationship between housing environment and respiratory disease prevalence
Year: 2024
Type: dissertation
Abstract: Bovine respiratory disease (BRD) is one of the major health challenges to dairy calves globally. The seasonal calving production system found in Ireland is thought to be no different, however there is very little published data with regard to the epidemiology of BRD in Ireland. Prior to the undertaking of this work, the actual calf level prevalence of BRD had not been estimated in a seasonal calving dairy system, nor had the diagnostic performance of commonly used methods of BRD diagnosis such as thoracic ultrasound (TUS) or clinical respiratory scoring (CRS) been estimated. One of the key risk factors for BRD in preweaning dairy calves is thought to be the housing environment; this has been investigated to some extent but not in a climate similar to Ireland. Therefore, the aims of this thesis is to first estimate the prevalence of BRD on Irish dairy farms. The second aim of this work was to establish the diagnostic performance of CRS systems in an Irish context. The third aim of this work was to further investigate the risk factors associated with BRD in preweaning calves with a specific focus on the interaction between housing environment and BRD. To achieve these aims 98 farms were recruited, these farms were visited once prior to the calving season and once during the calving season. At the first visit, the calf housing and calf management practices were surveyed. A data logger was also installed in the calf housing. At the second visit, 20 calves were examined using TUS and CRS, microbial air samples were taken and the calf housing environment was characterised. For this work we used a hierarchical Bayesian latent class model (HBLCM) to estimate the calf level prevalence of BRD. We also estimated the diagnostic performance of TUS and CRS using HBLCM. We found that the calf level prevalence of BRD was approximately 4%, which was lower or similar to international estimates. The diagnostic performance of TUS and CRS was similar to that estimated in other publications, however it was clear that the interpretation of CRS impacted on the diagnostic performance of the tests. To gain a better understanding of the relationship between housing environment and BRD we undertook two tasks; an analysis of the housing environment and management of the farms visited and a systematic review. The systematic review found weak, and in some cases, conflicting results with regard to the relationship between housing environment and BRD. The analysis in this work highlighted that both high and low temperatures play a role in BRD prevalence, and a relationship between air microbial characteristics and BRD was also evident. This also highlighted the relationship between housing design (inlet and outlet design) and BRD prevalence. The findings from this work are significant because they highlight the differences in the epidemiology of BRD in seasonal calving dairy herds. In particular they highlight the detrimental effect of both high and low temperatures on a calf’s respiratory health and the impact of housing design, both areas which had not previously been documented.
Author: Donlon, John
Language: English
Subfield: Microbiology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7152339534