Abstract
The purpose of this study was to evaluate whether the risk of Streptococcus uberis clinical mastitis at cow level could be predicted from the historical presence of specific strains of S. uberis on dairy farms. Matrix-assisted laser desorption ionization time of flight mass spectrometry was used to identify S. uberis isolates potentially capable of contagious transmission. Data were available from 10,652 cows from 52 English and Welsh dairy farms over a 14 month period, and 521 isolates of S. uberis from clinical mastitis cases were available for analysis. As well as the temporal herd history of clinical mastitis associated with particular S. uberis strains, other exposure variables included cow parity, stage of lactation, milk yield, and somatic cell count. Observations were structured longitudinally as repeated weekly measures through the study period for each cow. Data were analyzed in a Bayesian framework using multilevel logistic regression models. Similarity of mass spectral profiles between isolates of S. uberis from consecutive clinical cases of mastitis in herds was used to indicate potential for contagious phenotypic characteristics. Cross validation showed that new isolates with these characteristics could be identified with an accuracy of 90% based on bacterial protein mass spectral characteristics alone. The cow-level risk in any week of these S. uberis clinical mastitis cases increased with the presence of the same specific strains of S. uberis in other cows in the herd during the previous 2 weeks. The final statistical model indicated there would be a 2–3 fold increase in the risk of S. uberis clinical mastitis associated with particular strains if these occurred in the herd 1 and 2 weeks previously. The results suggest that specific strains of S. uberis may be involved with contagious transmission, and predictions based on their occurrence could be used as an early warning surveillance system to enhance the control of S. uberis mastitis.
Highlights
Mastitis control is of considerable importance to dairy producers in terms of potential economic, environmental, and welfare constraints (Hospido and Sonesson, 2005; Halasa et al, 2007; Kemp et al, 2008)
New intramammary infections are thought to arise from a reservoir of pathogens either in the environment, or other cows (Leigh, 1999; Barkema et al, 2009), and for the common mastitis pathogen, Streptococcus uberis, transmission is thought possible through both routes (Zadoks et al, 2003; Rato et al, 2008)
With the final classification for S. uberis clinical mastitis cases based on differences in protein mass spectra alone, internal recognition of the 69 contagious MALDI-TOF MS profile’ (CMP) isolates from 64 cows used in model training was 97%, and for the 54 environmental MALDI-TOF MS profile’ (EMP) isolates from 50 cows used for comparison, internal recognition was 81%
Summary
Mastitis control is of considerable importance to dairy producers in terms of potential economic, environmental, and welfare constraints (Hospido and Sonesson, 2005; Halasa et al, 2007; Kemp et al, 2008). In order to control mastitis, the risk pathways. For control strategies to be effective and efficient in terms of utilising resources, farm-specific intervention plans have been shown to perform well (Green et al, 2007), dependent on ongoing mastitis control efforts. An alternative approach could be to target control efforts towards high risk periods, if these could be identified in advance. This would allow herd managers to ensure control policies are effectively enhanced when most needed. New intramammary infections are thought to arise from a reservoir of pathogens either in the environment, or other cows (Leigh, 1999; Barkema et al, 2009), and for the common mastitis pathogen, Streptococcus uberis, transmission is thought possible through both routes (Zadoks et al, 2003; Rato et al, 2008)
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