Barlow, John W., White, L. J., Zadoks, Ruth N. and Schukken, Ynte H.. (2009) A mathematical model demonstrating indirect and overall effects of lactation therapy targeting subclinical mastitis in dairy herds. Preventive Veterinary Medicine, Vol.90 (No.1-2). pp. 31-42. ISSN 0167-5877

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Abstract

A deterministic state-transition model for mastitis transmission was developed to explore population level effects of antibiotic treatment regimens targeting chronic subclinical mastitis caused by major gram-positive pathogens in lactating dairy cows. Behavior and sensitivity of model outputs to changes in key parameters were explored. Outcomes included the size of the state variables describing proportions of infected quarters and basic and effective reproductive numbers. Treatment effects were estimated by calculating proportional reductions in state variables at equilibrium for populations implementing a treatment program relative to populations with no intervention. In general the relationships between parameters were complex and non-linear, although the model outputs were especially sensitive to changes in the value of the transmission rate parameter. Interaction between the parameters resulted in large variations in treatment effect estimates. Effect estimates calculated from model outputs showed a quadratic curve with a clear optimum at low, but not the lowest, transmission rates. These results indicated that overall positive population level effects of lactation therapy would be realized for herds that have successfully implemented practices that reduce the transmission rate of pathogens. A key finding is that in herds with high transmission rates, treatment of chronically infected quarters was predicted to have little impact on the proportion of infected quarters and no positive population level effect in reducing the force of infection and new infection rates. Results of this study suggest that field trials to evaluate efficacy of antimicrobial treatment should include estimates of indirect treatment effects. (C) 2009 Elsevier B.V. All rights reserved.

Item Type:	Journal Article
Subjects:	S Agriculture > SF Animal culture
Divisions:	Faculty of Science > Life Sciences (2010- ) > Biological Sciences ( -2010)
Journal or Publication Title:	Preventive Veterinary Medicine
Publisher:	Elsevier
ISSN:	0167-5877
Date:	1 July 2009
Volume:	Vol.90
Number:	No.1-2
Number of Pages:	12
Page Range:	pp. 31-42
Identification Number:	10.1016/j.prevetmed.2009.03.016
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access
Funder:	USDA, USDA-CSREES
Grant number:	2005-35204-15651, VT-AH01011
URI:	http://wrap.warwick.ac.uk/id/eprint/27772

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