Partial prediction of the duration and the clinical status of Staphylococcus aureus bovine intramammary infections based on the phenotypic and genotypic analysis of isolates

S Pichette-Jolette, G Millette, E Demontier, D Bran-Barrera, M Cyrenne, C Ster, D Haine, G Keefe, F Malouin, JP Roy

Staphylococcus aureus is a bacterial pathogen causing bovine intramammary infections (IMIs) often leading to chronic clinical or subclinical mastitis. Predicting the outcome of S. aureus IMIs (duration and clinical vs subclinical) based on the characterization of isolates would help to make better case management decisions. For this purpose, 583 S. aureus isolates from series of quarter milk samples were characterized by genotypic tests (detection of virulence genes seg, tst, lukM), epidemiological typing (spa type) and by a phenotypic test (biofilm production). Read More

Selection and misclassification biases in longitudinal studies

D Haine, I Dohoo, S Dufour

Using imperfect tests may lead to biased estimates of disease frequency and measures of association. Many studies have looked into the effect of misclassification on statistical inferences. These evaluations were either within a cross-sectional study framework, assessing biased prevalence, or for cohort study designs, evaluating biased incidence rate or risk ratio estimates based on misclassification at one of the two time-points (initial assessment or follow-up). However, both observations at risk and incident cases can be wrongly identified in longitudinal studies, leading to selection and misclassification biases, respectively. Read More

Herd-level mastitis-associated costs on Canadian dairy farms

M Aghamohammadi, D Haine, DF Kelton, HW Barkema, H Hogeveen, GP Keefe, S Dufour

Mastitis imposes considerable and recurring economic losses on the dairy industry worldwide. The main objective of this study was to estimate herd-level costs incurred by expenditures and production losses associated with mastitis on Canadian dairy farms in 2015, based on producer reports. Previously, published mastitis economic frameworks were used to develop an economic model with the most important cost components. Components investigated were divided between clinical mastitis (CM), subclinical mastitis (SCM), and other costs components (i. Read More

Early-lactation extended pirlimycin therapy against naturally acquired Staphylococcus aureus intramammary infections in heifers: A randomized controlled trial

S Skoulikas, S Dufour, D Haine, J-Y Perreault, J-P Roy

The primary objective of the current study was to evaluate cure rate following an early-lactation extended intramammary pirlimycin treatment on heifers naturally infected by Staphylococcus aureus. The secondary objective was to assess Petrifilm Staph Express (3M Microbiology, St. Paul, MN) count plate characteristics when used in a protocol for early-lactation detection of infected quarters in heifers. Milk samples were collected from heifers (n = 946) in the first few days following calving (mean = 5 d). Read More

Diagnosing intramammary infection: Controlling misclassification bias in longitudinal udder health studies

D Haine, I Dohoo, D Scholl, S Dufour

Using imperfect tests may lead to biased estimates of disease frequency and of associations between risk factors and disease. For instance in longitudinal udder health studies, both quarters at risk and incident intramammary infections (IMI) can be wrongly identified, resulting in selection and misclassification bias, respectively. Diagnostic accuracy can possibly be improved by using duplicate or triplicate samples for identifying quarters at risk and, subsequently, incident IMI. The objectives of this study were to evaluate the relative impact of selection and misclassification biases resulting from IMI misclassification on measures of disease frequency (incidence) and of association with hypothetical exposures. Read More

Culling from the actors' perspectives—Decision-making criteria for culling in Québec dairy herds enrolled in a veterinary preventive medicine program

D Haine, H Delgado, R Cue, A Sewalem, K Wade, R Lacroix, D Lefebvre, J Rushton, J Arsenault, É Bouchard, J Dubuc

The series of events leading to the decision to cull a cow is complex, involving both individual-level and herd-level factors. While the decision is guided by financial returns, it is also influenced by social and psychological factors. Research studies on the motivational and behavioural aspects of farmers’ decision utility are sparse, and nonexistent regarding culling expectations and its decision process. Our goal was to identify shared criteria on culling decisions held by dairy producers and farm advisers, with the help of the Q-methodology. Read More

Culling from the herd's perspective—Exploring herd-level management factors and culling rates in Québec dairy herds

D Haine, H Delgado, R Cue, A Sewalem, K Wade, R Lacroix, D Lefebvre, J Arsenault, É Bouchard, J Dubuc

The relationship between cows’ health, reproductive performance or disorders and their longevity is well demonstrated in the literature. However these associations at the cow level might not hold true at the herd level, and herd-level variables can modify cow-level outcomes independently of the cows’ characteristics. The interaction between cow-level and herd-level variables is a relevant issue for understanding the culling of dairy cows. However it requires the appropriate group-level variables to assess any contextual effect. Read More

Marginal structural Cox model to estimate the causal effect of clinical mastitis on Québec dairy cow culling risk

D Haine, H Delgado, R Cue, A Sewalem, K Wade, R Lacroix, D Lefebvre, J Arsenault, É Bouchard, J Dubuc

Health disorders, such as milk fever, displaced abomasum, or retained placenta, as well as poor reproductive performance, are known risk factors for culling in dairy cows. Clinical mastitis (CM) is one of the most influential culling risk factors. However the culling decision could be based either on the disease status or on the current milk yield, milk production being a significant confounder when modelling dairy cow culling risk. But milk yield (and somatic cell count) are time-varying confounders, which are also affected by prior CM and therefore lie on the causal pathway between the exposure of interest, CM, and the outcome, culling. Read More

Contextual herd factors associated with cow culling risk in Québec dairy herds: A multilevel analysis

D Haine, H Delgado, R Cue, A Sewalem, K Wade, R Lacroix, D Lefebvre, J Arsenault, É Bouchard, J Dubuc

Several health disorders, such as milk fever, displaced abomasum, and mastitis, as well as impaired reproductive performance, are known risk factors for the removal of affected cows from a dairy herd. While cow-level risk factors are well documented in the literature, herd-level associations have been less frequently investigated. The objective of this study was to investigate the effect of cow- and herd-level determinants on variations in culling risk in Québec dairy herds: whether herd influences a cow’s culling risk. Read More

Prediction of bulk tank somatic cell count violations based on monthly individual cow somatic cell count data

V Fauteux, É Bouchard, D Haine, DT Scholl, J-P Roy

The regulatory limit in Canada for bulk tank somatic cell count (BTSCC) was recently lowered from 500,000 to 400,000 cells/mL. Herd indices based on changes in cow somatic cell count over 2 consecutive months (e.g., proportion of healthy or chronically infected cows, cows cured, and new intramammary infection rate) could be used as predictors for BTSCC violations. The objective of this study was to develop a predictive model for exceeding the limit of 400,000 cells/mL in the next month using these herd indices. Read More