TY - JOUR
T1 - Effect of carryover and presampling procedures on the results of real-time PCR used for diagnosis of bovine intramammary infections with Streptococcus agalactiae at routine milk recordings
AU - Mahmmod, Yasser
AU - Mweu, Marshal Mutinda
AU - Nielsen, Søren Saxmose
AU - Katholm, Jørgen
AU - Klaas, Ilka Christine
PY - 2014/3/1
Y1 - 2014/3/1
N2 - The use of PCR tests as diagnostics for intramammary infections (IMI) based on composite milk samples collected in a non-sterile manner at milk recordings is increasing. Carryover of sample material between cows and non-aseptic PCR sampling may be incriminated for misclassification of IMI with Streptococcus agalactiae (S. agalactiae) in dairy herds with conventional milking parlours. Misclassification may result in unnecessary costs for treatment and culling. The objectives of this study were to (1) determine the effect of carryover on PCR-positivity for S. agalactiae at different PCR cycle threshold (Ct) cut-offs by estimating the between-cow correlation while accounting for the milking order, and (2) evaluate the effect of aseptic presampling procedures (PSP) on PCR-positivity at the different Ct-value cut-offs. The study was conducted in four herds with conventional milking parlours at routine milk recordings. Following the farmers' routine pre-milking preparation, 411 of 794 cows were randomly selected for the PSP treatment. These procedures included removing the first streams of milk and 70% alcohol teat disinfection. Composite milk samples were then collected from all cows and tested using PCR. Data on milking order were used to estimate the correlation between consecutively milked cows in each milking unit. Factors associated with the PCR-positivity for S. agalactiae were analyzed using generalized estimating equations assuming a binomially-distributed outcome with a logit link function. Presampling procedures were only significant using cut-off 37. A first-order autoregressive correlation structure provided the best correlation between consecutively milked cows. The correlation was 13%, 11%, 9% at cut-offs
AB - The use of PCR tests as diagnostics for intramammary infections (IMI) based on composite milk samples collected in a non-sterile manner at milk recordings is increasing. Carryover of sample material between cows and non-aseptic PCR sampling may be incriminated for misclassification of IMI with Streptococcus agalactiae (S. agalactiae) in dairy herds with conventional milking parlours. Misclassification may result in unnecessary costs for treatment and culling. The objectives of this study were to (1) determine the effect of carryover on PCR-positivity for S. agalactiae at different PCR cycle threshold (Ct) cut-offs by estimating the between-cow correlation while accounting for the milking order, and (2) evaluate the effect of aseptic presampling procedures (PSP) on PCR-positivity at the different Ct-value cut-offs. The study was conducted in four herds with conventional milking parlours at routine milk recordings. Following the farmers' routine pre-milking preparation, 411 of 794 cows were randomly selected for the PSP treatment. These procedures included removing the first streams of milk and 70% alcohol teat disinfection. Composite milk samples were then collected from all cows and tested using PCR. Data on milking order were used to estimate the correlation between consecutively milked cows in each milking unit. Factors associated with the PCR-positivity for S. agalactiae were analyzed using generalized estimating equations assuming a binomially-distributed outcome with a logit link function. Presampling procedures were only significant using cut-off 37. A first-order autoregressive correlation structure provided the best correlation between consecutively milked cows. The correlation was 13%, 11%, 9% at cut-offs
UR - http://www.scopus.com/inward/record.url?scp=84892727311&partnerID=8YFLogxK
U2 - 10.1016/j.prevetmed.2014.01.002
DO - 10.1016/j.prevetmed.2014.01.002
M3 - Journal article
C2 - 24467998
SN - 0167-5877
VL - 113
SP - 512
EP - 521
JO - Preventive Veterinary Medicine
JF - Preventive Veterinary Medicine
IS - 4
ER -