Designing a risk-based surveillance program for Mycobacterium avium ssp. paratuberculosis in Norwegian dairy herds using multivariate statistical process control analysis.

Surveillance programs for animal diseases are critical to early disease detection and risk estimation and to documenting a population's disease status at a given time. The aim of this study was to describe a risk-based surveillance program for detecting Mycobacterium avium ssp. paratuberculosis (MAP) infection in Norwegian dairy cattle. The included risk factors for detecting MAP were purchase of cattle, combined cattle and goat farming, and location of the cattle farm in counties containing goats with MAP. The risk indicators included production data [culling of animals >3 yr of age, carcass conformation of animals >3 yr of age, milk production decrease in older lactating cows (lactations 3, 4, and 5)], and clinical data (diarrhea, enteritis, or both, in animals >3 yr of age). Except for combined cattle and goat farming and cattle farm location, all data were collected at the cow level and summarized at the herd level. Predefined risk factors and risk indicators were extracted from different national databases and combined in a multivariate statistical process control to obtain a risk assessment for each herd. The ordinary Hotelling's T(2) statistic was applied as a multivariate, standardized measure of difference between the current observed state and the average state of the risk factors for a given herd. To make the analysis more robust and adapt it to the slowly developing nature of MAP, monthly risk calculations were based on data accumulated during a 24-mo period. Monitoring of these variables was performed to identify outliers that may indicate deviance in one or more of the underlying processes. The highest-ranked herds were scattered all over Norway and clustered in high-density dairy cattle farm areas. The resulting rankings of herds are being used in the national surveillance program for MAP in 2014 to increase the sensitivity of the ongoing surveillance program in which 5 fecal samples for bacteriological examination are collected from 25 dairy herds. The use of multivariate statistical process control for selection of herds will be beneficial when a diagnostic test suitable for mass screening is available and validated on the Norwegian cattle population, thus making it possible to increase the number of sampled herds.

Prediction of clinical mastitis outcomes within and between environments using whole-genome markers.

The objective of this study was to evaluate genome-enabled predictions of daughter yield deviations for clinical mastitis in Norwegian Red cows within and between environments according to mastitis pathogen status. Genome-based predictions of daughter yield deviations for clinical mastitis for 1,126 bulls within and between 5 environments were performed using Bayesian ridge regression. The environments were defined as herd-5-yr classes with the following prevalence of bacteriological milk samples found positive for contagious mastitis pathogens: <50% (L50), ≥ 50% (H50), ≤ 25% (L75), >25% and <75% (M75), and ≥ 75% (H75). In addition, predictions based on all data across environment groups (the full data set, FD) were calculated to provide a benchmark for comparison. Predictive ability was evaluated using a 10-fold cross validation. A bootstrap procedure was used to obtain 95% confidence intervals for the cross-validation distribution of predictive ability for each data set. Predictive ability ranged from 0.04 for L75 to 0.19 for FD. Similar predictions within and between environments showed no evidence of genotype by environment interaction. The 95% confidence interval for all 5 environmental data sets included zero and ranged from 0.02 to 0.35 for FD. The bootstrap distribution showed large variation within each data set and small variation between data sets. Although we found no evidence of genotype by environment interaction, rank correlations of the single nucleotide polymorphism effects between different environments ranged from 0.15 (L75 - H75) to 0.92 (M75 - FD), indicating that single nucleotide polymorphisms may have a differential contribution to predictive ability in environments with distinct pathogen loads.

Genetic associations between somatic cell score and pathogen-specific subclinical mastitis in Norwegian Red cows.

The aim of this study was to estimate heritabilities of and genetic correlations between pathogen-specific subclinical mastitis (SCM) traits and lactation mean somatic cell score (LSCS) in Norwegian Red cattle. Based on data from 130 733 first-lactation cows four binary pathogen-specific SCM traits, Staphylococcus aureus, Streptococcus dysgalactiae, Streptococcus uberis and coagulase-negative staphylococci SCM, were analysed together with unspecific SCM and LSCS using a multivariate sire model with threshold models for binary traits and a linear model for LSCS. Posterior means (SD) of heritabilities were 0.17 (0.01) for LSCS, 0.11 (0.01) for liability to unspecific SCM and ranged from 0.04 (Staph. aureus) to 0.14 (Strep. dysgalactiae) for liability to pathogen-specific SCM. Genetic correlations were positive and moderate to high, ranging from 0.37 to 0.98. All genetic correlations except the one between LSCS and unspecific SCM were lower than 1, indicating that SCM caused by different pathogens can be considered as partly different traits.

Genetic analysis of pathogen-specific clinical mastitis in Norwegian Red cows.

The objective of this study was to estimate heritabilities and genetic correlations for pathogen-specific clinical mastitis (CM) in Norwegian Red cows. In Norway, breeding values for mastitis are predicted based on records of veterinary treatments of clinical mastitis. Bacteriological milk sample results from the mastitis laboratories have been recorded routinely into the Norwegian Dairy Herd Recording System since 2000, but have so far not been used in genetic analyses. This additional source of data may provide valuable information on pathogen-specific CM. Records from 234,088 first-lactation Norwegian Red cows, daughters of 1,656 sires, were used for genetic analyses of unspecific, Staphylococcus aureus, Streptococcus dysgalactiae, and Escherichia coli CM. The 4 CM traits were defined as binary and scored as 1 if the cow had at least 1 case of the CM in question and 0 otherwise. A Bayesian approach using Gibbs sampling was applied, and a multivariate threshold liability model was used for the analyses. The posterior mean (SD ≤ 0.01) of the heritabilities were 0.06 for liability of unspecific CM, 0.04 for Staph. aureus CM, 0.02 for Strep. dysgalactiae CM, and 0.03 for E. coli CM. The posterior mean (SD) of the genetic correlations were all high, ranging from 0.75 (0.14) to 0.87 (0.07). The highest genetic correlation was found between unspecific CM and Strep. dysgalactiae CM, whereas the lowest was found for E. coli CM and Staph. aureus CM. Genetic correlations lower than 1 indicate that mastitis caused by different pathogens can be considered as partly different traits. In spite of high rank correlations (0.95-0.98), some re-ranking of sires was observed.

Meta-analysis of dry cow management for dairy cattle. Part 2. Cure of existing intramammary infections.

The main goal of dry cow therapy (DCT) is to cure existing intramammary infections (IMI) at dry off. Although several published studies have estimated the cure rate of IMI after DCT, variation among studies is great, which makes it difficult to conduct a proper economic evaluation of DCT. The objective of the present meta-analysis of existing peer-reviewed literature was to provide a summary quantification of quarter IMI cure based on DCT. A meta-analysis relative risk (RR) was calculated per intervention and pathogen group when at least 4 studies were available for analysis per comparison from the 22 selected studies, according to the selection criteria. Results of the meta-analysis were examined using publication bias tests. Blanket DCT with a 95% confidence interval (CI) provided a 1.78 (1.51 to 2.10) times higher calculated cure rate from quarter IMI during the dry period up to 21 d postcalving, compared with no DCT. The RR of cure was similar when treatment was conducted for Streptococcus spp. IMI quarters compared with Staphylococcus spp. IMI quarters. The pooled RR with the 95% CI were 1.83 (1.48 to 2.35) and 1.65 (1.38 to 1.96), respectively. There was no significant difference between cloxacillin and other DCT products in the cure of quarter IMI during the dry period up to 21 d postcalving. The pooled RR with the 95% CI was 1.00 (0.92 to 1.09). Similarly, there was no significant difference between cloxacillin and other DCT products in the cure of quarter Staphylococcus spp. IMI. The pooled RR with the 95% CI was 1.00 (0.96 to 1.06). The pooled RR with the 95% CI of quarter IMI cure using selective DCT, compared with no DCT, was 1.76 (1.23 to 2.54).

Streptococcus dysgalactiae isolates at calving and lactation performance within the same lactation.

The objective of the study was to investigate the association between early lactation Streptococcus dysgalactiae isolates and milk yield, somatic cell count (SCC), clinical mastitis, and culling in the same lactation. The 178 commercial dairy herds were randomly placed into 3 penicillin- or penicillin-dihydrostreptomycin-based dry-cow treatments and 3 different postmilking teat disinfection groups-negative control, iodine, or external teat sealant. All cows were sampled in early lactation, and Strep. dysgalactiae-positive and culture-negative cows were followed throughout the remainder of the lactation. Mixed models, including repeated measurements, with test-day observation as dependent variable, were used to compare milk yield, SCC, and available milk quality variables throughout the remaining lactation. Survival analyses, using a positive frailty model to account for any herd random effects, were used to estimate the hazard ratio for clinical mastitis and culling. Streptococcus dysgalactiae-positive cows had a significantly higher SCC throughout the lactation compared to culture-negative cows. For primiparous or multiparous cows, respectively, the differences in the geometric mean SCC between Strep. dysgalactiae-positive and culture-negative cows was 197,000 or 280,000 cells/mL at the beginning of the lactation, 24,000 or 46,000 cells/mL in mid lactation, and 39,000 or 111,000 cells/mL at the end of the lactation. Streptococcus dysgalactiae-positive primiparous or multiparous cows produced 334 or 246 kg less milk, respectively, during a 305-d lactation compared with culture-negative cows. Compared with culture-negative cows, the hazard ratios for clinical mastitis in Strep. dysgalactiae-positive cows were 2.3 (1.9 to 2.9) and 1.6 (1.3 to 2.0) for culling. For cows with both Strep. dysgalactiae and Staphylococcus aureus isolates, the hazard ratio for culling significantly increased to 2.5 (1.9 to 3.2).

Clinical mastitis in Norwegian herds after a combined selective dry-cow therapy and teat-dipping trial.

The objective of this study was to see if introduction of a 2-yr combined selective dry-cow therapy and teat-dipping trial would reduce clinical mastitis (CM) events in 164 Norwegian dairy herds. Three different penicillin or penicillin/dihydrostreptomycin-based dry-cow treatments, and 3 different teat-dipping regimens (negative control, iodine teat dip, or an external teat sealant) were independently and randomly allocated to each herd. Complete lactations both before and during the trial were investigated. Altogether, 1,005 CM cases were recorded in the lactations before the trial and 924 cases were recorded during the trial. Bacteriological milk samples were available from 784 of the 924 CM cases during the trial. Among these, Staphylococcus aureus were isolated from 47.4%, Streptococcus dysgalactiae from 22.5%, Escherichia coli from 10.7%, and coagulase-negative staphylococci from 6.3%. In addition, 12.5% cases were bacteriological negative, and the remainder of the CM cases were caused by other microbes. The different models were analyzed using Cox regression analysis with PROC PHREG and a positive stable frailty model in the SAS macro. Separate models were made for cows housed in tie-stalls and free-stalls. Parity had a significant impact on the CM risk in both type of stalls. Older cows (parity > 3) had the highest hazard ratio of contracting CM in tie-stalls (1.68) and free-stalls (2.18) compared with parity 1. The CM risk decreased significantly (13%) in tie-stalls and by 18% in free-stalls. In tie-stalls, iodine-dipped cows had a significantly lower chance (21%) of getting CM compared with the negative control and the use of external teat sealant. The same trend was seen in free-stalls; however, the differences were not significant. Compared with CM before the trial, the reduction of CM was 15% during the trial.