Temporal patterns of bovine leukemia virus infection in dairy herds in Atlantic Canada.

Objective: The primary objective was to determine the youngest age group where bovine leukemia virus (BLV)-infected dairy animals were identified. The secondary objective was to investigate associations between age-specific management practices and BLV infection status of different age groups of dairy calves and heifers. Procedure: For enrolled herds, BLV status was determined using blood samples from pre-weaned calves, weaned calves, and breeding-age heifers; and bulk tank milk from the adult herd. A questionnaire investigating age-specific management factors was administered for each herd. Ordinal logistic regression was performed to identify management factors associated with the youngest age range in which BLV was identified. Results: Fifty-three dairy herds from the 4 provinces in Atlantic Canada were enrolled. Bovine leukemia virus was most commonly earliest identified in pre-weaned heifers (18 herds, 32.1%) and the adult herd (18 herds, 32.1%). Ordinal logistic regression revealed that BLV was first identified in older age groups more often than in younger age groups when herds regrouped weaned heifers at least once, when fly control was used for breeding-age heifers, when herds practiced foot trimming on breeding-age heifers, and when bred heifers were brought in. Conclusion: Producers can use results to identify the youngest age group(s) in which BLV is identified and to tailor management strategies to prevent new infections.

Tendances temporelles de l'infection par le virus de la leucémie bovine dans les troupeaux laitiers des provinces atlantiques canadiennes. Objectif: L'objectif principal était de déterminer le groupe d'âge le plus jeune dans lequel les animaux laitiers infectés par le virus de la leucémie bovine (BLV) ont été identifiés. L'objectif secondaire était d'étudier les associations entre les pratiques de gestion spécifiques à l'âge et le statut d'infection par le BLV de différents groupes d'âge de veaux et de génisses laitiers. Procédure: Pour les troupeaux inscrits, le statut BLV a été déterminé à l'aide d'échantillons de sang provenant de veaux présevrés, de veaux sevrés et de génisses en âge de se reproduire; et de lait de réservoir en vrac du troupeau adulte. Un questionnaire portant sur les facteurs de gestion spécifiques à l'âge a été administré pour chaque troupeau. Une régression logistique ordinale a été réalisée pour identifier les facteurs de gestion associés à la tranche d'âge la plus jeune dans laquelle le BLV a été identifié. Résultats: Cinquante-trois troupeaux laitiers des quatre provinces atlantiques canadiennes ont été inscrits. Le virus de la leucémie bovine a été le plus souvent identifié le plus tôt chez les génisses pré-sevrées (18 troupeaux, 32,1 %) et dans le troupeau adulte (18 troupeaux, 32,1 %). La régression logistique ordinale a révélé que le BLV a été identifié pour la première fois plus souvent dans les groupes d'âge plus âgés que dans les groupes d'âge plus jeunes lorsque les troupeaux regroupaient au moins une fois les génisses sevrées, lorsque le contrôle des mouches était utilisé pour les génisses en âge de se reproduire, lorsque les troupeaux pratiquaient le parage des pattes des génisses en âge de se reproduire., et quand les taures saillies étaient intégrées au troupeau. Conclusion: Les producteurs peuvent utiliser les résultats pour identifier le(s) groupe(s) d'âge le plus jeune dans lequel le BLV est identifié et pour adapter les stratégies de gestion afin de prévenir de nouvelles infections.(Traduit par Dr Serge Messier).

Diagnosing Intramammary Infection: Meta-Analysis and Mapping Review on Frequency and Udder Health Relevance of Microorganism Species Isolated from Bovine Milk Samples.

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry provides accurate species-level identification of many, microorganisms retrieved from bovine milk samples. However, not all those microorganisms are pathogenic. Our study aimed to: (1) determine the species-specific prevalence of microorganisms identified in bovine milk of apparently healthy lactating quarters vs. quarters with clinical mastitis (CM); and (2) map current information and knowledge gaps on udder health relevance of microorganisms retrieved from bovine milk samples. A mixed study design (meta-analysis and mapping review) was chosen. We gathered several large Canadian, US and Brazilian data sets of MALDI-TOF results for organisms cultured from quarter milk samples. For meta-analysis, two datasets (apparently healthy quarters vs. CM samples) were organized. A series of meta-analyses was conducted to determine microorganisms' prevalence. Then, each species reported was searched through PubMed to investigate whether inflammation (increased somatic cell count (SCC) or signs of CM) was associated with microorganism's recovery from milk. A total of 294 different species of microorganisms recovered from milk samples were identified. Among 50,429 quarter-milk samples from apparently healthy quarters, the 5 most frequent species were Staphylococcus chromogenes (6.7%, 95% CI 4.5-9.2%), Aerococcus viridans (1.6%, 95% CI 0.4-3.5%), Staphylococcus aureus (1.5%, 95% CI 0.5-2.8%), Staphylococcus haemolyticus (0.9%, 95% CI 0.4-1.5%), and Staphylococcus epidermidis (0.7%, 95% CI 0.2-1.6%). Among the 43,924 quarter-milk CM samples, the 5 most frequent species were Escherichia coli (11%, 95% CI 8.1-14.3%), Streptococcus uberis (8.5%, 95% CI 5.3-12.2%), Streptococcus dysgalactiae (7.8%, 95% CI 4.9-11.5%), Staphylococcus aureus (7.8%, 95% CI 4.4-11.9%), and Klebsiella pneumoniae (5.6%, 95% CI 3.4-8.2%). When conducting the PubMed literature search, there were 206 species identified by MALDI-TOF for which we were not able to find any information regarding their association with CM or SCC. Some of them, however, were frequently isolated in our multi-country dataset from the milk of quarters with CM (e.g., Citrobacter koseri, Enterococcus saccharolyticus, Streptococcus gallolyticus). Our study provides guidance to veterinarians for interpretation of milk bacteriology results obtained using MALDI-TOF and identifies knowledge gaps for future research.

Development of a predictive model for bovine leukemia virus proviral load.

BACKGROUND: There is currently no commercially available method in Canada to identify bovine leukemia virus (BLV)-positive cows with high proviral load (PVL). OBJECTIVES: First, develop a model to predict PVL using common, commercially available, cost-effective diagnostic tests. Second, investigate the relationship between lymphocyte count and PVL in BLV-positive cows. ANIMALS: A total of 339 BLV-positive and 62 BLV-seronegative cows on 15 dairy farms. METHODS: Cross-sectional study. Blood and milk samples were collected from all lactating BLV-positive cows on each farm and 5 to 10 BLV-seronegative cows depending on herd size. Blood and milk samples were tested for anti-BLV antibodies using enzyme-linked immunosorbent assay (ELISA). Complete blood counts were performed on blood samples, and standard components analyses were obtained for milk samples. Proviral load was determined by quantitative polymerase chain reaction for each cow. RESULTS: The inverse of lymphocyte count, the square of the inverse of lymphocyte count, and milk ELISA percent positivity were positively associated with increasing PVL in BLV-positive cows. For BLV-positive cows, lymphocyte count >5.2 × 109 /L predicted a high PVL (BLV:Bovine DNA of >1 in blood) with a sensitivity of 92.4% and a specificity of 79.8%. For BLV-positive cows, white blood cell count >10.8 × 109 /L predicted a high PVL, with a sensitivity of 85.5% and a specificity of 83.6%. CONCLUSIONS AND CLINICAL IMPORTANCE: Based on these results, producers can implement commonly available diagnostic tests to identify cows with high probability of having high PVL, which may help in designing effective disease control strategies for BLV-positive herds.

Communication skills training and assessment of food animal production medicine veterinarians: A component of a voluntary Johne's disease control program.

In food animal production medicine (FAPM), the success of control programs for infectious diseases that have serious animal health and economic consequences frequently rely on the veterinarian's effective communication and producer adherence to veterinary recommendations. However, little research has been conducted on communication skills of practicing FAPM veterinarians. During this study, we developed a communication training workshop intervention to support the Atlantic Johne's Disease Initiative. Seventeen FAPM veterinarians across 10 clinics practicing within Maritime Canada participated in a pre-post intervention study design. Communication skills were evaluated utilizing 3 assessment tools; an objective structured clinical exam (OSCE), standardized client feedback, and an instrument designed for veterinary participants to assess their self-efficacy. Study results showed that before training, communication skills of participating veterinarians had limitations, including skill deficits in communication tasks strongly associated with increased adherence to veterinary recommendations. Based on the 3 assessment tools, communication skills of participating veterinarians improved with the training provided. Significant increases were detected in pre- to postintervention self-efficacy percentage scores, OSCE percentage and global scores from expert raters, and OSCE percentage and global scores from standardized client feedback. These improvements emphasize the importance of communication skills training specific to FAPM.

Dairy producer satisfaction and knowledge transfer with the veterinary-administered risk assessment and management plan in a voluntary Johne's disease control program.

The Atlantic Johne's Disease Initiative (AJDI) aims to control Mycobacterium avium ssp. paratuberculosis infection by using veterinary-administered risk assessments to identify high-risk management practices and prompt changes in management behavior. Objectives for this study were to measure producer satisfaction with the veterinary-administered risk assessment and management plan (RAMP) process in a voluntary Johne's disease (JD) control program, compare RAMP-specific satisfaction results based on herd JD status, and measure knowledge transfer from certified veterinarians to producers during the RAMP. A satisfaction questionnaire was adapted to the RAMP process in the AJDI to measure producer satisfaction. The questionnaire included 9 RAMP-specific producer satisfaction items, 1 global RAMP satisfaction item, and 16 questions to assess producer knowledge and knowledge translation about JD, bovine viral diarrhea (BVD), and bovine leukosis virus (BLV) during the RAMP (BVD and BLV used for comparison purposes). A total of 133 dairy producers in the AJDI (79.6% response rate) completed the questionnaire by telephone. The RAMP-specific satisfaction was high among the AJDI producers surveyed, and these results were not found to differ based on herd JD status. The lowest satisfaction scores and the highest number of "unable to assess" responses were for the item relating to cost. Factors that contributed to RAMP-specific producer satisfaction were not identified from the demographic and herd information available in this study. The knowledge scores indicated moderate knowledge about JD and fair knowledge about BVD and BLV. Evidence of knowledge translation from the RAMP was mixed in this study. Bovine viral diarrhea knowledge scores were not found to differ based on whether or not the certified veterinarian discussed BVD during the preceding RAMP, but BLV knowledge scores were higher among dairy producers that discussed BLV during the preceding RAMP. Strengths and gaps in producer knowledge about these 3 infectious diseases were identified. By using this producer questionnaire, interventions aimed at improving the content, delivery, and satisfaction of RAMP in JD control programs, such as the AJDI, can be developed.

Bayesian estimation of diagnostic accuracy of somatic cell counts history and on-farm milk culture using Petrifilm® to identify quarters or cows that should be treated with antimicrobials in selective treatment protocols at dry off.

Bayesian latent class models were used to estimate the test accuracy (sensitivity (Se), specificity (Sp), and predictive values (NPV and PPV)) of cow-level somatic cell counts (SCC) data, quarter-level Petrifilm® on-farm milk culture, and quarter-level standard milk bacteriology for the identification of quarters that should possibly be treated with antimicrobials at dry off in dairy cows. Data of 282 cows from 9 dairy herds in Québec, Canada, with bulk tank SCC < 250,000 cells/mL were used. Estimated median herd-prevalence of infections that should be treated was 16.2 % (95 % credibility interval (CI): 11.0-22.7). Se and Sp estimates for quarter-milk culture using Petrifilm® were 82.2 % (95 %CI: 74.0-89.5) and 62.0 % (95 %CI: 58.6-65.6), respectively. Se and Sp for quarter-milk standard bacteriology were 67.4 % (95 %CI: 55.8-81.2) and 79.6 % (95 %CI: 76.4-83.0), respectively. Se and Sp of different SCC scenarios and thresholds were estimated. For first parity cows, using only the last Dairy Herd Improvement (DHI) test SCC with a threshold of 100,000 cells/mL appeared quite accurate, with Se, Sp, PPV, NPV and reduction of antimicrobial usage of 85.6 % (95 %CI: 69.6-95.6), 86.0 % (95 %CI: 80.0-91.7), 58.0 % (95 %CI: 42.3-74.2), 96.4 % (95 %CI: 91.3-99.0), and 75.3 % (95 %CI: 70.7-79.3), respectively. For cows of ≥ 2nd parity, using only the last DHI test SCC with a threshold of 200,000 cells/mL resulted in Se, Sp, PPV, NPV and reduction of antimicrobial usage of 75.3 % (95 %CI: 55.8-87.3), 84.0 % (95 %CI: 78.8-89.3), 47.2 % (95 %CI: 32.0-63.7), 94.7 % (95 %CI: 89.0-97.6), and of 77.0 % (95 %CI: 73.3-80.3), respectively. Adding quarter-level milk culture using Petrifilm® to cows identified as unhealthy using cow-level SCC data improved the test accuracy (mainly the PPV) and further reduced the use of antimicrobials. For instance, in ≥ 2nd parity cows, using only the last DHI SCC with a threshold of 200,000 cells/mL, adding a subsequent Petrifilm® test increased the reduction from 77.0 % (95 %CI: 73.3-80.3) to 89.5 % (95 %CI: 86.7-91.8). Considering the availability of SCC data, the easiness of using just the last DHI test, and the high NPV that could be achieved, producers may consider using just the last DHI test as a potential tool to identify cows that should be treated with antimicrobials at dry off. It may be used alone or in combination with quarter-level on-farm Petrifilm® milk culture on high SCC cows to further reduce the use of antimicrobials by identifying quarters that need to be treated.

Evaluation of quarter-based selective dry cow therapy using Petrifilm on-farm milk culture: A randomized controlled trial.

The objective of this randomized controlled trial was to assess the efficacy of an on-farm culture system using Petrifilm (3M, London, ON, Canada) for targeted treatment decisions at the quarter level at dry-off and its effects on dry period intramammary infections (IMI) and udder health and milk production in the subsequent lactation. A total of 568 cows (2,247 quarters) from 9 dairy herds with bulk tank somatic cell count <250,000 cells/mL in Québec, Canada, were systematically enrolled and randomly allocated to 4 groups: 2 quarter-based selective (QSDCT) groups, using results of quarter-milk culture on Petrifilm, and 2 blanket dry cow therapy (BDCT) groups. The 2 QSDCT groups consisted of (1) antimicrobial to infected quarters and internal teat sealant (ITS) to healthy quarters (QSDCT/ITS); and (2) antimicrobial and ITS to infected quarters and ITS to healthy quarters (QSDCT+ITS/ITS). The 2 BDCT groups were (1) antimicrobial alone to all quarters (BDCT); and (2) antimicrobial and ITS to all quarters (BDCT+ITS). Quarter milk samples were collected at dry-off and after calving for routine bacteriological culture at the laboratory to monitor IMI; data on milk production, somatic cell count, and clinical mastitis recorded up to 120 d in milk were retrieved from health and DHI records. The probability of avoiding antimicrobial treatment in QSDCT groups was estimated at 48.3% (95% confidence interval: 35.7, 60.9). There was no significant difference between the 4 treatment groups regarding acquisition of new IMI (15.9, 13.2, 15.8, and 15.1% probability for BDCT, BDCT+ITS, QSDCT/ITS, and QSDCT+ITS/ITS, respectively) or persistence of existing IMI (3.2, 2.1, 3.4, and 2.7% probability, respectively) over the dry period. In the subsequent lactation, there was no difference between groups regarding incidence of clinical mastitis (2.4, 3.7, 2.9, and 1.7% respectively for BDCT, BDCT+ITS, QSDCT/ITS, and QSDCT+ITS/ITS), mean milk somatic cell score (1.7, 2.0, 2.0, and 2.0 respectively), or mean daily milk production (43.8, 44.2, 43.2, and 42.6 kg/d, respectively) during the first 120 d in milk. In conclusion, QSDCT using the Petrifilm on-farm culture system to detect infected quarters at dry-off is an interesting option to decrease antibiotic use without any negative effects on udder health or milk production in the first 120 d of the subsequent lactation compared with BDCT.

Short communication: Whole-genome sequence analysis of 4 fecal blaCMY-2-producing Escherichia coli isolates from Holstein dairy calves.

This study was carried out to determine the antimicrobial resistance (AMR) genes and mobile genetic elements of 4 fecal blaCMY-2-producing Escherichia coli isolated from Holstein dairy calves on the same farm using whole-genome sequencing. Genomic analysis revealed that 3 of the 4 isolates shared similar genetic features, including sequence type (ST), serotype, plasmid characteristics, insertion ST, and virulence genes. In addition to genes encoding for complex multidrug resistance efflux systems, all 4 isolates were carriers of genes conferring resistance to ß-lactams (blaCMY-2, blaTEM-1B), tetracyclines (tetA, tetB, tetD), aminoglycosides [aadA1, aph(3")-lb, aph(6)-ld], sulfonamides (sul2), and trimethoprim (dfrA1). We also detected 4 incompatibility plasmid groups: Inc.F, Inc.N, Inc.I, and Inc.Q. A novel ST showing a new purA and mdh allelic combination was found. The 4 isolates were likely enterotoxigenic pathotypes of E. coli, based on serotype and presence of the plasmid Inc.FII(pCoo). This study provides information for comparative genomic analysis of AMR genes and mobile genetic elements. This analysis could give some explanation to the multidrug resistance characteristics of bacteria colonizing the intestinal tract of dairy calves in the first few weeks of life.

Effect of passive transfer of immunity on growth performance of preweaned dairy calves.

The primary objective of this observational study was to examine the association between passive transfer of immunity and growth performance in preweaning calves. A secondary objective was to evaluate the utility of a heart girth tape (HGT) to estimate body weight (BW) in preweaning calves. A total of 142 Holstein calves were enrolled in this study. Blood samples were collected 24 to 48 hours after birth and serum immunoglobulin G (IgG) concentration for each calf was measured by radial immunodiffusion assay. Calf BW was determined at birth, at 21 days, and at weaning using an electronic scale (ES) and HGT. A significant positive association was detected between serum IgG and both BW at 21 days and average daily gain (ADG) from 0 to 21 days of life. Additionally, ADG from 0 to 42 days of life showed a trend toward an improved rate of gain as IgG concentration increased. The Pearson correlation coefficient between BW obtained from ES and HGT was 0.81 at birth, 0.86 at 21 days, and 0.83 at weaning. The mean differences between BW obtained from ES and HGT were -3.1 kg at birth, -3.2 kg at 21 days, and -7.7 kg at weaning. In conclusion, serum IgG concentration in neonatal calves is an important contributing factor for the variation in growth performance of preweaning calves. The HGT can be used to estimate the BW of preweaning calves but has a tendency to overestimate weight, especially at weaning compared to birth and 21 days of age.

L'objectif principal de cette étude observationnelle était d'examiner l'association entre le transfert passif d'immunité et les performances de croissance chez des veaux en période de pré-sevrage. Un second objectif était d'évaluer l'utilité d'un ruban pour mesurer la circonférence du tronc au niveau du coeur (HGT) pour évaluer le poids corporel (PC) chez des veaux en période de pré-sevrage. Un total de 142 veaux Holstein fut inclus dans l'étude. Des échantillons de sang furent obtenus 24 et 48 h après la naissance et la concentration en immunoglobine G (IgG) sérique de chaque veau fut mesurée par épreuve d'immunodiffusion radiale. Le PC des veaux fut déterminé à la naissance, à 21 j, et au moment du sevrage à l'aide d'une balance électronique (BÉ) et du HGT. Une association positive significative fut détectée entre la concentration sérique d'IgG et le PC à 21 j d'âge et le gain journalier moyen (GJM) entre les jours d'âge 0 à 21. De plus, le GJM des jours 0 à 42 montrait une tendance vers un taux de gain amélioré à mesure que les concentrations en IgG augmentaient. Le coefficient de corrélation de Pearson entre le PC obtenu via la BÉ et le HGT était de 0,81 à la naissance, 0,86 à 21 j, et 0,83 au moment du sevrage. Les différences moyennes des valeurs de PC obtenues par BÉ et HGT étaient de −3,1 kg à la naissance, −3,2 kg à 21 j, et −7,7 kg au sevrage. En conclusion, la concentration sérique en IgG chez les veaux nouveau-nés est un facteur contribuant important des variations des performances de croissance des veaux en période pré-sevrage. Le HGT peut être utilisé pour estimer le PC de veaux en période de pré-sevrage mais à tendance à surestimer le poids, et ce plus spécialement au moment du sevrage comparativement au moment de la naissance et à 21 j d'âge.(Traduit par Docteur Serge Messier).

Diagnostic performance of direct and indirect methods for assessing failure of transfer of passive immunity in dairy calves using latent class analysis.

Accurate diagnosis of failure of transfer of passive immunity (FTPI) in newborn calves is an essential component of dairy farm management plan. Several methods (direct and indirect) are available for diagnosis of FTPI in dairy calves. However, the indirect methods offer an advantage over the direct methods in not requiring an experienced veterinarian, rapid, cost efficient and can be performed under field-setting. The objective of this study was to estimate the diagnostic performance of radial immunodiffusion (RID) assay, transmission infrared (TIR) spectroscopy and digital Brix refractometer for diagnosis of FTPI in dairy calves using latent class models at four cut-off values of digital Brix refractometer. Holstein calves (n = 691) from 40 commercial dairy farms in the four Atlantic Canada provinces were blood-sampled and tested for detection of FTPI. Results showed that the number of calves with FTPI was 253 (36.6%) by RID, 194 (28.1%) by TIR and 204 (29.5%) by Brix refractometer at cut-off value of 8.2%. Estimates of SeRID was higher than SeTIR and SeBrix, at all Brix refractometer cut-offs, but with increase of Brix refractometer cut-off from 8.2 to 8.5%, SeRID and SeTIR were decreased from 96.0% (95% PCI: 88.0-99.0) and 79.0% (95% PCI: 70.0-85.0), to 92.0% (95% PCI: 77.0-99.0) and 74.0% (95% PCI: 61.0-82.0), respectively. SpRID and SpTIR were always higher than SpBrix at all tested cut-offs and were above 92.0%, and 96.0%, respectively. With increasing the cut-off of Brix refractometer from 8.2 to 8.5%, SeBrix estimate has remarkably increased from 79.0% (95% PCI: 70.0-96.0) to 95.0% (95% PCI: 87.0-100.0), respectively. Whilst, SpBrix was decreased from 95.0% (95% PCI: 91.0-98.0) at cut-off 8.2% to 84.0% (95% PCI: 78.0-94.0) at cut-off 8.5%. In conclusion, RID has a higher Se than TIR and Brix, if the latter is used with cut-offs of 8.2% or 8.3%. However, the higher the cut-off, the more comparable sensitivities of RID and digital Brix refractometer. The median estimate of SpTIR was always higher than SpRID and SpBrix at all tested cut-offs. However, the 95% confidence interval estimates of the three tests were overlapping across the tested cut-offs of digital Brix refractometer reflecting the inability to prefer a test over the other based on the Sp estimate.

Canadian National Dairy Study: Heifer calf management.

In the past decade, substantial changes have occurred in the way dairy heifer calves are managed. The objectives of this study, part of phase I of the 2015 Canadian National Dairy Study, were to examine heifer calf health and adoption of rearing practices, and to explore factors associated with different rearing strategies on Canadian dairy farms. The questionnaire was open to all licensed dairy producers in Canada and had a 12% response rate (n = 1,373). Fifty-one percent of respondents reported never allowing heifer calves to nurse their dam, and 17% always removed calves within 30 min of birth. Sixty-seven percent reported always feeding heifer calves 4 L of colostrum within 12 h of birth; 17% always fed colostrum between 2100 and 0400 h; 5% pasteurized all colostrum fed on farm. Seventy-seven percent of respondents reported calving and stillbirth information for 2014; the mean reported stillbirth rate was 4.9% (SD = 3.3). Forty percent housed calves in individual pens, 34% in group pens, 21% in individual hutches, 2% reported tethering calves, and 1% used group hutches. Of those who housed calves in groups, 59% reported a maximum group size of 3 to 10 calves, 31% reported a pair (2) of calves per pen or hutch, and 10% reported a group >10 calves. The maximum amount of milk offered to calves per day during the preweaned period was a mean of 8 L (SD = 3). Fifty percent of respondents reported mortality data for 2014; mean preweaning mortality was 6.4% (SD = 8.3), and postweaning mortality was 2.4% (SD = 4.4). Over 95% of producers reported disbudding practices; 86% used cautery, 11% used surgical amputation, and 9% used caustic paste. Twenty-eight percent reported disbudding at less than 3 wk of age, 60% at 3 to 8 wk, and 22% at 8 to 16 wk; 5% of respondents reported dehorning at more than 16 wk of age. Sixty-six percent of cautery users reported use of local anesthetic, 33% used sedation, and 25% used a nonsteroidal anti-inflammatory drug (NSAID). Multivariable regression models showed that the use of local anesthetic when disbudding calves was associated with social media activity (odds ratio = 2.3) and high-speed internet access (odds ratio = 2.0), whereas sedation was associated with geographic region, and NSAID use was associated with disbudding at more than 3 wk of age. Exploring heifer rearing management practices, including adoption of best practices, may help focus future education and extension efforts. Poor reporting of mortality data may reflect a lack of recordkeeping on farm.

Investigation of within- and between-herd variability of bovine leukaemia virus bulk tank milk antibody levels over different sampling intervals in the Canadian Maritimes.

Bulk tank milk (BTM) samples are used to determine the infection status and estimate dairy herd prevalence for bovine leukaemia virus (BLV) using an antibody ELISA assay. BLV ELISA variability between samples from the same herd or from different herds has not been investigated over long time periods. The main objective of this study was to determine the within-herd and between-herd variability of a BTM BLV ELISA assay over 1-month, 3-month, and 3-year sampling intervals. All of the Canadian Maritime region dairy herds (n = 523) that were active in 2013 and 2016 were included (83.9% and 86.9% of total herds in 2013 and 2016, respectively). BLV antibody levels were measured in three BTM samples collected at 1-month intervals in early 2013 as well as two BTM samples collected over a 3-month interval in early 2016. Random-effects models, with fixed effects for sample replicate and province and random effects for herd, were used to estimate the variability between BTM samples from the same herd and between herds for 1-month, 3-month, and 3-year sampling intervals. The majority of variability of BTM BLV ELISA results was seen between herds (1-month, 6.792 ±â€¯0.533; 3-month, 7.806 ±â€¯0.652; 3-year, 6.222 ±â€¯0.528). Unexplained variance between samples from the same herd, on square-root scale, was greatest for the 3-year (0.976 ±â€¯0.104), followed by the 1-month (0.611 ±â€¯0.035) then the 3-month (0.557 ±â€¯0.071) intervals. Variability of BTM antibody levels within the same herd was present but was much smaller than the variability between herds, and was greatest for the 3-year sampling interval. The 3-month sampling interval resulted in the least variability and is appropriate to use for estimating the baseline level of within-herd prevalence for BLV control programs. Knowledge of the baseline variability and within-herd prevalence can help to determine effectiveness of control programs when BTM sampling is repeated at longer intervals.

An observational cohort study on persistency of internal teat sealant residues in milk after calving in dairy cows.

Our objectives were to evaluate the prevalence of quarters with an observable internal teat sealant (ITS) plug at first milking following calving and investigate persistency of ITS residues in milk after calving. An observational cohort study was carried out on 557 quarters of 156 cows treated with ITS in 6 farms in Quebec, Canada. The presence of an ITS plug at first milking and ITS residues in milk at each milking were observed by producers. The effects of various factors on the odds of observing an ITS plug and persistency of ITS residues in milk were studied using generalized logistic mixed and generalized negative binomial mixed models, respectively. Milk samples were taken on the day before dry-off and on 2 occasions after calving for bacterial identification to detect intramammary infection (IMI) using bacteriological culture followed by MALDI-TOF identification. The association between the absence of an ITS plug and the presence of new IMI was assessed using a mixed logistic regression model. Internal teat sealant plugs after calving were more often observed in rear quarters and in quarters receiving ITS alone at drying-off versus antimicrobial and ITS. We observed an average (standard deviation) persistency of 4.0 d (2.3 d). When an ITS plug was still present at first milking (83% of quarters), the elimination of ITS residues in milk after calving was significantly longer (4.5 d, on average) compared with 1.2 d when an ITS plug was absent. In cows with an ITS plug at calving, we observed a higher number of days of excretion in older cows. When a plug could not be observed, rear quarters, older cows, and cows with a long dry period duration excreted ITS residues for a significantly longer period. The lack of a significant association between the absence of a plug and the odds of new IMI at calving suggests that despite the loss of the plug, cows were still protected against new IMI. Although we were able to highlight some statistically significant risk factors explaining persistency of ITS residues following calving, observed differences were often relatively small and, perhaps, not clinically relevant. In conclusion, an ITS plug was present until first milking after calving for 83% quarters, quarters without an ITS plug at first milking appeared to have been protected from new IMI, and ITS residues could be observed in milk up to 12 d in milk.

Immunogenicity of PtpA secreted during Mycobacterium avium ssp. paratuberculosis infection in cattle.

AIMS: Mycobacterium avium subsp. paratuberculosis (MAP) is the etiological agent of Johne's disease. To survive within host macrophages, the pathogen secretes a battery of proteins to interfere with the immunological response of the host. One of these proteins is tyrosine phosphate A (PtpA), which has been identified as a secreted protein critical for survival of its close relative M. tuberculosis within infected macrophages. METHODS AND RESULTS: In this study, the immune response to recombinant PtpA used as an antigen was investigated in a cohort of ∼1000 cows infected with MAP compared to negative control animals using ELISA. The sera from MAP-infected cows had significantly higher levels of antibodies against PtpA when compared to uninfected cows. CONCLUSIONS: The data presented here indicate that the antibodies produced against PtpA are sensitive enough to detect infected animals before the appearance of the disease symptoms. SIGNIFICANCE AND IMPACT OF STUDY: The use of PtpA as an antigen can be developed as an early diagnostic test. Moreover, PtpA is a candidate antigen for detection of humoral immune responses in cows infected with MAP.

Protein Kinase G Induces an Immune Response in Cows Exposed to Mycobacterium avium Subsp. paratuberculosis.

To establish infection, pathogens secrete virulence factors, such as protein kinases and phosphatases, to modulate the signal transduction pathways used by host cells to initiate immune response. The protein MAP3893c is annotated in the genome sequence of Mycobacterium avium subspecies paratuberculosis (MAP), the causative agent of Johne's disease, as the serine/threonine protein kinase G (PknG). In this work, we report that PknG is a functional kinase that is secreted within macrophages at early stages of infection. The antigen is able to induce an immune response from cattle exposed to MAP in the form of interferon gamma production after stimulation of whole blood with PknG. These findings suggest that PknG may contribute to the pathogenesis of MAP by phosphorylating macrophage signalling and/or adaptor molecules as observed with other pathogenic mycobacterial species.

Salmonella enterica and extended-spectrum cephalosporin-resistant Escherichia coli recovered from Holstein dairy calves from 8 farms in New Brunswick, Canada.

This study was carried out to determine the frequency of fecal carriage, antimicrobial susceptibility, and resistance genes in Salmonella enterica and Escherichia coli with reduced susceptibility to extended-spectrum cephalosporins (ESC) isolated from 488 dairy calves from 8 farms in New Brunswick, Canada. Both S. enterica and E. coli with reduced susceptibility to ESC were isolated using selective culture. Minimum inhibitory concentrations to a panel of antimicrobial drugs were determined for randomly selected E. coli isolates and all of the Salmonella isolates. Multiplex PCR were conducted on the selected ESC-resistant E. coli to assess the ß-lactamase resistance genes (blaCTX-M, blaCMY-2, blaSHV, and blaTEM) and plasmid-mediated qnrB and qnrS resistant genes. Information on ceftiofur use and other farm management practices were collected by the use of a questionnaire to determine the risk factors for the fecal recovery of E. coli with reduced susceptibility to ESC. Salmonella enterica frequency in calves' fecal samples was 3.3%, and all were pansusceptible. Salmonella isolates belonged to 3 serovars namely Salmonella Senftenberg, Salmonella Typhimurium, and Salmonella Derby. The frequency of fecal carriage of E. coli with reduced susceptibility to ESC in calves was 81.2%. Of the selected isolates (n = 100), all were multi-drug resistant, whereas 88% were ESC resistant based on minimum inhibitory concentration testing. From the selected ESC-resistant E. coli isolates, blaTEM was detected in 84.1%, blaCMY-2 was detected in 52.2%, blaCTXM groups were detected in 30.7%, and blaSHV was detected in 1.1% of isolates. Plasmid-mediated quinolone resistance genes were identified in 7 of 9 isolates resistant to quinolones. Five isolates were positive for qnrB, whereas 2 isolates were positive for both qnrB and qnrS. Whereas neonatal calves [odds ratio (OR) = 2.42, 95% confidence interval (CI): 1.87-3.12], regular ceftiofur use on the farm (OR = 3.83, 95% CI: 2.29-6.39), feeding of unpasteurized nonsalable milk (OR = 1.6, 95% CI: 1.18-2.18), and use of florfenicol (OR = 2.02, 95% CI: 1.43-2.86) were statistically associated with fecal recovery of E. coli with reduced susceptibility to ESC, use of ceftiofur for the treatment of respiratory diseases (OR = 0.57, 95% CI: 0.41-0.79) was statistically associated with decreased recovery of E. coli with reduced susceptibility to ESC. This study has provided information on the resistance genes associated with the occurrence of ESC and fluoroquinolone resistance in dairy calves within this region.

Application of transmission infrared spectroscopy and partial least squares regression to predict immunoglobulin G concentration in dairy and beef cow colostrum.

The objective of this study was to explore the potential of transmission infrared (TIR) spectroscopy in combination with partial least squares regression (PLSR) for quantification of dairy and beef cow colostral immunoglobulin G (IgG) concentration and assessment of colostrum quality. A total of 430 colostrum samples were collected from dairy (n = 235) and beef (n = 195) cows and tested by a radial immunodiffusion (RID) assay and TIR spectroscopy. Colostral IgG concentrations obtained by the RID assay were linked to the preprocessed spectra and divided into combined and prediction data sets. Three PLSR calibration models were built: one for the dairy cow colostrum only, the second for beef cow colostrum only, and the third for the merged dairy and beef cow colostrum. The predictive performance of each model was evaluated separately using the independent prediction data set. The Pearson correlation coefficients between IgG concentrations as determined by the TIR-based assay and the RID assay were 0.84 for dairy cow colostrum, 0.88 for beef cow colostrum, and 0.92 for the merged set of dairy and beef cow colostrum. The average of the differences between colostral IgG concentrations obtained by the RID- and TIR-based assays were -3.5, 2.7, and 1.4 g/L for dairy, beef, and merged colostrum samples, respectively. Further, the average relative error of the colostral IgG predicted by the TIR spectroscopy from the RID assay was 5% for dairy cow, 1.2% for beef cow, and 0.8% for the merged data set. The average intra-assay CV% of the IgG concentration predicted by the TIR-based method were 3.2%, 2.5%, and 6.9% for dairy cow, beef cow, and merged data set, respectively.The utility of TIR method for assessment of colostrum quality was evaluated using the entire data set and showed that TIR spectroscopy accurately identified the quality status of 91% of dairy cow colostrum, 95% of beef cow colostrum, and 89% and 93% of the merged dairy and beef cow colostrum samples, respectively. The results showed that TIR spectroscopy demonstrates potential as a simple, rapid, and cost-efficient method for use as an estimate of IgG concentration in dairy and beef cow colostrum samples and assessment of colostrum quality. The results also showed that merging the dairy and beef cow colostrum sample data sets improved the predictive ability of the TIR spectroscopy.

Distribution of non-aureus staphylococci species in udder quarters with low and high somatic cell count, and clinical mastitis.

The effect of non-aureus staphylococci (NAS) in bovine mammary health is controversial. Overall, NAS intramammary infections (IMI) increase somatic cell count (SCC), with an effect categorized as mild, mostly causing subclinical or mild to moderate clinical mastitis. However, based on recent studies, specific NAS may affect the udder more severely. Some of these apparent discrepancies could be attributed to the large number of species that compose the NAS group. The objectives of this study were to determine (1) the SCC of quarters infected by individual NAS species compared with NAS as a group, culture-negative, and major pathogen-infected quarters; (2) the distribution of NAS species isolated from quarters with low SCC (<200,000 cells/mL) and high SCC (≥200,000 cells/mL), and clinical mastitis; and (3) the prevalence of NAS species across quarters with low and high SCC. A total of 5,507 NAS isolates, 3,561 from low SCC quarters, 1,873 from high SCC quarters, and 73 from clinical mastitis cases, were obtained from the National Cohort of Dairy Farms of the Canadian Bovine Mastitis Research Network. Of quarters with low SCC, high SCC, or clinical mastitis, 7.6, 18.5, and 4.3% were NAS positive, respectively. The effect of NAS IMI on SCC was estimated using mixed-effect linear regression; prevalence of NAS IMI was estimated using Bayesian analyses. Mean SCC of NAS-positive quarters was 70,000 cells/mL, which was higher than culture-negative quarters (32,000 cells/mL) and lower than major pathogen-positive quarters (129,000 to 183,000 cells/mL). Compared with other NAS species, SCC was highest in quarters positive for Staphylococcus capitis, Staphylococcus gallinarum, Staphylococcus hyicus, Staphylococcus agnetis, or Staphylococcus simulans. In NAS-positive quarters, Staphylococcus xylosus (12.6%), Staphylococcus cohnii (3.1%), and Staphylococcus equorum (0.6%) were more frequently isolated from quarters with low SCC than other NAS species, whereas Staphylococcus sciuri (14%) was most frequently isolated from clinical mastitis cases. Finally, in NAS-positive quarters, Staphylococcus chromogenes, S. simulans, Staphylococcus epidermidis, and Staphylococcus haemolyticus were isolated with similar frequency from among low SCC and high SCC quarters and clinical mastitis cases. Staphylococcus chromogenes, S. simulans, S. xylosus, S. haemolyticus, S. epidermidis, S. agnetis, Staphylococcus arlettae, S. capitis, S. gallinarum, S. sciuri, and Staphylococcus warneri were more prevalent in high than in low SCC quarters. Because the NAS are a large, heterogeneous group, considering them as a single group rather than at the species, or even subspecies level, has undoubtedly contributed to apparent discrepancies among studies as to their distribution and importance in IMI and mastitis.

Assessment of the relative sensitivity of milk ELISA for detection of Mycobacterium avium ssp. paratuberculosis infectious dairy cows.

Milk ELISA are commonly used for detection of Mycobacterium avium ssp. paratuberculosis (MAP) antibodies in dairy cows, due to low cost and quick processing for large numbers of samples. However, low sensitivity and variations from host and environmental factors can impede detection of MAP antibodies at early disease stages. The objectives of our study were to assess the sensitivity of milk ELISA in comparison with fecal tests and to evaluate how detectable antibody concentrations in milk vary with changes in fecal shedding of MAP, cow age, cow parity, days in milk, and time of year. To compare the sensitivity of a commercial milk ELISA with solid and broth fecal culture and with fecal real-time PCR, a longitudinal study was performed for the identification of MAP-infectious animals as determined by prior fecal testing for MAP shedding. In addition, associations between variation in milk MAP ELISA score and changes in fecal MAP shedding, host age, days in milk, and season were evaluated. Monthly milk and fecal samples were collected over 1 yr from 46 cows that were previously shedding MAP in their feces. Sensitivity of milk ELISA was 29.9% (95% CI: 24.8 to 35.1%), compared with 46.7% (40.7 to 52.7%) for fecal solid culture, 55.0% (49.3 to 60.7%) for fecal broth culture, and 78.4% (73.3 to 83.1%) for fecal direct real-time PCR. The effect of stage of lactation could not be separated from the effect of season, with increased milk ELISA scores at greater days in milk in winter. However, unpredictable monthly variations in results were observed among the 3 assays for individual cow testing, which highlights the importance of identifying patterns in pathogen and antibody detection over time in MAP-positive herds.

Lifetime effects of infection with bovine leukemia virus on longevity and milk production of dairy cows.

Enzootic bovine leukosis (EBL) is an economically important disease of dairy cattle caused by bovine leukemia virus (BLV). The economic impacts of the infection have been debated in the literature. The present study was conducted to determine the lifetime effects of BLV infection on longevity and milk production of dairy cows in Canada. The data were aggregated from a combination of two data sets: 1) BLV serum-ELISA test results from Canada-wide surveys of production limiting diseases, which took place between 1998 and 2003 in 8 provinces, and 2) longitudinal production data for all cows in the former study, extracted from the Canadian dairy herd improvement database. All participant cows had been culled or died by the onset of this study. A historical cohort study was designed, including cows which tested positive to BLV-antibodies in their first lactation (positive cohort, n=1858) and cows which tested negative in their second or later lactations (negative cohort, n=2194). To assess the impacts of infection with BLV on longevity (the number of lifetime lactations), a discrete-time survival analysis was carried out. The effect of BLV on the lifetime milk production (the sum of all life 305-day milk production) was evaluated using a multilevel linear regression model. Overall, 4052 cows from 348 herds met the eligibility criteria and were enrolled in the study. In the longevity model, the interaction term between time (lactation number) and BLV-status was highly significant. Cows which were positive to BLV had consistently greater probabilities of being culled (or dying) than the test-negative cows. In the milk production model, the interaction term between BLV-status and longevity of the cows was highly significant; indicating that lifetime BLV effects on the total milk production was dependent on the lactation in which the study cows were culled/died. Infected cows with 2 and 3 lactations showed significantly lower life milk productions [-2554kg (-3609 to -1500) and -1171kg (-2051 to -292), respectively] compared with their negative counterparts with 2 and 3 lactations. As the cows lived longer (>3 lactations), the differences in life milk production between the two cohorts were no longer significant. Overall, it was predicted that the test-positive cows produced substantially lower milk compared to the test-negative cows throughout their study lifespans. With the high prevalence of BLV in Canadian dairy cows and its detrimental economic impacts, pursuing broad-based control programs in Canada should be evaluated.