Effects of simplified group housing on behavior, welfare, growth performance, and health of preweaned dairy calves on a California dairy.

Most US dairy calves are raised in individual hutches for biocontainment purposes and to facilitate monitoring and handling of calves. However, individual hutches typically restrict calves' activity and social interactions. Previous studies showed that group housing (GH) is beneficial to calf welfare and is associated with social benefits. The adoption of GH on dairies is hindered by several concerns, with the primary concern being the potential for increased transmission of diseases due to heightened calf-to-calf contact. In light of this, our study aimed to compare the behavior, health, and growth outcomes of calves housed in groups of 3 to individually housed (IH) calves during the preweaning period. A total of 42 Holstein heifer calves on a commercial dairy in Northern California were enrolled in groups of 3 to different housing treatments; IH (n = 21) or GH (n = 21) between July and October 2020. Each treatment was composed of 7 groups of 3 calves each. Calves in the GH treatment were housed in groups of 3 from 6 to 10 d until 70 d of age. Individual pens consisted of one polyethylene hutch with a 1.5 m × 1.2 m outside exercise area. Group pens were constructed by assembling 3 polyethylene hutches with a 1.5 m × 3.6 m outside exercise area of wire panel fencing. Calves were weighed and measured for height at birth and weaning. Diarrhea and bovine respiratory disease (BRD) scores were recorded daily throughout the preweaning period. Cumulative incidence and hazard ratios were estimated for BRD and diarrhea for GH and IH. A mixed model with pen as a random effect was specified to evaluate the effect of treatment. Group-housed calves gained 0.64 ± 0.02 kg/d while IH calves gained 0.65 ± 0.02 kg/d. Similarly, there was no evidence for treatment differences in withers height gain in GH calves (0.22 ± 0.01 cm/d) compared with IH calves (0.21 ± 0.01 cm/d). The cumulative incidence of BRD based on the California scoring system in GH calves was 75 ± 9.68% compared with 66.66 ± 10.28% in IH calves. Group-housed calves had a BRD hazard of 1.14 times that of IH calves (95% CI: 1.21-2.40). The cumulative incidence of diarrhea (fecal score 3) in GH calves was 100% in comparison to 95.20% ± 4.66% in IH calves. The mean proportion of scan observations of calves feeding on concentrates was significantly higher in GH (0.145 ± 0.004/h) compared with IH calves (0.076 ± 0.003/h) during the preweaning period. The study results provide evidence that this simplified GH system provides benefits of GH without detrimental short-term effects on calf growth and health during the preweaning period.

Development and comparison of loop-mediated isothermal amplification and quantitative polymerase chain reaction assays for the detection of Mycoplasma bovis in milk.

Bovine mastitis is an economic burden for dairies worldwide. Mycoplasma species, and especially Mycoplasma bovis, are among the most important causative agents, and rapid, precise, and low-cost methods for Mycoplasma detection are urgently needed. For this purpose, loop-mediated isothermal amplification (LAMP) and quantitative PCR (qPCR) assays were developed and compared. The LAMP assay was designed and primer concentrations optimized to M. bovis oppD, encoding oligopeptide permease D. For qPCR, a Taqman assay (Applied Biosystems, Carlsbad, CA) targeting M. bovis gltX, encoding glutamate transfer RNA ligase, was optimized for primer concentration, annealing temperature, and DNA polymerase. Both assays were similarly sensitive, with a detection limit of approximately 104 to 105M. bovis cells/mL. Both assays were also successful in confirming M. bovis identity in laboratory culture suspensions and in bovine milk. The LAMP and qPCR assays combined with the MoBio DNA extraction kit (MoBio Laboratories Inc., Carlsbad, CA) resulted in the correct detection of 13 out of 13 M. bovis isolates and 14 out of 16 M. bovis-positive milk samples collected from commercial dairies in California. When combined with the PrepMan Ultra reagent (Applied Biosystems), the qPCR assay resulted in confirming 21 out of 21 M. bovis-positive milk samples. Comparison of the assays to milk containing either Mycoplasma arginini, Mycoplasma bovigenitalium, Mycoplasma californicum, M. alkalescens, or Acholeplasma laidlawii or milk lacking any detectable Mycoplasma species or relatives resulted in 3 out of 17 (LAMP with MoBio), 1 out of 17 (qPCR with MoBio), and 2 out of 36 (qPCR with PrepMan Ultra) false positives. Overall, the qPCR assay was more robust than LAMP and could be used on DNA recovered from milk prepared with the PrepMan Ultra reagent, a method that does not include a DNA purification step. The use of this qPCR method enables M. bovis detection in bovine milk in 40 to 55 min, and therefore provides new opportunities to accelerate and simplify M. bovis detection in unpasteurized milk to reduce the incidence of M. bovis mastitis outbreaks.

Development of a clinical scoring system for bovine respiratory disease in weaned dairy calves.

Clinical scoring systems for bovine respiratory disease (BRD) in weaned dairy calves have been developed in the past with calves experimentally infected with specific respiratory pathogens. In this prevalent case control study, a BRD clinical scoring system for weaned calves was developed using field data from 689 dairy calves housed in group pens on 5 dairies in California. Of the 689 calves in the study, 89 were selected because they appeared sick based on the display of lethargy, depression, or separation from the group, whereas the remaining 600 were randomly selected. Clinical signs were recorded for all calves, and BRD case status was determined by thoracic auscultation and ultrasound examinations, which were interpreted in parallel. Of the 689 calves, 238 were identified as BRD cases. Five survey-adjusted generalized linear mixed models with a logit link function, calf as the unit of analysis, and dairy as a random intercept were assessed using 3-fold cross-validation. The best model chosen based on performance and parsimony contained the variables cough (2 points), abnormal respiration (1 point), low body condition (5 points), sunken eyes (4 points), and a 24-h ambient temperature range >15°C (1 point) with a 2-point cutoff for a BRD suspect score. An alternative model did not contain a score for the covariate 24-h ambient temperature range and had a 1-point cutoff. The best model was tested on 174 observations not used for model training and resulted in 77.0% screening sensitivity, 100% diagnostic sensitivity, and 61.9% specificity. Adding rectal temperature ≥39.2°C (102.5°F) as a second-tier test increased specificity to 76.7% and lowered the screening sensitivity to 64.8% and diagnostic sensitivity to 76.9%. The alternative model had a screening sensitivity of 84.2%, diagnostic sensitivity of 100%, and specificity of 45.7%. Adding rectal temperature ≥39.2°C (102.5°F) as a second-tier test for score-positive animals improved specificity of the alternative model to 62.6% while lowering its screening sensitivity to 70.5% and diagnostic sensitivity to 76.9%. Use of a 2-tier California BRD postweaning scoring system may provide producers and veterinarians with a new tool to monitor BRD in group-housed dairy calves. Furthermore, the scoring system may aid in judicious medical intervention for BRD cases and reduce unnecessary treatments of animals with antimicrobials.

Reliability of sampling strategies for measuring dairy cattle welfare on commercial farms.

Our objective was to evaluate how the proportion of high-producing lactating cows sampled on each farm and the selection method affect prevalence estimates for animal-based measures. We assessed the entire high-producing pen (days in milk <100; range = 81-241 cows) on 10 California farms using measures from the Welfare Quality Protocol for Cattle. Cows were restrained in head locks and visually evaluated for body condition, dirtiness, skin alterations (hair loss, lesions, or swelling), discharge (ocular, nasal, vulvar), diarrhea, and impaired respiration. Lameness was scored upon release. Prevalence was calculated as a percentage of assessed cows. The most common conditions were dirty hindquarters (33.5 ± 10.7%, mean ± standard deviation) and lesions or swelling on the carpal joint (34.4 ± 7.0%) and hock (26.4 ± 16.7%). Diarrhea (8.0 ± 5.8%), lameness (moderate = 7.3 ± 4.7%, severe = 2.2 ± 2.2%), and neck (5.8 ± 12.6%), flank (4.5 ± 5.0%), or hindquarter alterations (5.5 ± 3.9%) were less common. Very fat cows, vulvar discharge, and impaired respiration were rare (≤1%) and were excluded from further analysis. Four sampling strategies were used to generate 20 estimates for each animal-based measure. The strategies were (1) selecting every 10th, 5th, 4th, 3rd, 2nd, 2 of 3, or 3 of 4 cows at the feed bunk (7 estimates/measure); (2) randomly selecting 7 matching proportions of the pen; (3) randomly selecting cows using 3 sample size calculations from the Welfare Quality Protocol; and (4) selecting the first, middle, or final third of cows exiting the milking parlor. Estimates were compared with true values using regression analysis and were considered accurate if they met 3 criteria: the coefficient of determination was ≥0.9 and the slope and intercept did not differ significantly from 1 and 0, respectively. All estimates met the slope and intercept criteria, whereas the coefficient of determination increased when more cows were sampled. All estimates were accurate for neck alterations, ocular discharge (22.2 ± 27.4%), and carpal joint hair loss (14.1 ± 17.4%). Selecting a third of the milking order or using the Welfare Quality sample size calculations failed to accurately estimate all measures simultaneously. However, all estimates were accurate when selecting at least 2 of every 3 cows locked at the feed bunk. Using restraint position at the feed bunk did not differ systematically from computer-selecting the same proportion of cows randomly, and the former may be a simpler approach for welfare assessments.

Susceptibility loci revealed for bovine respiratory disease complex in pre-weaned holstein calves.

BACKGROUND: Bovine respiratory disease complex (BRDC) is an infectious disease of cattle that is caused by a combination of viral and/or bacterial pathogens. Selection for cattle with reduced susceptibility to respiratory disease would provide a permanent tool for reducing the prevalence of BRDC. The objective of this study was to identify BRDC susceptibility loci in pre-weaned Holstein calves as a prerequisite to using genetic improvement as a tool for decreasing the prevalence of BRDC. High density SNP genotyping with the Illumina BovineHD BeadChip was conducted on 1257 male and 757 female Holstein calves from California (CA), and 767 calves identified as female from New Mexico (NM). Of these, 1382 were classified as BRDC cases, and 1396 were classified as controls, with all phenotypes assigned using the McGuirk health scoring system. During the acquisition of blood for DNA isolation, two deep pharyngeal and one mid-nasal diagnostic swab were obtained from each calf for the identification of bacterial and viral pathogens. Genome-wide association analyses were conducted using four analytical approaches (EIGENSTRAT, EMMAX-GRM, GBLUP and FvR). The most strongly associated SNPs from each individual analysis were ranked and evaluated for concordance. The heritability of susceptibility to BRDC in pre-weaned Holstein calves was estimated. RESULTS: The four statistical approaches produced highly concordant results for 373 top ranked SNPs that defined 126 chromosomal regions for the CA population. Similarly, in NM, 370 SNPs defined 138 genomic regions that were identified by all four approaches. When the two populations were combined (i.e., CA + NM) and analyzed, 324 SNPs defined 116 genomic regions that were associated with BRDC across all analytical methods. Heritability estimates for BRDC were 21% for both CA and NM as individual populations, but declined to 13% when the populations were combined. CONCLUSIONS: Four analytical approaches utilizing both single and multi-marker association methods revealed common genomic regions associated with BRDC susceptibility that can be further characterized and used for genomic selection. Moderate heritability estimates were observed for BRDC susceptibility in pre-weaned Holstein calves, thereby supporting the application of genomic selection to reduce the prevalence of BRDC in U.S. Holsteins.

Agreement among deep nasopharyngeal sampling culture results for 3 different swab types in preweaning dairy calves.

Accurate isolation and identification of pathogens for an animal with bovine respiratory disease are of critical importance to direct appropriate decision-making related to the treatment of individual animals, as well as control and prevention options in a herd setting. The objective of this study was to compare nasopharyngeal sampling approaches to evaluate accuracy and agreement for the recovery of Mannheimia haemolytica (MH) and Pasteurella multocida (PM) from deep nasopharyngeal swabs (DNS) using 3 different swabs. Deep nasopharyngeal samples were collected from 45 dairy calves using 3 swabs: (1) double-guarded culture swab (DGS); (2) single-guarded culture swab (SGS); and (3) unguarded culture swab (UGS). To evaluate the degree of agreement between DGS, SGS, and UGS, culture results were compared for each calf sampled by using a kappa agreement test. Overall, findings from our study support that when using either SGS or DGS for DNS sampling of preweaning calves, a high agreement for recovery of PM is observed. A low recovery of MH was observed in the study, limiting the conclusion comparing the 3 DNS methods. Use of UGS is considered a potential alternative; however, a higher percentage of polymicrobial growth was found with UGS samples.

Effect of dry cow therapy on antimicrobial resistance of mastitis pathogens post-calving.

The aim of this study was to evaluate the effect of dry cow therapy (DCT) on the antimicrobial resistance (AMR) profile of mastitis pathogens post-calving. A repository of isolates based on a DCT trial was utilized for the current study. A stratified random survey sample of cows from the trial were identified within the strata of season, herd, and trial treatment resulting in 382 cows. All isolates from the 382 cows were selected for the current study, which identified 566 isolates from milk samples collected at dry off (S1), post-calving (S2), and at the first clinical mastitis event up to 150 days in milk (S3). The AMR profiles were determined using broth microdilution method. Less than 10% of the coagulase-negative Staphylococcus species (CNS) isolates (n = 421) were resistant to tetracycline, ceftiofur, penicillin/novobiocin or erythromycin, while higher proportions of resistance to sulfadimethoxine (72%) and penicillin (28%) were observed. All Staphylococcus aureus (S. aureus) isolates (n = 4) were susceptible to all tested AMD except sulfadimethoxine, to which all isolates were resistant. Similarly, all Streptococcus spp. (n = 37) were susceptible to penicillin, penicillin/novobiocin, and ampicillin while resistant to tetracycline (17%). All coliforms (n = 21) were susceptible to ceftiofur, but resistance was recorded for sulfadimethoxine (70%), cephalothin (56%), and tetracycline (43%). The increased resistance percent from S1 to S2 was observed in CNS isolates from AMD-treated cows, with the highest increase recorded for penicillin (12.2%). Parametric survival interval regression models were used to explore the association between antimicrobial drug (AMD) therapy at dry off and the AMR phenotype post-calving. The accelerated failure-time metric was adopted to minimum inhibitory concentration measurements to permit interpretation of model exponentiated coefficients. Models for cows with CNS isolated at both S1 and S2 showed increased resistance against cephalothin, oxacillin, and ceftiofur in cows that received DCT from the same drug class, or a class with a shared resistance mechanism. In contrast, resistance of CNS isolates to tetracycline were associated with any AMD therapy at dry off. Resistance of CNS isolates to Penicillin decreased in CNS isolates in cows that received any AMD therapy at dry off compared to those that didn't. The study provided evidence that dry-cow IMM AMD was associated with AMR post-calving.

Effect of Group Housing of Preweaned Dairy Calves: Health and Fecal Commensal Antimicrobial Resistance Outcomes.

The objectives of this study were to investigate the effects of group housing (three calves per group) on bovine respiratory disease (BRD), diarrhea and antimicrobial resistance (AMR) to fecal commensal Escherichia coli (EC) and enterococci/streptococci (ES). Our study comprised two arms, one experimental and one observational. In the experimental arm, preweaned calves on a California dairy were randomized to either individual (IND; n = 21) or group (GRP; n = 21) housing, using a modified California-style wooden hutch. The study period lasted from birth to 56 days of age, during which calves were health scored daily. Cumulative incidence and hazard ratios were estimated for disease. Antimicrobial resistance outcomes were assessed using a prospective cohort design; feces were collected from each calf three times per week and EC and ES were evaluated for AMR using the broth microdilution method against a panel of 19 antimicrobial drugs (AMD). Analysis of treatment records was used to select calves that had been exposed (EXP) to an AMD-treated calf. In GRP, exposure occurred when a calf was a hutchmate with an AMD-treated calf. In IND, exposure occurred when a calf was a neighbor with an AMD-treated calf (TRT). Age-matched unexposed calves (UNEXP) were then selected for comparison. Proportions of AMR in fecal commensals among EXP, UNEXP, and TRT calves were compared between GRP and IND. Accelerated failure time survival regression models were specified to compare differences in minimum inhibitory concentration (MIC) of fecal commensals between EXP and UNEXP calves within each of GRP and IND calves separately. Group calves had a BRD hazard 1.94 times greater that of IND calves (p = 0.03), using BRD treatment records as the outcome. For AMR in EC isolates, higher resistance to enrofloxacin was detected in enrofloxacin-EXP GRP isolates compared with enrofloxacin-EXP IND isolates, and UNEXP GRP calves had lower resistance to ceftiofur compared with enrofloxacin-EXP and enrofloxacin-TRT calves. A significant housing-by-time interaction was detected for EC ceftiofur MIC in EXP GRP calves at 4-14 days post exposure to enrofloxacin (MIC EXP-UNEXP: µg/mL (95% CI): 10.62 (1.17, 20.07)), compared with UNEXP calves. The findings of this study show an increase in BRD hazard for group-housed calves and an increase in ceftiofur resistance in group-housed calves exposed to an enrofloxacin-treated calf.

Agreement of antimicrobial susceptibility testing of Pasteurella multocida and Mannheimia haemolytica isolates from preweaned dairy calves with bovine respiratory disease.

OBJECTIVE: Evaluate agreement among the antimicrobial susceptibility profiles of Mannheimia haemolytica or Pasteurella multocida obtained by transtracheal wash, nasal swab, nasopharyngeal swab, and bronchoalveolar lavage. ANIMALS: 100 Holstein and Holstein-cross bull calves with bovine respiratory disease. METHODS: Calves > 30 days old with naturally occurring bovine respiratory disease were sampled sequentially by nasal swab, nasopharyngeal swab, transtracheal wash, and then bronchoalveolar lavage. Samples were cultured, and for each antimicrobial, the MIC of 50% and 90% of isolates was calculated, and isolates were categorized as susceptible or not. Categorical discrepancies were recorded. Percent positive agreement and kappa values were calculated between isolates for each of the sampling methods. RESULTS: Antimicrobial susceptibility varied by pathogen and resistance to enrofloxacin, florfenicol, tilmicosin, and spectinomycin was detected. Minor discrepancies were seen in up to 29% of classifications, with enrofloxacin, penicillin, and florfenicol more frequently represented than other drugs. Very major and major discrepancies were seen when comparing florfenicol (1.9%) and tulathromycin (3.8 to 4.9%) across sampling methods. Some variability was seen in agreement for enrofloxacin for several comparisons (8.3 to 18.4%). CLINICAL RELEVANCE: Susceptibility testing of isolates from 1 location of the respiratory tract can reliably represent susceptibility in other locations. Nevertheless, the potential for imperfect agreement between sampling methods does exist. The level of restraint available, the skill level of the person performing the sampling, the age and size of the animal, disease status, and treatment history all must be factored into which test is most appropriate for a given situation.

In vitro evaluation of the effect of transport medium, temperature, and time on the recovery of Mannheimia haemolytica and Pasteurella multocida.

Appropriate sample collection, storage conditions, and time for transport to the laboratory are important for an accurate diagnostic result. We evaluated the effects of transport storage medium type, time of storage, and storage temperatures on Mannheimia haemolytica (MH) and Pasteurella multocida (PM) recovery using an in vitro model simulation. A quantitative culture method, using colony-forming units per milliliter, was used to recover MH or PM by an in vitro model with cotton swabs. Three independent trials were conducted, in which cotton swabs were inoculated with MH or PM and placed in either (1) a sterile 15-mL polypropylene tube without transport medium (dry), (2) Amies culture medium with charcoal (ACM), or (3) Cary-Blair transport agar (CBA). Swabs were evaluated for recovery of MH or PM when stored at 3 temperatures (4°C, 23°C, or 36°C) and after storage for 8 h, 24 h, or 48 h. From all study group combinations, a total of 162 individual independent swabs were evaluated. The nonparametric Dunn all-pairs approach was used to compare the proportion of culturable bacteria, between the various storage media, temperature, and time point combinations. The proportion of MH in samples stored at 4°C was significantly higher for ACM and CBA than dry storage at 24 and 48 h. The MH samples stored at 36°C had a significantly higher proportion for ACM and CBA than dry storage at 24 h. The proportion of PM in samples stored at 4°C was significantly lower for ACM compared with dry at 8 h but significantly higher at 48 h. The PM samples stored at 23°C in ACM had a significantly higher proportion than dry samples at 24 h, and, at 48 h, ACM and CBA had a significantly higher proportion than the dry group. All swabs stored at 36°C for 48 h had a proportion close to zero, indicating decreasing diagnostic efficacy. These results support the use of transport media such as ACM and CBA for increasing the detection of PM and MH from samples, especially when samples are exposed to high temperatures. The combination of longer periods from collection of samples to diagnostic evaluation (>24 h) and higher storage temperatures (>23°C) were shown to significantly impair diagnostic accuracy.

Comparison of radiographic osteoarthritis scores in dogs less than 24 months or greater than 24 months following tibial plateau leveling osteotomy.

Radiographic osteoarthritis scores were determined in 60 dogs up to 3 years following tibial plateau leveling osteotomy. Radiographs taken immediately following surgery and at long-term follow-up 1 to 3 years later were evaluated by 2 certified radiologists using a modified 32-point osteoarthritis scale. Changes in osteoarthritis scores were evaluated by paired t-tests and regression analysis. Sub-groups of dogs were formed to evaluate if osteoarthritis scores changed differently for follow-up periods of < 24 months compared with those > 24 months. There was a significant increase in osteoarthritis score from post-operative to follow-up evaluations for all dogs studied. Regression analysis of the relationship of months after surgery to change in osteoarthritis score was not significant. These results indicate that osteoarthritis did progress following tibial plateau leveling osteotomy, but not in a linear fashion over time.

Comparaison des cotes radiographiques pour l'ostéoarthrite chez les chiens âgés de moins de 24 mois ou de plus de 24 mois après une ostéotomie de stabilisation du plateau tibial. Les cotes radiographiques d'ostéoarthrite ont été déterminées chez 60 chiens jusqu'à 3 ans après une ostéotomie de stabilisation du plateau tibial. Les radiographies prises immédiatement après la chirurgie et au suivi à long terme, de 1 à 3 ans plus tard, ont été évaluées par 2 radiologistes certifiés à l'aide d'une échelle d'ostéoarthrite modifiée de 32 points. Les changements des cotes d'ostéoarthrite ont été évalués à l'aide de tests de t pairés et d'analyses de régression. Des sous-groupes de chiens ont été formés afin d'évaluer si les cotes d'ostéoarthrite avaient évolué différemment pour les périodes de suivi de < 24 mois comparativement à celles de > 24 mois. Il y a eu une hausse importante de la cote d'ostéoarthrite entre les évaluations postopératoires et les évaluations de suivi pour tous les chiens examinés. L'analyse de régression de la relation entre le nombre de mois après la chirurgie et le changement de la cote d'ostéoarthrite n'était pas significative. Les résultats indiquent que l'ostéoarthrite a progressé après l'ostéotomie de stabilisation du plateau tibial, mais non d'une manière linéaire au fil du temps.(Traduit par Isabelle Vallières).

Factors Associated with Antimicrobial Stewardship Practices on California Dairies: One Year Post Senate Bill 27.

BACKGROUND: The current study is aimed at identifying the factors associated with antimicrobial drug (AMD) use and stewardship practices on conventional California (CA) dairies a year after CA Senate Bill 27. METHODS: Responses from 113 out of 1282 dairies mailed a questionnaire in 2019 were analyzed to estimate the associations between management practices and six outcomes including producer familiarity with medically important antimicrobial drugs (MIADs), restricted use of MIADs previously available over the counter (OTC), use of alternatives to AMD, changes in on-farm management practices, changes in AMD costs, and animal health status in dairies. RESULTS: Producers who reported having a veterinarian-client-patient relationship (VCPR) and tracking AMD withdrawal intervals had greater odds of being familiar with the MIADs. Producers who began or increased the use of preventive alternatives to AMD in 2019 had higher odds (OR = 3.23, p = 0.04) of decreased use of MIADs previously available OTC compared to those who did not. Changes in management practices to prevent disease outbreak and the use of diagnostics to guide treatment were associated with producer-reported improved animal health. In addition, our study identified record keeping (associated with familiarity with MIADs), use of alternatives to AMD (associated with management changes to prevent diseases and decreased AMD costs), and use of diagnostics in treatment decisions (associated with reported better animal health) as factors associated with AMD stewardship. CONCLUSIONS: Our survey findings can be incorporated in outreach education materials to promote antimicrobial stewardship practices in dairies.

Effectiveness of Intramammary Antibiotics, Internal Teat Sealants, or Both at Dry-Off in Dairy Cows: Milk Production and Somatic Cell Count Outcomes.

Mastitis is the greatest disease challenge for dairy producers, with substantial economic impacts due to lost milk production. Amongst the approaches implemented to control and prevent mastitis on dairies are vaccination, pre- and post-milking teat dips, and treatments at dry-off including intramammary antibiotics and teat sealants. The objectives of our study were to evaluate the effect of different treatments at dry-off on the subsequent lactation's milk production and somatic cell count (SCC). A single-blinded controlled block randomized clinical trial was conducted between December 2016 and August 2018 on eight herds from four of the top ten milk-producing counties in California: Tulare, Kings, Stanislaus, and San Joaquin. The trial was repeated with cows enrolled during the winter and summer seasons to account for seasonal variability. Eligible cows were treated at dry-off with either intramammary antibiotics (AB), internal teat sealant (TS), AB + TS, or did not receive any treatment (control), and were followed through 150 days in milk (DIM) post-calving. The milk production and SCC data were extracted from monthly test day milk records (Dairy Comp 305, Valley Ag Software, Tulare, CA, USA). Two-piece spline linear mixed models were used to model the milk production (kg) and natural logarithm-transformed SCC. After accounting for parity, breed, season, and dry period duration, the milk model showed a significant increase in milk production (1.84 kg/day) in cows treated with AB + TS at dry-off in comparison to controls. There was no significant difference in the milk produced by cows that received either AB or TS (0.12 kg/day, and 0.67 kg/day, respectively) in comparison to the untreated cows. Different dry cow treatments were associated with a significant reduction in ln SCC during the first 150 DIM. The greatest reduction was associated with using AB + TS, followed by AB, and finally TS in comparison to controls. Dairies with high SCC may benefit from treating cows at dry-off with AB, TS, or both.

Effectiveness of Intramammary Antibiotics, Internal Teat Sealants, or Both at Dry-Off in Dairy Cows: Clinical Mastitis and Culling Outcomes.

Intramammary antibiotic (AB) and internal teat sealants (TS) infusion at dry-off have been used to prevent intramammary infections (IMI) in dairy cows during the dry period and reduce the risk of mastitis during the dry period and subsequent lactation. A randomized clinal trial was completed on eight California dairy herds to estimate the effects of different dry cow therapies (AB, TS, AB + TS or None) on clinical mastitis and culling. A total of 1273 cows were randomized to one of the four treatment groups over summer and winter seasons. For each enrolled cow, microbiological testing was done on quarter milk samples collected from the first detection of clinical mastitis within the first 150 days in milk (DIM) in the subsequent lactation. Statistical analysis was done using generalized linear mixed models. There were no significant differences in the odds of clinical mastitis or culling between cows treated with AB, TS, or AB + TS compared to the controls. Dry cow therapy with AB and/or TS had no statistically significant effect on clinical mastitis and cow culling during the first 150 DIM.

Stable fly activity is associated with dairy management practices and seasonal weather conditions.

Stable flies (Stomoxys calcitrans) are blood-sucking insects commonly associated with cattle production systems worldwide and are known to cause severe irritation to cattle due to painful bites. Cattle react to biting stable flies with an aggregating behavior known as bunching. Bunching behavior reduces grazing or feed consumption and thus reduces cattle productivity and welfare. Cattle's fly-repelling behaviors include foot stomping, head tossing, tail switching and skin twitching. A longitudinal study was conducted in 2017 on 20 California dairies (average lactating herd size = 2,466 (SE±28.392)) during the stable fly season from April to July. The study objectives were to estimate the association between environmental factors and dairy characteristics including facility design, feed and manure management, total mixed ration (TMR) components fed to cattle, and operational pest management procedures and the outcome stable fly activity on California dairies. Stable fly activity was measured by counting stable flies on cow forelimbs (leg count) and on Alsynite traps (trap count) over the 13-week study period. Weekly leg counts were performed for cattle in lactating cow pens (31 pens from 10 study dairies) with counts made during the morning (AM) and again during the afternoon (PM). Trap counts were performed on all 20 study dairies. Data were analyzed using linear mixed models which revealed temporal variation in the average leg and trap counts with stable fly activity increasing from May to June and then decreasing to the lowest activity in July. Leg counts were higher during the afternoon compared to morning. Ambient temperatures ≤30°C and relative humidity (RH) measurements <50% were associated with higher leg and trap counts. Traps located at the periphery of study dairies had higher stable fly counts compared to traps located in the interior of the dairy. Cow pens with trees on the periphery had higher leg counts in comparison to pens away from trees. Specific TMR components were associated with both leg and trap counts. Dairies feeding by-products including almond hulls, wet distillers' grain, fruits, and vegetables had higher trap counts compared to dairies that did not feed these ingredients. At the pen level, pens with rations that contained straw had lower average leg counts compared to pens fed with rations that did not contain straw. A similar association was observed for pens with rations that contained wheat silage when ambient temperatures were ≤30°C. In contrast, pens with water added to the TMR while the RH was ≥50% had higher average leg counts compared to pens without water added to the TMR. Dairies that applied insecticides for fly control to their entire facility had lower trap counts compared to dairies that did not apply insecticides. Stable fly activity measured on California dairies using leg and trap counts varied according to the month, environmental factors, pen surroundings, trap location, TMR components, and insecticide use.

Etiology and risk factors for bovine respiratory disease in pre-weaned calves on California dairies and calf ranches.

Our study objective was to estimate the magnitude of association of BRD risk factors including failure of passive immunity transfer, sex, age, and the detection of suspected BRD etiological pathogens in pre-weaned dairy calves in California. A conditional logistic regression model and a mixed-effects logistic regression model were used to estimate the association of these potential risk factors with BRD from a matched and nested case-control studies, respectively. For each exposure covariate, the odds ratio (OR) is the ratio of odds of an exposure in a BRD calf (case) to that in a non-BRD calf (control). In the matched case-control study, an interaction term between failure of transfer of passive immunity and sex of calf showed that female calves were more negatively impacted by failure of transfer of passive immunity compared to male calves. The odds ratios comparing failure of transfer of passive immunity in BRD score positive calves versus controls for male calves was 1.34 (95 % CI: 0.87, 2.06) and was 2.47 (95 % CI: 1.54, 3.96) for female calves. The model odds ratios varied from 1.74 (95 % CI: 1.26, 2.42) for Mycoplasma spp. to 9.18 (95 % CI: 2.60, 32.40) for Histophilus somni, with Mannheimia haemolytica and Pasteurella multocida having an OR of 6.64 (95 % CI: 4.39, 10.03) and 6.53 (95 % CI: 4.44, 9.59), respectively. For bovine respiratory syncytial virus positive calves, the OR was 4.60 (95 % CI: 3.04, 6.97). Findings from the nested case-control study showed that based on thoracic ultrasonography findings consistent with BRD, the odds of a calf being 1 day older compared to a day younger were 1.01 (95 % CI: 1.00, 1.02) among BRD cases. For the bacterial and viral pathogens, the OR for Mycoplasma spp. and Pasteurella multocida were 1.85 (95 % CI: 1.24, 2.75) and 1.86 (95 % CI: 1.28, 2.71), respectively. The OR values for these pathogens were similar when both thoracic auscultation and ultrasound findings were used to detect cases of BRD. Based on positive scores for BRD using the California BRD scoring system, the OR for facility type, calf ranch versus dairy farm, was 3.17 (95 % CI: 1.43, 7.01), Mannheimia haemolytica was 3.50 (95 % CI: 2.00, 6.11), Pasteurella multocida was 1.78 (95 % CI: 1.21, 2.60), and bovine coronavirus was 2.61 (95 % CI: 1.85, 3.70). Results from both study designs showed the difference in relative contributions of age, sex, immune status, and pathogens in BRD occurrence between cases and controls in pre-weaned dairy calves.

Development of a multiplex qPCR assay for the simultaneous detection of Mycoplasma bovis, Mycoplasma species, and Acholeplasma laidlawii in milk.

Contagious bovine mastitis caused by Mycoplasma bovis and other Mycoplasma species including Mycoplasma californicum, Mycoplasma bovigenitalium, Mycoplasma alkalescens, Mycoplasma arginini, and Mycoplasma canadense is an economical obstacle affecting many dairy herds throughout California and elsewhere. Routine bacteriological culture-based assays for the pathogens are slow and subject to false-positive results due to the presence of the related, non-pathogenic species Acholeplasma laidlawii. To address the need for rapid and accurate detection methods, a new TaqMan multiplex, quantitative real-time PCR (qPCR) assay was developed that targets the 16S rRNA gene of Mycoplasma, rpoB gene of M. bovis, and the 16S to 23S rRNA intergenic transcribed spacer (ITS) region of A. laidlawii. qPCR amplification efficiency and range of detection were similar for individual assays in multiplex as when performed separately. The multiplex assay was able to distinguish between M. bovis and A. laidlawii as well as detect Mycoplasma spp. collectively, including Mycoplasma californicum, Mycoplasma bovigenitalium, Mycoplasma canadense, Mycoplasma arginini and Mycoplasma alkalescens. In milk, the lower limit of detection of M. bovis, M. californicum, and A. laidlawii with the multiplex assay was between 120 to 250 colony forming units (CFU) per mL. The assay was also able to simultaneously detect both M. bovis and A. laidlawii in milk when present in moderate (103 to 104 CFU/mL) to high (106 to 107 CFU/mL) quantities. Compared to laboratory culture-based methods, the multiplex qPCR diagnostic specificity (Sp) was 100% (95% CI [86.8-100]; n = 26) and diagnostic sensitivity (Se) was 92.3% (95% CI [74.9-99.1]; n = 26) for Mycoplasma species in milk samples collected from California dairy farms. Similarly, the Sp was 100% (95% CI [90.5-100]; n = 37) and Se was 93.3% (95% CI [68.1-99.8]; n = 15) for M. bovis. Our assay can detect and distinguish among M. bovis, other prevalent Mycoplasma spp., and non-pathogenic Acholeplasma laidlawii for effective identification and control of mycoplasma mastitis, ultimately supporting dairy cattle health and high-quality dairy products in California.

Effect of Antimicrobial Treatment on the Dynamics of Ceftiofur Resistance in Enterobacteriaceae from Adult California Dairy Cows.

Dairy farm use of antimicrobial drugs (AMD) is a risk for the selection of antimicrobial resistance (AMR); however, these resistance dynamics are not fully understood. A cohort study on two dairy farms enrolled 96 cows with their fecal samples collected three times weekly, for the first 60 days in milk. Enterobacteriaceae were enumerated by spiral plating samples onto MacConkey agar impregnated with 0, 1, 8, 16 and 30 µg/mL ceftiofur. Negative binomial regression analyzed AMR over time. The continuum of ceftiofur concentrations permitted estimation of the minimum inhibitory concentration (MIC) and analysis using interval regression. The most common systemic AMD was ceftiofur, administered in 94% of treatments (15/16 cows). Enterobacteriaceae did not grow in 88% of samples collected from non-AMD treated cows at 8 µg/mL ceftiofur. Samples from AMD treated cows had peak counts of resistant Enterobacteriaceae during AMD treatment and returned to baseline counts by 3-4 days post-treatment at 8 µg/mL. Sensitive Enterobacteriaceae (0-1 µg/mL ceftiofur) were reduced below pre-treated levels for 29-35 days post-AMD treatment. Population MIC peaked during AMD treatment and returned to baseline levels by 7-8 days. We conclude that the effect of systemic ceftiofur on the resistance of Enterobacteriaceae in early lactation dairy cows was limited in duration.

Survey on Antimicrobial Drug Use Practices in California Preweaned Dairy Calves.

The California (CA) dairy industry was surveyed in July 2017 to evaluate producers' knowledge and perceptions and antimicrobial drug (AMD) use in preweaned dairy calves following the implementation of the nationwide veterinary feed directive final rule (VFD) in January 2017 and prior to statewide implementation of CA Senate Bill (SB) 27 in January 2018. Together, these regulations require veterinary oversight for all uses of medically important antimicrobial drugs (MIADs) administered to livestock in CA. Survey questionnaire was mailed to 1,361 CA Grade A milk producing dairies and calf ranches across CA resulting in a 12% (169) response. Most respondents (83%) were aware of the VFD and SB 27 changes. Use of antibiotics was perceived as important (77%) in raising preweaned dairy calves and judicious use of antibiotics was ranked as the most important antimicrobial stewardship practice, amongst record keeping, observing withdrawal periods, having a valid Veterinarian-Client-Patient-Relationship (VCPR), and use of alternatives to antibiotics. Treating sick calves was the major indication for AMD use (90.5%); however, few producers reported use of antibiotics to control (12.7%) or prevent disease (11%). Neomycin sulfate, chlortetracycline, oxytetracycline and sulfamethazine were the most used AMD. The respondents reported a decreased use of AMD in milk (10%) and in solid feed (5%), and discontinuation of one or more AMDs used in milk (18.6%) or in solid feed (5%) post-VFD rule implementation in 2017. Most respondents reported keeping treatment records and the information recorded included date (82%), dose (44%) and route (15%) of AMD used. A few respondents reported they had initiated use of alternatives to AMDs, such as vitamins (32.6%), minerals (25.6%), herbal remedies (11.6%) and pathogen specific antibodies (7%), post-VFD. The limited changes noted in AMD use could be attributed to the short period between the implementation of the VFD and the time of the survey. Our study outcomes identified opportunities to improve AMD use practices, including record keeping and use of AMD alternatives, and provides a baseline for future evaluation of the impact of these regulatory changes, as well as guidance for the future recommendations on best practices to promote judicious AMD use.

Estimating the Rates of Acquisition and loss of Resistance of Enterobacteriaceae to Antimicrobial Drugs in Pre-Weaned Dairy Calves.

The objective of this study was to investigate the effect of the antimicrobial drugs (AMD) on the shedding of resistant Enterobacteriaceae in feces of pre-weaned dairy calves. The AMD considered were ceftiofur, administered parenterally, and neomycin sulfate added in milk replacer and fed to calves during the first 20 days of life. Fifty-five calves, aged one to three days, were enrolled and followed to 64 days. Fecal samples were collected three times/week and treatments recorded daily. Enterobacteriaceae were quantified for a subset of 33 calves using spiral plating on plain, ceftiofur supplemented, and neomycin supplemented MacConkey agar. Negative binomial models were used to predict the association between treatment with AMD and the gain and loss of Enterobacteriaceae resistance over time. Acquisition of resistance by the Enterobacteriaceae occurred during treatment and peaked between days three to four post-treatment before decreasing to below treatment levels at days seven to eight post-treatment. Acquisition of neomycin resistance was observed on the first sampling day (day four from the start of feeding medicated milk replacer) to day eight, followed by cyclical peaks until day 29, when the Enterobacteriaceae counts decreased below pre-treatment. Enterobacteriaceae resistance against both AMD increased after AMD administration and didn't return to pre-therapeutic status until seven or more days after therapy had been discontinued. The study findings provide valuable insights into the dynamics of Enterobacteriaceae under routine AMD use in calves.