Highly Pathogenic Avian Influenza A(H5N1) Clade 2.3.4.4b Virus Infection in Domestic Dairy Cattle and Cats, United States, 2024.

We report highly pathogenic avian influenza A(H5N1) virus in dairy cattle and cats in Kansas and Texas, United States, which reflects the continued spread of clade 2.3.4.4b viruses that entered the country in late 2021. Infected cattle experienced nonspecific illness, reduced feed intake and rumination, and an abrupt drop in milk production, but fatal systemic influenza infection developed in domestic cats fed raw (unpasteurized) colostrum and milk from affected cows. Cow-to-cow transmission appears to have occurred because infections were observed in cattle on Michigan, Idaho, and Ohio farms where avian influenza virus-infected cows were transported. Although the US Food and Drug Administration has indicated the commercial milk supply remains safe, the detection of influenza virus in unpasteurized bovine milk is a concern because of potential cross-species transmission. Continued surveillance of highly pathogenic avian influenza viruses in domestic production animals is needed to prevent cross-species and mammal-to-mammal transmission.

Pharmacokinetics of long-acting cephapirin and cloxacillin after intramammary administration in dairy goats.

Determining the pharmacokinetics of intramammary antimicrobials in goats can assist in predicting appropriate meat and milk withdrawal intervals for drugs that are effective at treating subclinical mastitis due to non-aureus Staphylococci during the dry period. Twenty-four healthy, lactating does were enrolled in this study. Half were administered 300 mg of cephapirin benzathine (ToMORROW, Boehringer Ingelheim Vetmedica, Duluth, GA) via intramammary infusion into each half of the udder. The remaining does had 500 mg cloxacillin benzathine (Orbenin DC, Merck & Co., Rahway, NJ) administered per half. Plasma was collected before treatment and for 7 days post-treatment followed by analysis via liquid chromatography with tandem mass spectroscopy. Pharmacokinetic parameters were determined using noncompartmental methods via commercial software (MonolixSuite). The mean maximum concentration (Cmax) of cephapirin of 0.073 µg/mL was noted at 7.06 h post-administration (Tmax). The area under the plasma concentration curve based on the final sampling point (AUClast) was 1.06 h × µg/mL. The mean residence time until the final sampling point (MRTlast) was 13.55 h. Mean terminal half-life (T½) of cephapirin was 6.98 h. In CLOX does, Cmax was 0.074 µg/mL with a Tmax of 18 h, AUClast was 5.71 h × µg/mL, T½ was 77.45 h, and MRTlast was 65.36 h. Despite both products being formulated with benzathine salts, marked differences were noted in pharmacokinetic parameters including AUC, T1/2, and MRTlast. This data will be used to plan sampling schedules for milk and tissue residue depletion studies for both products.

Whole-genome analysis of Klebsiella pneumoniae from bovine mastitis milk in the U.S.

Dairy cattle mastitis has long been one of the most common and costly diseases in the dairy industry worldwide, due to its significant impact on milk production and animal welfare. Among all mastitis causing bacterial pathogens, Klebsiella pneumoniae causes the largest milk loss. To better understand the genomic features of this population, 180 K. pneumoniae strains isolated from dairy cattle mastitis milk in 11 U.S. states were sequenced. The phylogenetic analysis classified all mastitis-causing K. pneumoniae into two major phylogroups, with exclusive predominance in phylogroup KpI. Analysis of more than 61 sequence types, 51 capsular types and 12 lipopolysaccharide O-antigen types revealed great genomic diversity of this K. pneumoniae population. Approximately 100 gene units in accessory genomes were detected with significantly higher prevalence in bovine mastitis strains, compared to human-sourced or dairy environmental strains. The most notable genes were identified associated with ferric citrate uptake, lactose fermentation and resistance to heavy metals. The acquired antimicrobial resistance genes were identified in sporadic mastitis strains. This comprehensive genomic epidemiological study provides insights for a better understanding of the virulence of mastitis-causing K. pneumoniae strains and may lead to the development of novel diagnostic tools and preventive strategies.

Comparative plasma and interstitial fluid pharmacokinetics and tissue residues of ceftiofur crystalline-free acid in cattle with induced coliform mastitis.

Ceftiofur (CEF) is a third-generation cephalosporin that is the most widely used antimicrobial in the dairy industry. Currently, violative meat residues in cull dairy cattle are commonly associated with CEF. One potential cause for violative residues is altered pharmacokinetics of the drug due to disease, which could increase the time needed for the residue to deplete. The objectives of this study were (a) to determine the absolute bioavailability of CEF crystalline-free acid (CFA) in healthy versus diseased cows; (b) to compare the plasma and interstitial fluid pharmacokinetics and plasma protein binding of CEF between healthy dairy cows and those with disease; and (c) to determine the CEF residue profile in tissues of diseased cows. For this trial, disease was induced through intramammary Escherichia coli infusion. Following disease induction and CEF CFA administration, for plasma concentrations, there was not a significant effect of treatment (p = 0.068), but the treatment-by-time interaction (p = 0.005) was significant. There was a significantly greater concentration of CEF in the plasma of the DIS cows at T2 hr (p = 0.002), T8 hr (p < 0.001), T12 hr (p = 0.001), and T16 hr (p = 0.002). For PK parameters in plasma, the slope of the terminal phase of the concentration versus time curve was significantly lower (p = 0.007), terminal half-life was significantly longer (p = 0.014), and apparent volume of distribution during the elimination phase was significantly higher (p = 0.028) diseased group. There was no difference in plasma protein binding of CEF and interstitial fluid pharmacokinetics. None of the cows had kidney CEF residues above the US tolerance level following observation of the drug's withdrawal period, but one cow with a larger apparent volume of distribution and longer terminal half-life had tissue residues slightly below the tolerance. Whereas these findings do not support the hypothesis that severely ill cows need longer withdrawal times, alterations in the terminal half-life suggest that it is theoretically possible.

The impact of pain on the pharmacokinetics of transdermal flunixin meglumine administered at the time of cautery dehorning in Holstein calves.

OBJECTIVE: To study the influence of pain on the pharmacokinetics and anti-inflammatory actions of transdermal flunixin administered at dehorning. STUDY DESIGN: Prospective, crossover, clinical study. ANIMALS: A total of 16 male Holstein calves, aged 6-8 weeks weighing 61.3 ± 6.6 kg. METHODS: Calves were randomly assigned to one of two treatments: transdermal flunixin and dehorning (PAIN) or transdermal flunixin and sham dehorning (NO PAIN). Flunixin meglumine (3.33 mg kg-1) was administered topically as a pour-on concurrently with hot iron dehorning or sham dehorning. The calves were subjected to the alternative treatment 14 days later. Blood samples were collected at predetermined time points up to 72 hours for measurement of plasma flunixin concentrations. Pharmacokinetics parameters were determined using noncompartmental analysis. Prostaglandin E2 (PGE2) concentration was determined using a commercial enzyme-linked immunosorbent assay. The 80% inhibition concentration (IC80) of PGE2 was determined using nonlinear regression. Pharmacokinetic data were statistically analyzed using paired t tests and Wilcoxon rank sums for nonparametric data. Flunixin and PGE2 concentrations were log transformed and analyzed using repeated measures. RESULTS: A total of 15 calves completed the study. Plasma half-life of flunixin was significantly longer in PAIN (10.09 hours) than NO PAIN (7.16 hours) (p = 0.0202). Bioavailability of transdermal flunixin was 30% and 37% in PAIN and NO PAIN, respectively (p = 0.097). Maximum plasma concentrations of flunixin were 0.95 and 1.16 µg mL-1 in PAIN and NO PAIN, respectively (p = 0.089). However, there was a treatment (PAIN versus NO PAIN) by time interaction (p = 0.0353). PGE2 concentrations were significantly lower in the PAIN treatment at 48 and 72 hours (p = 0.0092 and p = 0.0287, respectively). The IC80 of PGE2 by flunixin was similar in both treatments (p = 0.88). CONCLUSION AND CLINICAL RELEVANCE: Pain alters the pharmacokinetics and anti-inflammatory effects of transdermally administered flunixin.

Digital dermatitis: Natural lesion progression and regression in Holstein dairy cattle over 3 years.

Bovine digital dermatitis (DD) is a leading cause of lameness in dairy cattle in the United States, with prevalence estimates as high as 30%. Whereas clinical lesions have been well described, little is known about the morphologic changes that are associated with the early stages of lesion development from normal skin to clinical lesions. This study used the Iowa DD scoring system to evaluate the epidemiology of natural lesion development by digitally photographing the rear legs of a cohort of dairy cows over a 3-yr period. Sixty-one adult Holstein dairy cows were monitored for 1,032 cow foot-months. The incidence rate of lesion development was 4 lesions per 100 cow foot-months, with the average time for a lesion to develop being 133 d. Whereas 20% of the 1,678 foot observations exhibited clinical DD lesions, an additional 55% of all observations exhibited preclinical stage 1 and 2 lesions that were indicative of DD lesion development. Utilizing the dichotomous categorization of preclinical lesions in the Iowa DD scoring system, it was found that first-lactation heifers had a higher rate of the thickened and crusted "B" type lesions, whereas the ulcerative "A" type lesions were more likely to be identified in multiparous animals. For clinical DD lesions that received topical treatment, scoring of the post-treatment lesions using the Iowa DD scoring system was found to be useful in prognosticating both the risk of recrudescence and the time until recrudescence. Systemic disease, systemic antibiotic therapy, and periparturient stress were not associated with an increase or decrease in DD lesion scores. Treatment with a single topical tetracycline wrap was associated with a significant decrease (-1.17) in DD lesion score. The results of this study demonstrate that the complex morphologic changes associated with digital dermatitis can be readily classified using the Iowa DD scoring system and the scores can be used to predict and monitor the effects of treatment and prevention measures.

Deep sequencing analysis reveals temporal microbiota changes associated with development of bovine digital dermatitis.

Bovine digital dermatitis (DD) is a leading cause of lameness in dairy cattle throughout the world. Despite 35 years of research, the definitive etiologic agent associated with the disease process is still unknown. Previous studies have demonstrated that multiple bacterial species are associated with lesions, with spirochetes being the most reliably identified organism. This study details the deep sequencing-based metagenomic evaluation of 48 staged DD biopsy specimens collected during a 3-year longitudinal study of disease progression. Over 175 million sequences were evaluated by utilizing both shotgun and 16S metagenomic techniques. Based on the shotgun sequencing results, there was no evidence of a fungal or DNA viral etiology. The bacterial microbiota of biopsy specimens progresses through a systematic series of changes that correlate with the novel morphological lesion scoring system developed as part of this project. This scoring system was validated, as the microbiota of each stage was statistically significantly different from those of other stages (P < 0.001). The microbiota of control biopsy specimens were the most diverse and became less diverse as lesions developed. Although Treponema spp. predominated in the advanced lesions, they were in relatively low abundance in the newly described early lesions that are associated with the initiation of the disease process. The consortium of Treponema spp. identified at the onset of disease changes considerably as the lesions progress through the morphological stages identified. The results of this study support the hypothesis that DD is a polybacterial disease process and provide unique insights into the temporal changes in bacterial populations throughout lesion development.

The genetic architecture of complete blood counts in lactating Holstein dairy cows.

Complete blood counts (CBCs) measure the abundance of individual immune cells, red blood cells, and related measures such as platelets in circulating blood. These measures can indicate the health status of an animal; thus, baseline circulating levels in a healthy animal may be related to the productive life, resilience, and production efficiency of cattle. The objective of this study is to determine the heritability of CBC traits and identify genomic regions that are associated with CBC measurements in lactating Holstein dairy cattle. The heritability of CBCs was estimated using a Bayes C0 model. The study population consisted of 388 cows with genotypes at roughly 75,000 markers and 16 different CBC phenotypes taken at one to three time points (n = 33, 131, and 224 for 1, 2, and 3 time points, respectively). Heritabilities ranged from 0.00 ± 0.00 (red cell distribution width) to 0.68 ± 0.06 (lymphocytes). A total of 96 different 1-Mb windows were identified that explained more than 1% of the genetic variance for at least one CBC trait, with 10 windows explaining more than 1% of the genetic variance for two or more traits. Multiple genes in the identified regions have functions related to immune response, cell differentiation, anemia, and disease. Positional candidate genes include RAD52 motif-containing protein 1 (RDM1), which is correlated with the degree of immune infiltration of immune cells, and C-X-C motif chemokine ligand 12 (CXCL12), which is critically involved in neutrophil bone marrow storage and release regulation and enhances neutrophil migration. Since animal health directly impacts feed intake, understanding the genetics of CBCs may be useful in identifying more disease-resilient and feed-efficient dairy cattle. Identification of genes responsible for variation in CBCs will also help identify the variability in how dairy cattle defend against illness and injury.

Genomic characterization of highly pathogenic avian influenza A H5N1 virus newly emerged in dairy cattle.

In March 2024, the emergence of highly pathogenic avian influenza (HPAI) A (H5N1) infections in dairy cattle was detected in the United Sates for the first time. We genetically characterize HPAI viruses from dairy cattle showing an abrupt drop in milk production, as well as from two cats, six wild birds, and one skunk. They share nearly identical genome sequences, forming a new genotype B3.13 within the 2.3.4.4b clade. B3.13 viruses underwent two reassortment events since 2023 and exhibit critical mutations in HA, M1, and NS genes but lack critical mutations in PB2 and PB1 genes, which enhance virulence or adaptation to mammals. The PB2 E627 K mutation in a human case associated with cattle underscores the potential for rapid evolution post infection, highlighting the need for continued surveillance to monitor public health threats.

Influence of a sodium-saccharin sweetener on the rumen content and rumen epithelium microbiota in dairy cattle during heat stress.

The effect of a saccharin-based artificial sweetener was tested on animal performance measures and on the microbial communities associated with the rumen content and with the rumen epithelium during heat stress. Ten cannulated Holstein-Friesian milking dairy cattle were supplemented with 2 g of saccharin-based sweetener per day, top-dressed into individual feeders for a 7-day adaptation period followed by a 14-day heat stress period. A control group of ten additional cows subjected to the same environmental conditions but not supplemented with sweetener were included for comparison. 16S rRNA gene amplicon sequencing was performed on rumen content and rumen epithelium samples from all animals, and comparisons of rumen content microbiota and rumen epithelial microbiota were made between supplemented and control populations. Supplementation of the saccharin-based sweetener did not affect the rumen content microbiota, but differences in the rumen epithelial microbiota beta-diversity (PERMANOVA, P = 0.003, R2 = 0.12) and alpha-diversity (Chao species richness, P = 0.06 and Shannon diversity, P = 0.034) were detected between the supplemented and control experimental groups. Despite the changes detected in the microbial community, animal performance metrics including feed intake, milk yield, and short-chain fatty acid (acetic, propionic, and butyric acid) concentrations were not different between experimental groups. Thus, under the conditions applied, supplementation with a saccharin-based sweetener does not appear to affect animal performance under heat stress. Additionally, we detected differences in the rumen epithelial microbiota due to heat stress when comparing initial, prestressed microbial communities to the communities after heat stress. Importantly, the changes occurring in the rumen epithelial microbiota may have implications on barrier integrity, oxygen scavenging, and urease activity. This research adds insight into the impact of saccharin-based sweeteners on the rumen microbiota and the responsivity of the rumen epithelial microbiota to different stimuli, providing novel hypotheses for future research.

Mitigating the effects of heat stress is becoming more and more important with global increases in temperatures. Heat stress negatively affects livestock health and performance. One way to mitigate the effects of heat stress on livestock is to increase feed intake during stress conditions by enhancing palatability of the feed by adding artificial sweeteners. In this study, we investigated whether supplementation of the diet with a saccharin-based sweetener affected dairy cattle performance and the rumen microbial communities during heat stress. We show that supplementation with a saccharin-based artificial sweetener did not affect the performance of the dairy cattle during heat stress. However, the sweetener resulted in changes in the rumen microbial communities, particularly of the microbial communities attached to the rumen wall. These changes in the rumen wall microbial communities could potentially have implications for the host animal, for example in the integrity of the rumen wall barrier function. Future research will be needed to better understand the role of artificial sweeteners in potentially mitigating stress conditions for livestock and to understand their potential effects on microbial communities.

Pharmacokinetics, Milk Residues, and Toxicological Evaluation of a Single High Dose of Meloxicam Administered at 30 mg/kg per os to Lactating Dairy Cattle.

Adverse effects associated with overdose of NSAIDs are rarely reported in cattle, and the risk level is unknown. If high doses of NSAIDs can be safely administered to cattle, this may provide a longer duration of analgesia than using current doses where repeated administration is not practical. Meloxicam was administered to 5 mid-lactation Holstein dairy cows orally at 30 mg/kg, which is 30 times higher than the recommended 1 mg/kg oral dose. Plasma and milk meloxicam concentrations were determined using high-pressure liquid chromatography with mass spectroscopy (HPLC-MS). Pharmacokinetic analysis was performed by using noncompartmental analysis. The geometric mean maximum plasma concentration (Cmax) was 91.06 µg/mL at 19.71 h (Tmax), and the terminal elimination half-life (T1/2) was 13.79 h. The geometric mean maximum milk concentration was 33.43 µg/mL at 23.74 h, with a terminal elimination half-life of 12.23 h. A thorough investigation into the potential adverse effects of a meloxicam overdose was performed, with no significant abnormalities reported. The cows were humanely euthanized at 10 d after the treatment, and no gross or histologic lesions were identified. As expected, significantly higher plasma and milk concentrations were attained after the administration of 30 mg/kg meloxicam with similar half-lives to previously published reports. However, no identifiable adverse effects were observed with a drug dose 30 times greater than the industry uses within 10 days of treatment. More research is needed to determine the tissue withdrawal period, safety, and efficacy of meloxicam after a dose of this magnitude in dairy cattle.

Plasma Pharmacokinetics of Cannabidiol Following Oral Administration of Cannabidiol Oil to Dairy Calves.

Cannabidiol (CBD), the non-psychotropic component of cannabis, has drawn increased interest amongst some medical professionals for its potential therapeutic effects. Human and canine work has been done to describe CBD where it is already widely used, however, little is known about the effects of CBD in livestock species. The purpose of this descriptive study was to determine the pharmacokinetics (PK) of CBD in calves after a single oral exposure to CBD oil. Seven male Holstein calves received a single oral dose of 25 mg/mL CBD oil to achieve 5 mg/kg dose of CBD. Blood samples were collected for 48 (h) after dosing. The CBD geometric mean maximum concentration of 0.05 ug/mL was reached 7.5 h after administration. The geometric mean half-life was 23.02 h. Cannabidiol administered orally to cattle is slowly absorbed and has an extended elimination half-life compared to other species.

Salmonella enterica serovar Brandenburg abortions in dairy cattle.

Two separate late-term abortion outbreaks in Jersey heifers in July 2020 and December 2020 were investigated by the Iowa State University Veterinary Diagnostic Laboratory. We evaluated 3 whole fetuses and 11 sets of fresh and formalin-fixed fetal tissues during the course of the outbreaks. The late-term abortions were first identified at a heifer development site and subsequently observed at the dairy farm. Aborted fetuses had moderate-to-marked postmortem autolysis with no gross lesions identified. Observed clinical signs in cows at the dairy farm ranged from intermittent loose stools to acute post-abortion pyrexia and reduced feed intake. Routine histopathology and reproductive bacterial culture revealed acute, suppurative placentitis with moderate-to-heavy growth of Salmonella spp. group B from stomach contents, liver, placenta, and heifer fecal contents. Serotyping identified Salmonella enterica subsp. enterica serovar Brandenburg in all 14 fresh tissue cases, as well as individual and pooled heifer feces. Whole-genome sequencing analysis revealed that all isolates belonged to ST type 873 and possessed typhoid toxin genes, several fimbrial gene clusters, type III secretion system genes, and several pathogenicity islands. Abortions caused by Salmonella Brandenburg have not been reported previously in dairy cattle in the United States, to our knowledge.

Evaluating Ruminal and Small Intestinal Morphology and Microbiota Composition of Calves Fed a Macleaya cordata Extract Preparation.

The objective was to determine the impact of feeding MCE on ruminal and intestinal morphology and microbiota composition of calves. A total of 10 male and 10 female crossbred (dairy × beef) calves (6 d of age) were assigned randomly to control (CTL; n = 10) or MCE-supplemented (TRT; n = 10) groups. The MCE was fed in the milk replacer and top-dressed on the calf starter during pre-weaning (6 to 49 d) and post-weaning (50 to 95 d) periods, respectively. Calves were slaughtered at 95 d to collect rumen and intestinal samples to determine volatile fatty acid (VFA) profile, mucosal morphology, and microbiota composition. The effects of MCE were analyzed by accounting for the sex and breed effects. Feeding MCE increased rumen papillae length (p = 0.010) and intestinal villus height: crypt depth (p < 0.030) compared to CTL but did not affect rumen VFA profile. The TRT had a negligible impact on microbial community composition in both the rumen and the jejunum. In conclusion, feeding MCE from birth through weaning can improve ruminal and small intestinal mucosa development of calves despite the negligible microbiota composition changes observed post-weaning.

Corrigendum: Comparative Pharmacokinetics of Meloxicam Between Healthy Post-partum vs. Mid-lactation Dairy Cattle.

[This corrects the article DOI: 10.3389/fvets.2020.00548.].

Comparative Pharmacokinetics of Meloxicam Between Healthy Post-partum vs. Mid-lactation Dairy Cattle.

Lactating dairy cattle are at risk for various painful conditions throughout their life, such as lameness, parturition, mastitis, and metabolic disorders. These conditions necessitate adequate methods of analgesia to address welfare concerns through efficacious pain mitigation. As no method of analgesia has been approved for lactating dairy cattle, to date, research is necessary to determine effective pain management strategies for dairy cattle. In both the European Union and Canada, meloxicam has been approved for use in lactating dairy cattle as a methodology for pain control. The objective of this study was to characterize the pharmacokinetics of meloxicam administered orally and intravenously to lactating dairy cattle in the post-partum vs. mid-lactation period. In this parallel study design, 12 healthy, lactating Holsteins were enrolled within 24 h of freshening and randomly allocated to intravenous (0.2 mg/kg) or oral (1.0 mg/kg) meloxicam administration treatment groups. They were matched based on parity to 12, healthy cows that were considered mid-lactation [>150 days-in-milk (DIM)] to receive the same treatment. Based on meloxicam formulation, sampling times varied and plasma was collection via jugular venipuncture for 6 days. Plasma drug concentrations were evaluated using liquid chromatography coupled with mass spectroscopy and pharmacokinetic properties were evaluated using non-compartmental (i.e., statistical moments) analysis. Results indicated a decreased systemic clearance of meloxicam in post-partum relative to mid-lactation cows, which resulted in a longer half-life and increased total exposure independent of mode of administration. These results suggest a need for dose adjustments based on stage in lactation and further assessment of the impact of days-in-milk on milk withholding period.

Lactation stage impacts the glycolytic function of bovine CD4+ T cells during ex vivo activation.

Dairy cattle undergo dynamic physiological changes over the course of a full lactation into the dry period, which impacts their immunocompetence. During activation, T cells undergo a characteristic rewiring to increase the uptake of glucose and metabolically reprogram to favor aerobic glycolysis over oxidative phosphorylation. To date it remains to be completely elucidated how the altered energetic demands associated with lactation in dairy cows impacts T cell metabolic reprogramming. Thus, in our ex vivo studies we have examined the influence of stage of lactation (early lactation into the dry period) on cellular metabolism in activated bovine CD4+ T cells. Results showed higher rates of glycolytic function in activated CD4+ T cells from late lactation and dry cows compared to cells from early and mid-lactation cows. Similarly, protein and mRNA expression of cytokines were higher in CD4+ T cells from dry cows than CD4+ T cells from lactating cows. The data suggest CD4+ T cells from lactating cows have an altered metabolic responsiveness that could impact the immunocompetence of these animals, particularly those in early lactation, and increase their susceptibility to infection.

Rapid Communication: Use of pressure mat gait analysis in measuring pain following normal parturition in dairy cows.

Research investigating the pain of normal parturition is lacking as there are few objective methods for measuring pain. The objective of this research was to describe the gait of cows following eutocia using pressure mat gait analysis; and if meloxicam alters the gait of cows. Twenty Holstein cows within 26 h of unassisted calving were enrolled into the study. Treatment groups included: 1) postpartum cows administered meloxicam (MEL; n = 10); and 2) postpartum cows administered placebo (PLBO; n = 10). Meloxicam was administered by oral bolus at 1 mg/kg within 26 h of calving. Placebo cows were given an oral bolus of dry whey powder within 26 h of calving. A commercially available floor mat-based pressure/force measurement system was used to compare ambulation between treatment groups. Cows were walked across the mat before treatment administration, and 2, 4, 6, 8, 12, 24, 48, and 72 h posttreatment. The percent of total force, percent total contact pressure, and percent total impulse of the rear limbs were calculated. Outcome measures were statistically analyzed using repeated measures, with the cow serving as the experimental unit. Cows in the MEL group placed 48.9% (95% CI: 47.4% to 50.5%) of total force on the rear limbs compared to 46.3% (95% CI: 44.7% to 47.9%) in PLBO cows (P = 0.02). Total impulse on their rear limbs for the MEL cows was 50.5% (95% CI: 48.6% to 52.4%) compared to 46.7% (95% CI: 44.8% to 48.7%) for the PLBO cows (P = 0.01). No differences in contact pressure of the rear limbs were observed (P = 0.27). The PLBO cows had a longer gait 101.3 cm (95% CI: 95.9% to 106.6 cm) vs. 90.8 cm (95% CI: 85.4% to 96.1 cm) (P = 0.03). These findings show meloxicam-treated cows have altered weight distribution to the rear limbs as measured by pressure mat gait analysis, suggesting meloxicam may effectively treat postpartum pain.

Tissue residue depletion and estimation of extralabel meat withdrawal intervals for tulathromycin in calves after pneumatic dart administration.

The objectives of this study were to evaluate the injection site pathology and determine tissue residue depletion of tulathromycin in calves following pneumatic dart administration and to calculate the associated extralabel withdrawal interval (WDI). Castrated male Holstein calves were injected with ~2.6 mg/kg tulathromycin via pneumatic dart administration. At 1 (n = 2), 6, 12, 18, and 24 d after drug injection (n = 3/time point), calves were euthanized, and muscle, liver, kidney, fat, and injection site samples were harvested and analyzed for tulathromycin concentrations using a LC-MS/MS method. Gross pathology and histopathology evaluations on the injection site samples were also performed. Pneumatic dart administration of tulathromycin caused severe localized lesions of hemorrhage and edema on days 1 and 6, as well as severe pathological reactions in the subcutaneous muscle on days 1, 6, and 12. Slight to moderate reactions were still observed in the majority of the skin or subcutaneous/muscle samples on day 24. Measured tulathromycin concentrations were converted to calculate the concentrations of the marker residue CP-60,300 by dividing a conversion factor of 1.4. The data were used to calculate extralabel WDIs based on the guidelines from U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA). The results showed that tulathromycin concentrations were the highest in the liver (4,877.84 ± 65.33 µg/kg), kidney (5,819.52 ± 1,087.00 µg/kg), muscle (1,717.04 ± 140.35 µg/kg), injection site (51,884.05 ± 7,529.34 µg/kg), and fat (161.69 ± 36.48 µg/kg) at 6, 1, 1, 1, and 1 d, respectively, after treatment. Tulathromycin concentrations remained above the limit of quantification of 5 µg/kg in all tissues at 24 d. The calculated WDIs based on kidney data were 26 d using EMA method, 36 d using FDA method based on CP-60,300 data, and 45 d using FDA method based on tulathromycin data. These results suggest that pneumatic dart administration of tulathromycin causes injection site reactions in calves and an extended WDI is needed. One limitation of this study was the small sample size of 3 that did not meet FDA guideline requirement. Therefore, the calculated WDIs should be considered as preliminary and additional studies that use a larger number of animals and directly measure the concentrations of the marker residue CP-60,300 are needed to make a more conclusive recommendation on the extralabel WDI.

Molecular epidemiology of coagulase-negative Staphylococcus species isolated at different lactation stages from dairy cattle in the United States.

BACKGROUND: Coagulase negative Staphylococcus (CNS) species are currently the most prevalent intra-mammary pathogens causing subclinical mastitis and occasional clinical mastitis or persistent infection in lactating dairy cattle. More than 10 CNS species have been identified, but they are generally managed as one group on most dairies in the United States. However, improved management decisions and treatment outcomes may be achieved with better understanding of the prevalent species, pathogenicity and strain diversity within and across dairies. METHODOLOGY: A total of 604 CNS isolates were cultured from milk samples collected during a dry-cow treatment clinical trial conducted on 6 dairy herds in 4 states in the US. All the study cows were randomized to receive 1 of the 3 different intra-mammary antimicrobial infusions (Quatermaster, Spectramast DC or ToMorrow Dry Cow) at dry-off. Milk samples were collected at dry-off, calving (0-6 days in milk, DIM), post-calving (7-13 DIM) and at mastitis events within the first 100 DIM. The CNS isolates were identified to species level by partial sequencing of the rpoß gene, and genetic relatedness within species was investigated by phylogenetic analysis of the pulse-field gel electrophoresis profiles of the isolates. RESULTS: The major CNS species identified were S. chromogenes (48.3%), S. haemolyticus (17.9%), S. simulans and S. epidermidis (each at 6.5%). Other CNS species identified at lower frequencies included S. hominis, S. auricularis, S. sciuri, S. spp KS-SP, S. capitis, S. cohnii, S. warneri, S. pasteuri, S. xylosus, S. hyicus, S. equorum, S. microti, S. rostri, S. gallinarum, S. saprophyticus and S. succinus. Phylogenetic analyses of the major species types demonstrated an association between genetic relatedness and epidemiological distributions of S. chromogenes, S. simulans, S. haemolyticus and S. auricularis. Additionally, identical strains of S. chromogenes and S. simulans were isolated from the same udder quarter of several cows at consecutive sample stages. The rest of the minor species had no deducible genetic-epidemiological link. DISCUSSION: The observed association between genetic and epidemiological distributions indicated animal-adapted nature of four CNS species, suggesting possible host-adapted and environmental transmission of these species. Multi-stage isolation of the same udder quarter strain was evidence for chronic intra-mammary infection. CONCLUSION: The different CNS species and strains circulating on US dairy herds were genetically diverse. Four species identified were likely udder-adapted pathogens, 2 of which caused persistent infection. Our findings are important in guiding the design of effective mastitis control strategies.