Antimicrobial Metaphylaxis and its Impact on Health, Performance, Antimicrobial Resistance, and Contextual Antimicrobial Use in High-Risk Beef Stocker Calves.

The objective of this blinded, cluster-randomized, complete block trial was to evaluate the impact of metaphylaxis on health, performance, antimicrobial resistance, and contextual antimicrobial use (AMU) in high-risk beef stocker calves. Calves (n = 155) were randomly assigned to receive either saline or tulathromycin at the time of arrival processing. Deep nasopharyngeal swabs were collected from each calf at arrival and 14 d later. Calves were monitored for bovine respiratory disease (BRD) for 42 d. Body weights were obtained at arrival, days 14, 28, and 42. Contextual antimicrobial use (AMU) was calculated using dose and mass-based metrics. Calves given tulathromycin had a greater average daily gain (0.96 ±â€…0.07 kg vs. 0.82 ±â€…0.07 kg; P = 0.034) and lower prevalence of BRD than controls (17% vs. 40%; P = 0.008). Proportions of calves with BRD pathogens identified at arrival were similar between treatment groups [17%; P = 0.94]. Proportions of calves with BRD pathogens identified at day 14 were lower for calves receiving tulathromycin compared to controls (15% vs. 60%, P < 0.001). Overall, 81% of Pastuerella multocida isolates and 47% of Mannheimia haemolytica isolates were pansusceptible. When measured as regimens per head in, AMU in calves receiving tulathromycin was higher than calves receiving saline (P = 0.01). Under the conditions of this study, metaphylaxis had positive impacts on the health and performance of high-risk beef stocker calves, did not contribute to the selection of resistant bacterial isolates in the nasopharynx of treated cattle, and increased AMU.

In this study, we investigated the impact of metaphyactic antimicrobial administration on health, performance, and antimicrobial use in high-risk beef stocker calves. Our findings demonstrated that metaphylaxis improves performance and has positive effects on animal health and well-being but increases total antimicrobial use. Additionally, our study revealed that metaphylaxis alone does not contribute to the selection of antimicrobial-resistant pathogens in the upper airway of treated cattle.

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.

Physical traits, performance data, and reproductive tract maturity score can be used to predict fertility and likelihood of early conception in beef replacement heifers consigned to a heifer development program in the southeastern United States.

OBJECTIVE: To identify growth and reproductive measurements that can be used to select heifers with the potential to be more reproductively efficient. SAMPLE: A total of 2,843 heifers consigned to the Georgia Heifer Evaluation and Reproductive Development program between 2012 and 2021 with a mean (min, max) age of heifers at delivery of 347 days (275, 404). PROCEDURES: Reproductive tract maturity score (RTMS), weight at delivery as a percentage of target breeding weight, hip height 3 to 4 weeks after delivery, and average daily gain during the first 3 to 4 weeks after delivery were evaluated as potential predictors of the variables of interest. RESULTS: The model-adjusted odds of pregnancy were 1.40 to 1.67 times higher for heifers with an RTMS of 3, 4, or 5 when compared to heifers with an RTMS of 1 or 2. For every 2.5-cm increase in hip height and every 1-month increase in age at the beginning of the breeding period the model-adjusted odds of pregnancy were 1.10 and 1.16 times higher, respectively. The model-adjusted pregnancy hazard rate for heifers with an RTMS of 3, 4, or 5 was 1.19 to 1.25 times higher than that of heifers with an RTMS of 1 or 2. For every 2.5-cm increase in hip height, the model-adjusted hazard rate for pregnancy was 1.04 times greater. CLINICAL RELEVANCE: Physical traits related to animal maturity and attainment of early puberty can be used to select heifers that are more likely to become pregnant early in their first breeding season.

Retrospective evaluation of the causes and distribution of lameness in beef and dairy cattle evaluated by ambulatory and in-house clinical services at a North American veterinary teaching hospital.

OBJECTIVE: To describe the causes and distribution of lameness in beef and dairy cattle presenting to either a primary care ambulatory or in-house clinical service at a veterinary teaching hospital. SAMPLE: This retrospective clinical case study was conducted by reviewing hospital admissions of beef and dairy cattle seen by in-house or ambulatory clinicians at a veterinary teaching hospital from 2001 to 2021. PROCEDURES: Final diagnosis was recorded and, when available, the affected limb, whether a lesion was localized to the digit, and the affected claw were also recorded. Data were stratified by location of initial evaluation (ambulatory vs in hospital), period of presentation, production class, age, sex, and whether the final diagnosis was infectious or noninfectious. RESULTS: Overall, 2,220 animals met criteria for inclusion in the study. The most common diagnoses were noninfectious in nature and affected a hind limb more often than a forelimb. More than 82% of all cattle had lameness localized to the digit, with the lateral claw being affected more than 80% of the time. CLINICAL RELEVANCE: Lameness is an important concern from both a humane and economic standpoint. The results of this study will help with the diagnosis and prevention of lameness in beef and dairy cattle of different ages and production classes.

Assessment of effectiveness of deworming options in recently weaned beef cattle utilizing different anthelmintic programs in the southeast.

This study evaluated the effects of three different anthelmintic strategies on animal performance and anthelmintic effectiveness in weaned calves during a 42-d preconditioning period. The study was conducted at four locations over 2 yr and included a total of 797 recently weaned spring-born calves (initial BW 260 ± 37.7 kg). At the start of each year, at each location, calves were weaned and randomly assigned to one of four treatments: 1) oxfendazole (ORAL); 2) transdermal eprinomectin (POUR); 3) both anthelmintic treatments (BOTH); and 4) the control (CONT) group who did not receive treatment. Anthelmintic was applied per the manufacturer recommendation, the transdermal eprinomectin was administered at 1 mL per 10 kg and oxfendazole was administered orally at 1 mL per 50 kg. Weights were measured at the start of the study (day 0) and again at the end of the preconditioning phase (day 42). Fecal samples were collected at the start of the study prior to treatment application (day 0) and again on day 14. Rumen fluid was collected at the start of the study prior to treatment (day 0) and again on day 6. There were treatment effects for all performance metrics (P < 0.001). All treatments had greater weight gain and value of weight gained (P < 0.024), and all three strategies did not differ from each other (P > 0.420). On day 0, there were no (P = 0.795) treatment effects detected for fecal eggs per gram (EPG) counts. On day 14, there were (P < 0.001) treatment effects for EPG counts with feces from CONT calves containing greater (P < 0.014) EPG than feces from treated calves. EPG in feces from BOTH calves did not differ (P > 0.123) from the other two treated groups and feces from POUR calves tended (P = 0.052) to contain greater EPG counts than feces from ORAL calves. Volatile fatty acids were similar across treatments on days 0 and 6 (P > 0.115). Butyrate tended (P = 0.063) to be lower in ORAL on day 6. These results suggest that using eprinomectin and oxfendazole in combination was an effective strategy for reducing EPG and improving performance during a 42-d preconditioning phase.

High-Risk Cattle Management and Stocker Calf Health: Modulation of the Bovine Respiratory Microbiome from a Systems Perspective.

Bovine respiratory disease (BRD) affects animals in all segments of the North American beef industry. The segmented nature of the beef industry results in the marketing of cattle that are considered to be at high risk of developing BRD. The microbiota is the complex microbial ecosystem that exists in and on the body of all animals. The respiratory tract has its unique microbiota that is shaped by many factors. Stress reduction, appropriate nutritional management, strategic use of vaccines, and antimicrobial administration targeted to the highest risk individuals have the potential to stabilize an inherently unstable microbial population and enhance calf health.

Antimicrobial resistance in Mannheimia haemolytica: prevalence and impact.

Bovine respiratory disease (BRD) is the most common cause of morbidity and mortality in North American beef cattle. In recent years, isolation of strains of Mannheimia haemolytica that are resistant to multiple different classes of antimicrobials has become commonplace. New research would suggest that the routine use of antimicrobials by some cattle operations might be driving emerging resistance patterns, with the majority of the spread observed due to propagation of strains of M. haemolytica that have acquired integrative conjugative elements. To date, there is little information evaluating the impact of antimicrobial resistance on clinical outcome in cattle with BRD.

Concordance of disk diffusion, broth microdilution, and whole-genome sequencing for determination of in vitro antimicrobial susceptibility of Mannheimia haemolytica.

BACKGROUND: Extensive drug resistance (XDR) is an emerging concern with Mannheimia haemolytica, and a variety of testing methods are available for characterizing in vitro antimicrobial susceptibility. OBJECTIVES: To compare the concordance among disk diffusion, broth microdilution, and whole genome sequencing (WGS) for susceptibility testing of M. haemolytica before and after mass treatment using tulathromycin. ANIMALS: Forty-eight M. haemolytica isolates collected from high-risk beef stocker calves before and after mass treatment (metaphylaxis) using tulathromycin (Draxxin, Zoetis, Parsippany, NJ) given at the label dosage of 2.5 mg/kg body weight SC in the neck. METHODS: In vitro antimicrobial susceptibility was determined for all 48 isolates using disk diffusion, broth microdilution, and WGS. Concordance was calculated between pairs of susceptibility testing methods as follows: number of isolates classified identically by the 2 testing methods for each timepoint, divided by the number of isolates tested at that timepoint. Discordance was calculated as follows: number of isolates classified differently by the 2 testing methods for each timepoint, divided by the number of isolates tested at that timepoint. RESULTS: Concordance between testing methods ranged from 42.3% to 100%, depending on antimicrobial evaluated, timing of sample collection, and testing method used. Very major errors were identified in up to 7.7% of classifications whereas minor errors were seen in up to 50% of classifications depending on antimicrobial evaluated, timing of sample collection, and testing method used. CONCLUSIONS AND CLINICAL IMPORTANCE: Our results show that discrepancies in the results of different susceptibility testing methods occur and suggest a need for greater harmonization of susceptibility testing methods.

Mannheimia haemolytica and Pasteurella multocida in Bovine Respiratory Disease: How Are They Changing in Response to Efforts to Control Them?

The bacteria Mannheimia haemolytica and Pasteurella multocida contribute to bovine respiratory disease (BRD), which is often managed with antimicrobials. Antimicrobial resistance in these bacteria has been rare, but extensively drug-resistant strains have recently become common. Routine antimicrobial use may be driving this resistance. Resistance spread is caused in part by propagation of strains harboring integrative conjugative elements. The impact of antimicrobial resistance on treatment outcomes is not clear, but clinical observations suggest that response to first treatment has decreased over time, possibly because of resistance. Clinicians should consider antimicrobial resistance when designing BRD treatment and control programs.

Genetic characterization of susceptible and multi-drug resistant Mannheimia haemolytica isolated from high-risk stocker calves prior to and after antimicrobial metaphylaxis.

Bovine Respiratory Disease (BRD) is a major threat to animal health and welfare in the cattle industry. Strains of Mannheimia haemolytica (Mh) that are resistant to multiple classes of antimicrobials are becoming a major concern in the beef industry, as the frequency of isolation of these strains has been increasing. Mobile genetic elements, such as integrative conjugative elements (ICE), are frequently implicated in this rapid increase in multi-drug resistance. The objectives of the current study were to determine the genetic relationship between the isolates collected at arrival before metaphylaxis and at revaccination after metaphylaxis, to identify which resistance genes might be present in these isolates, and to determine if they were carried on an ICE. Twenty calves culture positive for Mh at arrival and revaccination were identified, and a total of 48 isolates with unique susceptibility profiles (26 from arrival, and 22 from revaccination) were submitted for whole-genome sequencing (WGS). A phylogenetic tree was constructed, showing the arrival isolates falling into four clades, and all revaccination isolates within one clade. All revaccination isolates, and one arrival isolate, were positive for the presence of an ICE. Three different ICEs with resistance gene modules were identified. The resistance genes aphA1, strA, strB, sul2, floR, erm42, tetH/R, aadB, aadA25, blaOXA-2, msrE, mphE were all located within an ICE. The gene bla-ROB1 was also present in the isolates, but was not located within an ICE.

Characterization and comparison of cell-mediated immune responses following ex vivo stimulation with viral and bacterial respiratory pathogens in stressed and unstressed beef calves1.

The goal of this study was to compare the cell-mediated immune responses of highly commingled, sale-barn origin calves (STR; n = 10) to those of single source calves that had been weaned for 60 d (UNS; n = 10). Peripheral blood mononuclear cells and neutrophils (PMNs) were isolated from jugular venous blood of each calf. Peripheral blood mononuclear cells were stimulated with Concanavalin A (ConA), BVDV-1, BVDV-2, BHV-1, Mannheimia haemolytica, and Pasteurella multocida and evaluated for clonal proliferation and secretion of IL-8 into cell culture supernatants. The native functional capacities of PMNs were evaluated in response to stimulation with heat-killed Escherichia coli and Staphylococcus aureus. Complete blood counts and serum biochemical profiles were performed for each animal at the time of sample collection. Compared with STR calves, UNS calves had greater lymphocyte proliferative responses following stimulation BVDV1 (P = 0.041), BVDV2 (P = 0.002), BHV-1 (P = 0.001), M. haemolytica (P = 0.016), and P. multocida (P = 0.049). In addition, PMNs isolated from UNS calves had a greater ability to phagocytose E. coli (P = 0.001) and S. aureus (P = 0.003) when compared with STR calves. Serum nonesterified fatty acids were higher in STR calves (P < 0.001). Serum ß-hydroxybutyrate was lower in STR calves (P < 0.003). These data suggest that immunologic and physiologic differences exist between STR and UNS calves. Although the underlying mechanisms for these differences are not clear, it is possible that combinations of energy imbalances, stress-induced immunosuppression, and general immune naiveté may predispose STR calves to an increased risk of morbidity and mortality due to bovine respiratory disease.

Diagnosis and Treatment of Clinical Rumen Acidosis.

Clinical rumen acidosis is an important cause of morbidity and mortality in both large and small ruminants. Feeding and management practices that lead to the consumption of large amounts of readily fermentable carbohydrates precipitate clinical disease. The fermentation of carbohydrates into volatile fatty acids and lactate causes acidosis (local and systemic), rumen ulceration, cardiovascular compromise, and organ dysfunction. Animals affected with acidosis can suffer from numerous sequelae. Treatment of animals with clinical rumen acidosis is focused on addressing plasma volume deficits, correcting acid-base disturbances, and restoring a normal rumen microenvironment.

Expression of inflammation-associated genes in circulating leukocytes and activity of indoleamine-2,3-dioxygenase in dairy cattle with acute puerperal metritis and bacteremia.

OBJECTIVE: To investigate whether expression of genes associated with inflammation and activity of indoleamine-2,3-dioxygenase (IDO) correlated with disease status and prevalence of bacteremia in post-partum dairy cattle with and without acute puerperal metritis (APM). PROCEDURES: Blood was collected from cattle with APM and control cattle matched by parity and days in milk. Leukocytes were isolated and expression of 6 genes was quantified. Activity of IDO was measured in serum with higher performance liquid chromatography (HPLC). RESULTS: The relative expression of IL-1ß in cattle with APM was significantly lower than that in controls. IDO activity was not significantly different between bacteremic and non-bacteremic cattle CONCLUSIONS AND CLINICAL RELEVANCE: The expression of IL-1ß was lower in cattle with APM. The lower levels of IL-1ß expression in PBMCs of cattle with APM suggest impaired inflammatory responses and may contribute to the development of the disease in this population of animals.

Retrospective Comparison of Gastrosplenic Entrapment of the Small Intestine to Other Strangulating Small Intestinal Lesions in Adult Horses.

OBJECTIVE: To compare clinical data of horses with entrapment of the small intestine by the gastrosplenic ligament (ESIGL) to clinical data of horses with other strangulating small intestinal lesions. STUDY DESIGN: Retrospective case series. METHODS: Medical records (January 2001-December 2011) of horses that had exploratory celiotomy for acute abdominal pain associated with strangulating small intestinal lesions were reviewed. Signalment, physical examination findings, clinicopathologic variables, surgical findings and surgical procedures performed, postoperative data and short-term survival were recorded. RESULTS: Clinical findings included excessive nasogastric reflux and abnormal abdominal fluid. Horses with ESIGL were significantly more likely to require intestinal resection and anastomosis and produced significantly less reflux postoperatively than horses with other strangulating small intestinal obstructions. Geldings were significantly more likely to develop ESIGL than mares or stallions. Quarter Horse or Quarter Horse type breeds were predisposed to ESIGL. Survival to hospital discharge in horses with ESIGL (16/22; 72.7%) was significantly higher than that of horses with other strangulating small intestinal obstructions (92/183; 50%). CONCLUSIONS: ESIGL was more prevalent in this population of horses evaluated for acute abdominal pain than in previous studies, accounting for 10.7% of all horses with strangulating small intestinal lesions. Geldings and Quarter Horse or Quarter Horse related breeds are predisposed to this condition. The prognosis for survival to hospital discharge was fair to good.

Multicenter case-control study of signalment, diagnostic features, and outcome associated with cervical vertebral malformation-malarticulation in horses.

OBJECTIVE: To compare signalment of horses with cervical vertebral malformation-malarticulation (CVM) with that of control horses and to describe results of clinical examination, diagnostic imaging and necropsy findings, and reported outcome in horses with CVM. DESIGN: Retrospective case-control study. ANIMALS: 270 horses with CVM and 608 control horses admitted to 6 veterinary hospitals from 1992 through 2007. PROCEDURES: Medical records of participating hospitals were reviewed to identify horses with CVM (ie, case horses) and contemporaneous control (non-CVM-affected) horses that were admitted for treatment. Signalment was compared between case horses and control horses. Results of clinical examination, laboratory and diagnostic imaging findings, necropsy results, and outcome were assessed for horses with CVM. RESULTS: Case horses were younger (median age, 2 years) than were control horses (median age, 7 years). Thoroughbreds, warmbloods, and Tennessee Walking Horses were overrepresented in the CVM group. Gait asymmetry and cervical hyperesthesia were frequently detected in horses with CVM. Vertebral canal stenosis and articular process osteophytosis were commonly observed at necropsy; agreement between the results of radiographic or myelographic analysis and detection of lesions at necropsy was 65% to 71% and 67% to 78%, respectively. Of 263 horses with CVM for which outcome was recorded, 1 died and 172 (65.4%) were euthanatized. CONCLUSIONS AND CLINICAL RELEVANCE: Odds of a diagnosis of CVM were greater in young horses and horses of specific breeds. Detection of gait asymmetry and cervical hyperesthesia were frequently reported in association with CVM. Accurate diagnosis of lesions associated with CVM by use of radiography and myelography can be challenging.