Clinical disease and lung lesions in calves experimentally inoculated with Histophilus somni five days after metaphylactic administration of tildipirosin or tulathromycin

Strategies for Bovine Respiratory Disease (BRD) Diagnosis and Prognosis: A Comprehensive Overview

Despite significant advances in vaccination strategies and antibiotic therapy, bovine respiratory disease (BRD) continues to be the leading disease affecting the global cattle industry. The etiology of BRD is complex, often involving multiple microbial agents, which lead to intricate interactions between the host immune system and pathogens during various beef production stages. These interactions present environmental, social, and geographical challenges. Accurate diagnosis is essential for effective disease management. Nevertheless, correct identification of BRD cases remains a daunting challenge for animal health technicians in feedlots. In response to current regulations, there is a growing interest in refining clinical diagnoses of BRD to curb the overuse of antimicrobials. This shift marks a pivotal first step toward establishing a structured diagnostic framework for this disease. This review article provides an update on recent developments and future perspectives in clinical diagnostics and prognostic techniques for BRD, assessing their benefits and limitations. The methods discussed include the evaluation of clinical signs and animal behavior, biomarker analysis, molecular diagnostics, ultrasound imaging, and prognostic modeling. While some techniques show promise as standalone diagnostics, it is likely that a multifaceted approach-leveraging a combination of these methods-will yield the most accurate diagnosis of BRD.

Pharmacokinetics and bioavailability of tildipirosin following intravenous and subcutaneous administration in horses

This study was designed to investigate the safety and pharmacokinetic (PK) profile of tildipirosin in horses after intravenous (i.v.) and subcutaneous (s.c.) injection of a single dose at 4 mg/kg of body weight (b.w.). A total of 12 healthy mixed breed horses were used in the study. Horses were monitored for systemic and local adverse effects, and whole blood samples were collected for hematology and plasma biochemistry analysis at time (0) and at 6, 24, and 72 h after drug administration. For PK analysis, blood samples were collected at pre-determined times before and after tildipirosin administration. Plasma concentrations of tildipirosin were determined using ultra-high-performance liquid chromatography-ultraviolet detection method (UHPLC-UV). All horses tolerated the i.v. injection of tildipirosin without showing any systemic adverse effects. However, a non-painful, soft swelling appeared at the s.c. injection site in 5 horses (41.7%). On average, tildipirosin reached a maximum plasma concentration (C_max ) of 1257 ng/ml (geometric mean) between 0.5 and 1.5 h after s.c. administration (T_max ). The geometric mean values for total body clearance (Cl), the apparent volume of distribution based on the terminal phase (V_z ), and the apparent volume of distribution at steady-state (V_ss ) were 0.52 L/kg·h, 22 L/kg, and 10.0 L/kg, respectively. Data collected in this study suggests that tildipirosin can be used safely in horses with caution.

The Effect of Metaphylactic Use of Tildipirosin for the Control of Respiratory Disease in Long-Distance Transported Dairy Calves

The objective of this study was to evaluate the efficacy of two metaphylactic strategies using tildipirosin for the control of bovine respiratory disease (BRD) in dairy calves transported to a heifer raising facility within their first week of life. A total of 2,100 calves were enrolled in the study. Animals were transported for ~1,715 km, from dairies located in Minnesota to a calf raising facility located in New Mexico, where they were housed in individual hutches until weaning. Three days after arrival, calves were randomly allocated into three groups: (1) META1: single subcutaneous (SQ) injection of tildipirosin (Zuprevo™, Merck Animal Health) at enrollment at 4 mg/kg; (2) META2: SQ injection of tildipirosin at enrollment and 17 days later; (3) CON: untreated controls. The BRD incidence was 11.4, 10.8, and 9.4% for calves enrolled in the CON, META1, and META2, respectively (P = 0.44). Lung lesions diagnosed through ultrasonography was found in 21.0, 21.0, and 21.8% of calves enrolled in CON, META1, and META2, respectively (P = 0.99). Mortality tended to be greater for CON calves in comparison to META2 calves (1.5 vs. 0.6%, P = 0.06), but did not differ between calves enrolled in CON and META1 groups (1.5 vs. 1.2%, P = 0.55). Growth was not affected by metaphylaxis. The average daily gain for calves enrolled in CON, META1, and META2 was 517, 518 and 525 g, respectively (P = 0.25). Blood analysis revealed that some of the markers of inflammation assessed were influenced by metaphylaxis. At 27 days after enrollment, META2 calves had decreased concentrations of haptoglobin, serum amyloid A, and aspartate aminotransferase, compared to CON calves (P < 0.05). Additionally, CON calves had increased concentrations of globulins and lower albumin to globulin ratio than META2 calves at the end of the weaning period (P < 0.05). In conclusion, tildipirosin metaphylaxis did not decrease the incidence of BRD nor did it have an impact on weight gain. However, metaphylaxis with two injections of tildipirosin at enrollment and 17 days later tended to reduce mortality and improved the systemic inflammatory status of calves during the preweaning period.

Pharmacokinetics and bioavailability of tildipirosin following intravenous and subcutaneous administration in sheep

Tildipirosin is a semi-synthetic macrolide antibiotic commonly used in cattle and swine to treat bacterial pneumonia. The objective of this study was to investigate the pharmacokinetic profile of tildipirosin after a single intravenous (i.v.) and subcutaneous (s.c.) administration in healthy lambs. Eighteen lambs were randomly divided into three groups (n = 6 each). Lambs received a single s.c. dose of tildipirosin at 4 and 6 mg/kg b.w. in group 1 and 2, respectively. Lambs in group 3 received a single i.v. dose of tildipirosin at 4 mg/kg b.w. Blood samples were collected at 0, 0.5, 0.75, 1.5, 2, 3, 4, 6, 8, 10, 24, 36, 48 hr, and every 24 hr to day 21, and thereafter at day 28 posttildipirosin administration. The plasma concentrations of tildipirosin were determined using high-performance liquid chromatography with tandem mass spectrometry detection (LC⁄MS⁄MS). All lambs appeared to tolerate both the intravenous and subcutaneous injection of tildipirosin. Following i.v. administration, the elimination half-life (T_1/2 ), mean residence time (MRT), volume of distribution (Vd/F), and total body clearance (Cl/F) were 119.6 ± 9.0 hr, 281.9 ± 25.7 hr, 521.1 ± 107.2 L, and 2.9 ± 0.5 L/hr, respectively. No significant differences in C_max (657.0 ± 142.8 and 754.6 ± 227.1 ng/ml), T_max (1.21 ± 0.38 and 1.35 ± 0.44 hr), T_1/2 (144 ± 17.5, 156.5 ± 33.4 hr), and MRT (262.0 ± 30.2 and 250.6 ± 54.5 hr) were found in tildipirosin after s.c. dosing at 4 and 6 mg/kg b.w., respectively. The absolute bioavailability (F) of tildipirosin was 71.5% and 75.3% after s.c. administration of 4 and 6 mg/kg b.w., respectively. In conclusion, tildipirosin was rapidly absorbed and slowly eliminated after a single s.c. administration in healthy lambs. Tildipirosin could be used for the treatment and prevention of respiratory bacterial infections in sheep. However, further in vitro and in vivo studies to determine the efficacy and safety are warranted. To our knowledge, this is the first study to determine the tildipirosin pharmacokinetic parameters in sheep plasma.

Performance of multiple diagnostic methods in assessing the progression of bovine respiratory disease in calves challenged with infectious bovine rhinotracheitis virus and Mannheimia haemolytica1

The objective of this study was to evaluate the diagnostic performance of chute-side diagnostic methods for detecting physiological and pathological changes as indicators of early bovine respiratory disease (BRD) in calves experimentally inoculated with infectious bovine rhinotracheitis virus (IBR) and Mannheimia haemolytica (Mh). A challenge study was performed over 14 d in 30 Holstein steers [average weight (±SEM) = 211 kilograms (kg) ± 2.4 kg] inoculated on day 0 with IBR and on day 6 with Mh. Diagnostic methods included clinical illness scores (CIS), lung auscultation using a computer-aided stethoscope (CAS), rectal temperature, facial thermography, pulse oximetry, and bilateral thoracic ultrasonography. Animals were randomized into 1 of 5 necropsy days (days 6, 7, 9, 11, and 13) when the percentage of lung consolidation was estimated. The effect of study day on the results of the diagnostic methods and associations between each diagnostic method's values with lung consolidation measured at necropsy were determined with mixed models. Values for all diagnostic methods differed significantly (P < 0.01) by day. During the IBR phase (days 0 to 6) calves had "normal" to "moderate" CIS, whereas during the Mh phase (days 6.5 to 13) scores were predominantly "severe" to "moribund." Similarly, CAS scores were "normal" and "mild acute" during the IBR phase and "mild acute" to "moderate acute" after the Mh challenge. Oxygen saturation did not differ significantly between days 0, 1, 2, 4, and 6; however, significantly decreased 12 h after inoculation with Mh (P < 0.05). Mean lung consolidation between animal's right and left side recorded by ultrasound was 0.13% (±0.07) before the inoculation with Mh. However, during the Mh phase, mean consolidation increased significantly over time (P < 0.05). The percentage of lung consolidation at necropsy ranged from 1.7% (±0.82) on day 6 to 55.4% (±7.49) on day 10. Clinical illness scores, rectal temperature, facial thermography, oxygen saturation, and ultrasonography were significantly associated (P < 0.05) with lung consolidation at necropsy. In addition, there was a significant trend (P = 0.07) between CAS and lung consolidation scores at necropsy. These chute-side diagnostic methods are useful for detecting disease progression on animals with early stages of BRD.

Pharmacokinetics and Pharmacodynamics of Tildipirosin Against Pasteurella multocida in a Murine Lung Infection Model

Tildipirosin, a 16-membered-ring macrolide antimicrobial, has recently been approved for the treatment of swine respiratory disease and bovine respiratory disease. This macrolide is extensively distributed to the site of respiratory infection followed by slow elimination. Clinical efficacy has been demonstrated in cattle and swine clinical field trials. However, the pharmacokinetic/pharmacodynamic (PK/PD) index that best correlates with the efficacy of tildipirosin remains undefined. The objective of this study was to develop a PK/PD model following subcutaneous injection of tildipirosin against Pasteurella multocida in a murine lung infection model. The PK studies of unbound (f) tildipirosin in plasma were determined following subcutaneous injection of single doses of 1, 2, 4, 6, and 8 mg/kg of body weight in neutropenic lung-infected mice. The PD studies were conducted over 24 h based on twenty intermittent dosing regimens, of which total daily dose ranged from 1 to 32 mg/kg and dosage intervals included 6, 8, 12, and 24 h. The minimum inhibitory concentration (MIC) of tildipirosin against P. multocida was determined in serum. The inhibitory effect I_max model was employed for PK/PD modeling. The area under the unbound concentration-time profile over 24 h to MIC (fAUC_{0-24 h}/MIC) was the PK/PD index that best described the antibacterial activity in the murine infection model. The fAUC_{0-24 h}/MIC targets required to achieve the bacteriostatic action, a 1-log₁₀ kill and 2-log₁₀ kill of bacterial counts were 19.93, 31.89, and 53.27 h, respectively. These results can facilitate efforts to define more rational designs of dosage regimens of tildipirosin using classical PK/PD concepts for the treatment of respiratory diseases in pigs and cattle.

Case Study: Control of respiratory disease in male Holstein calves with tildipirosin and effect on health and growth from 0 to 4 months of age

In trial 1, phase 1, 48 male Holstein calves initially 2 to 4 d of age were transported 3.5 h to the research facility. Calves were randomly selected to either receive a s.c. injection of Zuprevo (Merck Animal Health, Summit, NJ; 4 mg of tildipirosin/kg of BW; TIL) the day after arrival (d 0) and again at weaning (d 42) or receive no injections (CON). Calves were fed 0.66 kg of milk replacer DM daily for 39 d and then 0.33 kg daily for 3 d. A starter was fed free choice for the 56 d of phase 1. In trial 1, phase 2, the same calves from phase 1 grouped by CON and TIL were moved to group pens (4 pens per treatment, 4 calves per pen) for the next 56 d. The starter was blended with 5% chopped grass hay and fed free choice. Trial 2 was similar to trial 1, phase 2 and used 48 two-month-old male Holstein calves. Calves were randomly selected to receive either a s.c. injection of Zuprevo (4 mg of tildipirosin/kg of BW; TIL) on d 0 or no injections (CON). In trial 1, phase 1, preweaning ADG and BCS change; postweaning starter intake and hip width change; overall starter intake, ADG, and hip width change; final hip width; and final BCS were greater for TIL than CON. During phase 2 of trial 1 and trial 2, calf ADG and hip width change were greater for TIL than CON. Overall, in transported Holstein calves, TIL improved ADG and structural growth by approximately 13%.