No abstract

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.

Needle-free injection was superior to needle injection for the control of iatrogenic transmission of A marginale.

Chemosterilization is reported in cattle fed chlortetracycline hydrochloride (CTC) at dosages ranging from 1.1mg/kg for 120 days to 11 mg/kg for 30-60 days. The relationship between plasma CTC drug concentration and carrier clearance has not been described. Chronic carrier status was established in 21 steers with a Virginia isolate of Anaplasma marginale and confirmed by cELISA and an A. marginale-specific RT-PCR. Four negative, splenectomized steers served as active disease transmission sentinels. Steers were randomized to receive 4.4 mg/kg/day (LD); 11 mg/kg/day (MD); or 22 mg/kg/day (HD) of oral chlortetracycline; or placebo (CONTROL) for 80 days. The LD, MD and HD treatment groups consisted of 5 infected steers and 1 splenectomized steer; CONTROL group had six infected steers and 1 splenectomized steer. The daily treatments and ration were divided equally and fed twice daily. Blood samples were collected semi-weekly for determining plasma drug concentration by ultrahigh performance liquid chromatography-mass spectrometry/mass spectrometry method and assessment of disease status by both cELISA and RT-PCR. Mean (CV%) chlortetracycline plasma drug concentrations in the LD, MD, and HD groups were 85.3 (28%), 214.5 (32%) and 518.9 (40%)ng/mL during days 4 through 53 of treatment. A negative RT-PCR assay result was confirmed in all CTC-treated groups within 49 days of treatment; however, cELISA required an additional 49 to 88 days before similar results. Subinoculation of splenectomized steers confirmed chemosterilization. These results are important for influencing future chemosterilization strategies and impacting free trade policy among countries and regions of contrasting endemicity.