Objective-To develop a method for experimental induction of equine rhinitis A virus (ERAV) infection in equids and to determine the clinical characteristics of such infection. Animals-8 ponies (age, 8 to 12 months) seronegative for antibodies against ERAV. Procedures-Nebulization was used to administer ERAV (strain ERAV/ON/05; n = 4 ponies) or cell culture medium (control ponies; 4) into airways of ponies; 4 previously ERAV-inoculated ponies were reinoculated 1 year later. Physical examinations and pulmonary function testing were performed at various times for 21 days after ERAV or mock inoculation. Various types of samples were obtained for virus isolation, blood samples were obtained for serologic testing, and clinical scores were determined for various variables. Results-ERAV-inoculated ponies developed respiratory tract disease characterized by pyrexia, nasal discharge, adventitious lung sounds, and enlarged mandibular lymph nodes. Additionally, these animals had purulent mucus in lower airways up to the last evaluation time 21 days after inoculation (detected endoscopically). The virus was isolated from various samples obtained from lower and upper airways of ERAV-inoculated ponies up to 7 days after exposure; this time corresponded with an increase in serum titers of neutralizing antibodies against ERAV. None of the ponies developed clinical signs of disease after reinoculation 1 year later. Conclusions and Clinical Relevance-Results of this study indicated ERAV induced respiratory tract disease in seronegative ponies. However, ponies with neutralizing antibodies against ERAV did not develop clinical signs of disease when reinoculated with the virus. Therefore, immunization of ponies against ERAV could prevent respiratory tract disease attributable to that virus in such animals.

Objective-To determine effects of ambient temperature, relative humidity, wind speed, relative barometric pressure, and temperature-humidity index (THI) on nasal submucosal and rectal temperatures in cattle during extreme summer conditions. Animals-20 black crossbred beef heifers (mean body weight, 217.8 kg). Procedures-Nasal submucosal and rectal temperatures were monitored every 2 hours for 24 hours on 3 nonconsecutive days when ambient temperature was forecasted to exceed 32.2°C. Ambient temperature, relative humidity, wind speed, and relative barometric pressure were continuously monitored at a remote weather station located at the research facility. The THI was calculated and used in the livestock weather safety index (LWSI). Relationships between nasal submucosal or rectal temperature and weather variables were evaluated. Results-Nasal submucosal and rectal temperatures were related to all weather variables monitored. A positive relationship was determined for ambient temperature and THI with both nasal submucosal and rectal temperatures. A negative relationship was evident for nasal submucosal and rectal temperature with relative humidity, wind speed, and relative barometric pressure. Nasal submucosal and rectal temperatures increased with increasing severity of LWSI category. Conclusions and Clinical Relevance-Effects of environmental conditions on thermoregulation in calves exposed to extreme heat were detected. The positive relationship between nasal submucosal temperature and ambient temperature and THI raised concerns about the efficacy of intranasal administration of temperature-sensitive modified-live virus vaccines during periods of extreme heat. Environmental conditions must be considered when rectal temperature is used as a diagnostic tool for identifying morbid cattle.

Objective-To determine associations of blood analysis variables and orbit and nasal planum surface temperatures with the onset and severity of Mycoplasma bovis pneumonia in calves. Animals-28 healthy calves. Procedures-Calves were challenged with M bovis (n = 24) on day 0 or not challenged (4). Blood samples were obtained for cardiac troponin I, CBC, and serum biochemical analyses on various days. Orbit and nasal planum surface temperatures were determined with infrared thermography on various days. Calves were euthanized, gross necropsies were performed, heart and lung samples were collected for histologic evaluation, and microbial cultures of lung samples were performed on day 14. Pneumonia severity was categorized as mild (< 10% lung consolidation) or moderate (≥ 10% lung consolidation). Associations between measured variables and severity of pneumonia or sample collection day were determined. Results-Plasma cardiac troponin I concentration for the 28 calves was significantly higher on day 14 than it was on day 0 or 7 (least squares mean, 0.02, 0, and 0 ng/mL, respectively). No other variables changed significantly during the study. No substantial gross or histologic abnormalities were identified in cardiac muscle samples. Day 14 plasma fibrinogen concentration was significantly different between calves with mild pneumonia and those with moderate pneumonia (mean, 0.44 and 0.74 g/dL, respectively). Calves with moderate pneumonia had significantly lower least squares mean surface temperature of the dorsal aspect of the nasal planum (18.7°C) versus calves with mild pneumonia (22.9°C). Conclusions and Clinical Relevance-Results indicated the evaluated variables had low value for assessment of bovine respiratory disease complex in calves.

Objective—To evaluate the effect of ambient temperature on viral replication and serum antibody titers following administration of an intranasal modified-live infectious bovine rhinotracheitis (IBR)-parainfluenza-3 (PI3) virus vaccine to beef calves housed in high– (> 32°C) and moderate– (21°C) ambient temperature environments. Animals—28 calves (mean weight, 206.8 kg). Procedures—Calves were randomly allocated to 4 treatment groups (housed outdoors during high ambient temperature with [HAT; n = 10] or without [HAC; 4] vaccination or housed indoors in a moderate ambient temperature with [MAT; 10] or without [MAC; 4] vaccination). Rectal and nasal mucosal temperatures were recorded every 2 hours from 8 AM to 8 PM on days 0 (vaccination) and 1. Nasal swab specimens were obtained on days 0 through 7 for virus isolation. Serum samples were collected on days 0, 7, 14, and 28 for determination of antibody titers. Results—Mean rectal temperature did not differ among the treatment groups. Mean nasal temperature for the HAT group was significantly higher than that for the MAT group at 6, 24, 30, 32, and 38 hours after vaccination. Viable IBR virus was isolated from all vaccinated calves on days 1 through 6. Two weeks after vaccination, vaccinated calves had anti-IBR antibody titers that were significantly greater than those for unvaccinated calves. Mean anti-IBR antibody titers did not differ significantly between the HAT and MAT groups. Conclusions and Clinical Relevance—Results indicated that, following vaccination with an intranasal modified-live IBR-PI3 virus vaccine, IBR viral replication and serum antibody titers did not differ significantly between calves housed in high– and moderate–ambient temperature environments.