Respiratory responses of mature horses to intravenous lobeline bolus

The respiratory stimulant lobeline has been used in equine clinical practice to increase inspiratory and expiratory airflow rates at rest in order to facilitate investigation of both lower and upper airway function. Some of the responses to lobeline in the pony have been reported, but the detailed time course, effect of dose, possible side effects and reproducibility associated with lobeline administration have not been described in the horse. Respiratory airflow rates and oesophageal pressure were measured with a Fleisch No. 5 pneumotachometer and lightweight facemask and a microtip pressure transducer catheter, respectively. The output of the Fleisch pneumotachometer was calibrated for flow rates up to +/- 70 l/s. Seven mature horses with no clinical signs of respiratory disease were studied. Investigations were conducted to determine: (1) the responses to different doses of lobeline (0.15, 0.20, 0.25 and 0.30 mg/kg bwt) as a rapid i.v. bolus (6 horses); (2) arterial blood gases during and after lobeline administration (0.20 mg/kg bwt; 3 horses); and (3) the reproducibility of lobeline-stimulated hyperpnoea (5 horses; 2 doses of 0.20 mg/kg bwt lobeline, 15 min apart). All horses tolerated the lobeline-stimulated hyperpnoea well, although one always coughed or snorted at the onset. Mild tremor was noted following the highest dose in several horses. Apnoea of approximately 40 s was common after the hyperpnoea. Both tidal volume (VT) and frequency (fR) increased with lobeline dose. During peak hyperpnoea at a dose of 0.30 mg/kg bwt, peak inspired flow rate (PIF), peak expired flow rate (PEF) and minute ventilation (VE) were mean +/- s.e. 41+/-5 l/s, 61+/-10 l/s and 920+/-99 l/min, respectively. The hyperpnoea also caused marked changes in arterial PaO2, PaCO2 and pHa at 90 s after lobeline (0.20 mg/kg bwt) administration (mean +/- s.e. 146.0+/-6.9 mmHg, 20.6+/-0.8 mmHg and 7.707+/-0.020, respectively) compared to at rest (mean +/- s.e. 104.0+/-4.0 mmHg, 50.6+/-2.8 mmHg and 7.432+/-0.012). Dynamic lung compliance (Cdyn) was unaltered by lobeline administration. The lobeline-induced hyperpnoea was highly reproducible, with no significant difference in any of the parameters during 2 stimulations 15 min apart. Lobeline induced highly reproducible responses without any apparent adverse effects and may be useful in the investigation of pulmonary function in healthy horses and those with airway disease.     

Spirometric performance in Belgian Blue calves: II. Analysis of environmental factors and estimation of genetic parameters

Genetic parameters and environmental effects for spirometric variables (SV) in calves were estimated using 734 Belgian Blue calves (15 to 297 d of age), sired by 20 AI bulls. For each calf, the following SV were measured: 1) the average ventilation (l/min) recorded during the 15 s of maximal ventilatory changes induced by lobeline administration (0.25 mg/kg, i.v.) (15-s MV(L)); 2) the vital capacity, and the maximal peak expiratory and inspiratory flows recorded after lobeline administration; and 3) the ventilatory reserve (15-s MV(L) - ventilation at rest). Analysis of environmental factors showed age of calf, herd, sex, and vaccination status had significant effects on SV. A sire model and a multiple-trait derivative-free REML procedure were used to estimate genetic parameters for SV, body weight, and muscling score. Heritabilities for SV ranged from 0.28 +/- 0.11 to 0.44 +/- 0.16. Genetic correlations among SV varied from 0.76 to 0.98 and environmental correlations from 0.69 to 0.80. Genetic correlations of SV with body weight (0.25 to 0.56) and with muscling score (0.21 to 0.76) were positive, as were environmental correlations of SV with body weight (0.44 to 0.70) and muscling score (0.09 to 0.25). These results suggest that selection may improve SV without impairing other traits of economic importance.     

Spirometric Variables Recorded after Lobeline Administration in Healthy Friesian and Belgian White and Blue Calves: Normal Values and Effects of Somatic Growth

The purposes of the present study were: (1) to develop original equations to predict spirometric variables (SV) in healthy Friesian and Belgian White and Blue (BWB) calves < 1 year of age; and (2) to determine the effects of somatic growth on SV. Sixty-seven Friesian and 500 BWB calves were investigated. For each calf, the following SV were calculated: (1) the average minute volume derived using all the ventilatory cycles recorded during the 15 s of maximal ventilatory changes induced by lobeline administration (0.25 mg/kg, i.v.) (15-s LMV); (2) the maximal tidal volume, the maximal peak expiratory flow and the maximal peak inspiratory flow recorded from single breaths after lobeline administration (MVTL, MPEFLand MPIFL, respectively); (3) the ventilatory reserve (VRL= 15-s LMV - VEr; VEr= minute volume at rest). Mass specific (s) values were also calculated. All SV changed linearly with somatic growth in both Friesian and BWB calves. Since the rise in SV was more related to body weight than the age of calves, equations for reference values of SV always had body weight as the only independent variable. In the youngest calves, s SV were lower in the BWB breed. In the oldest calves (i.e. 1 year of age), s MPEFLand s MPIFLremained small in BWB calves whereas s MVTL, s 15-s LMV and s VRLwere almost equal in both breeds. These results could be related to the lower resistance to respiratory disorders in BWB calves < 1 year of age than in Friesian calves < 1 year of age.     

Interactions of cold stress and Pasteurella haemolytica in the pathogenesis of pneumonic pasteurellosis in calves: changes in pulmonary function

Thirteen healthy neonatal Holstein calves were cold stressed twice by hosing with cold water for 20 minutes, 12 hours between hosings. Measurements of the pattern of ventilation [tidal volume (VT), respiratory frequency (f), minute ventilation (VMIN), and functional residual capacity (FRC)], gas exchange properties of the lungs [alveolar ventilation (VA), oxygen uptake (VO2), CO2 production (VCO2), dead space ventilation (VD), dead space/tidal volume ratio (VD/VT), arterial oxygen tension (PaO2), arterial CO2 tension (PaCO2) and alveolar-arterial oxygen difference (AaDO2)] and of the mechanical properties of the pulmonary system [dynamic compliance (Cdyn), pulmonary resistance (RL), and total respiratory system resistance (RRS)] were taken. Calves responded to chilling by increasing VO2 and VCO2 necessitating an increase in VA. This was accomplished by increasing VT with reciprocal decreases in f so that VMIN remained constant. There was no change in Cdyn, RL, or AaDO2. Seven of these 13 calves were then exposed to intratracheal inoculation of 2 X 10(9) organisms of Pasteurella haemolytica, the remaining calves serving as controls. Within 1 hour, calves exposed to P haemolytica had increased VMIN, f, VD/VT, and VD. There was a decrease in PaO2 associated with increased AaDO2, but no change in PaCO2, Cdyn or RL. By 3 hours after inoculation, there were pronounced changes in PaO2 and AaDO2, and Cdyn was reduced below base-line values. By 12 hours after inoculation, calves infected with P haemolytica had increased RL and RRS and PaCO2, in addition to the previously mentioned changes. Data from Pasteurella-exposed calves indicate that gas exchange impairment and peripheral lung injury occur rapidly and that increases in airway resistance develop relatively late in the disease.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparative ventilation and gas exchange in the horse and the cow

Ventilation and gas exchange were studied in healthy, adult horses and cows, two large species with different lung structures and different breathing patterns. The oxygen uptake (VO2), carbon dioxide output (VCO2), respiratory rate (fR), minute ventilation (VE), alveolar ventilation (VA), alveolar oxygen pressure (PAO2), and VE/VO2 ratio were higher in the cows, while the tidal volume (VT) and physiological dead space (VD) were larger in the horses. The arterial blood gases, alveolar-arterial oxygen pressure difference (PAO2-PaO2) and VD/VT ratio did not differ between the two species. The higher VO2 in the cows was most likely due to the energy cost of standing, and possibly to a higher cost of digestion. The higher VE, VA, VE/VO2 and PAO2 were most likely secondary to the increased VO2 and the slightly higher respiratory exchange ratio (R) in the cows. In contrast to hypotheses based on allometric equations, the PAO2 of horses and cows did not appear to differ from that of smaller mammals. The VD was larger than that predicted from allometric equations, and even though the VD/VT ratio (0.50) was lower than the previously reported values for horses and cows, it was significantly larger than the predicted weight-independent value of 0.36. Re-examination of the data used to derive the equation for VD raised questions as to the validity of this equation, and it is suggested that caution be exercised in the use of allometric equations for prediction.     

Effects of frequency and airway pressure on gas exchange during interrupted high-frequency, positive-pressure ventilation in ponies

Cardiovascular effects and pulmonary gas exchange were compared during conventional mechanical ventilation (CMV) and interrupted high-frequency, positive-pressure ventilation (IHFPPV) in 6 anesthetized ponies in dorsal recumbency. When the peak airway pressure (Paw) was held constant at control values attained during CMV (18 to 20 cm of H2O), and the ventilator frequency of IHFPPV was varied over the range, 2.5 to 12.5 Hz, significant (P less than 0.05) changes from control values were observed only in the ratio of dead-space volume to tidal volume (VD/VT) and in the respiratory minute volume (VE). The mean (+/- SEM) carbon dioxide excretion (VCO2) was 2.12 +/- 0.1 ml/kg/min during IHFPPV. Dead-space ventilation ranged from 40 to 73.7% of total ventilation and increased directly with increasing frequency. The VE also increased, from 89 ml/kg/min at a ventilatory frequency of 2.5 Hz to 145 ml/kg/min at a frequency of 12.5 Hz. Maintaining the frequency of IHFPPV constant at 12.5 Hz and increasing the Paw over the range of 5 to 30 cm of H2O caused significant (P less than 0.05) changes in arterial partial pressure of O2 (PaO2), VCO2, pulmonary shunt fraction (QS/QT), VE, arterial-alveolar differences in oxygen tension (AaDO2), VD/VT, and cardiac output, compared with CMV. The PaO2 and the VCO2 increased linearly with increasing Paw. With increasing Paw, VD/VT decreased directly with increasing Paw from 98 to 69.3%. Gas exchange at a Paw of 15 cm of H2O during IHFPPV was equivalent to conditions at Paw of 20 cm of H2O during CMV. At a higher Paw during IHFPPV, improvements over control values were observed in gas exchange.     

Monthly, daily, and circadian variations of measurements of pulmonary mechanics in horses with chronic obstructive pulmonary disease

OBJECTIVES: To determine temporal variations of pulmonary function in horses without respiratory tract disease (controls) and horses with chronic obstructive pulmonary disease (COPD) and determine whether reversibility of airway obstruction after environmental control can be predicted by response to atropine administration. ANIMALS: 7 COPD-affected and 5 control horses. PROCEDURES: Pulmonary function testing was performed monthly during 3 consecutive months, daily for 5 consecutive days, and at 6-hour intervals for 24 hours before and after administration of atropine (0.02 mg/kg of body weight, i.v.) and after 5 consecutive months at pasture. Respiratory rate, tidal volume (VT), minute ventilation (VE), maximal change in transpulmonary pressure (deltaP(L)), pulmonary resistance (R(L)), and pulmonary elastance (E(L)) were calculated. RESULTS: COPD-affected horses had a significantly higher expiratory to inspiratory time ratio (T(E)/T(I)) and deltaP(L), E(L), and R(L) than horses without respiratory tract diseases during all periods and higher V(E) during monthly and daily evaluations. Daily variation in VT and monthly and circadian variation in E(L) were significant in COPD-affected horses. In control horses, significant changes were apparent only in T(E)/T(I) during daily recordings. In COPD-affected horses, reduction in deltaP(L), R(L), and E(L) was significant after atropine administration and after maintenance on pasture. CONCLUSIONS AND CLINICAL RELEVANCE: Despite variations in measurements of respiratory mechanics in both groups of horses, values remained significantly different between groups over time. Despite individual variation, measurements were repeatable during short and long periods. Response to administration of atropine to COPD-affected horses underestimated improvement in respiratory tract function that resulted from maintenance on pasture.     

Spirometric performance in Belgian Blue calves: I. Effects on economic losses due to the bovine respiratory disease complex

The aim of this study was to determine whether high spirometric performances in calves are associated with low economic losses due to the bovine respiratory disease complex (BRDC). Five spirometric variables (SV) were measured in 909 double-muscled Belgian Blue calves from 15 to 60 d of age. Afterward, calves were monitored for 6 mo to determine whether they developed BRDC and to determine the costs due to BRDC (i.e., medicine costs and veterinarians' fees, plus estimated financial losses due to mortality in case of death). To analyze the effects of spirometric performances on BRDC cost, a fixed linear model was used for each SV. In addition to SV, each model included the effects of sex, dam's parity, vaccination status, muscular development score, herd-period, and BW. Only herd-period and the maximal ventilation and the vital capacity had significant effects on costs due to BRDC, indicating that these two SV are major physiological determinants of economic losses associated with BRDC. Accordingly, it is assumed that an amelioration of maximal ventilation and vital capacity could result in increased resistance to BRDC in calves.     

Performance Evaluation of the ADS 1000 Ventilator Using a Lung Model

A laboratory evaluation was performed to evaluate the performance characteristics of a new veterinary ventilator. The ventilator studied was configured according to manufacturer's directions and attached to a test lung via a pneumotachograph and differential pressure transducer interfaced to a pulmonary mechanics analyzer system. Constant resistance (R=10 cm H₂O/L/sec) and compliance (C=3 ml/cm H₂O) factors were maintained for all trials. The ventilator operated at the manufacturer's preprogrammed parameters. In the first trial, body weight was the only variable. In the second trial, an endotracheal tube was placed in series between the ventilator's breathing circuit and the pneumotachograph. Body weights from 1–20 kgs were evaluated. Mean values for respiratory rate (RR), minute ventilation (VE), inspiratory time (Ti), peak inspiratory pressure (PIP), and peak inspiratory flow (Fpki) displayed on the ventilator control panel; tidal volume (VT), calculated from the displayed minute volume, and identical parameters measured by the pulmonary mechanics system at each body weight, were compared using a two factor analysis of variance. Significant differences (P< 0.05) were found between mean displayed and measured values for RR, PIP, and Fpki.     

Respiratory mechanics in Standardbred horses with sub-clinical inflammatory airway disease and poor athletic performance

The aim of this study was to investigate and quantify respiratory mechanical dysfunctions in Standardbred horses with both poor performance and bronchoalveolar lavage fluid cytology characteristic of inflammatory airway disease (IAD). A control group of healthy Standardbred horses was compared. Respiratory mechanics and breathing pattern were examined at rest and during hyperventilation induced using a rebreathing method. At rest, respiratory mechanics and breathing pattern were superimposable in both groups. In IAD horses, rebreathing increased ventilation, with larger tidal volumes and lower respiratory frequencies. During hyperventilation, IAD animals showed frequency-dependent dynamic lung compliance, and had greater viscous lung resistance and rate of dynamic work of breathing. As IAD alters pulmonary mechanics, the ventilatory load increases and horses requiring significantly higher energy for breathing may suffer restrictions in their athletic performance. This rebreathing method permits early evaluation of respiratory mechanical dysfunction in poorly performing horses with sub-clinical IAD.     

Influence of breathing pattern and lung inflation on impulse oscillometry measurements in horses

The objective of this paper was to determine if changes in ventilation patterns could influence the outcome of respiratory function measurements performed with our impulse oscillometry system (IOS) in horses. In a first study, IOS tests were performed in vitro on six isolated equine lungs. Lung inflation levels were controlled by modifying depressurisation inside an artificial thorax and different ventilation patterns were imposed. In a second in vivo study, transient variations in breathing pattern were evaluated both with the IOS and a current reference technique (CRT) in five healthy mature horses after an intravenous (i.v.) injection of lobeline hydrochloride. In both studies, respiratory rate (RR, range: 7-42 breaths/min.) and tidal volume (V(T), range: 0.4-25 L) had minor or no influence on IOS parameters. The influence of lung inflation, most marked for resistance at 5 Hz (R(5 Hz)), was limited for the considered physiological range. In vivo, statistical models indicated that maximal changes in pleural pressure (Max Delta Ppl) and peak flows were the main determinants of the variability of the resistance (R(rs)) and the reactance (X(rs)) of the respiratory system. The fourfold increase in baseline Max Delta Ppl and peak flows obtained during hyperpnoea caused a significant increase in R(rs) at 5 and 10 Hz and a decrease in X(rs) at all frequencies. We conclude that IOS parameters are not influenced by tachypnoea, but will reflect alterations in respiratory mechanics caused by hyperpnoeic breathing.     

Efficacy of sustained release needle-less ceftiofur sodium implants in treating calves with bovine respiratory disease

Three experiments were conducted to determine preliminary efficacy of sustained release needle-less implants in effecting cure in calves with bovine respiratory disease. One hundred and twenty beef calves with a rectal temperature > or = 40 degrees C and shallow or labored respiration and coughing were used in these experiments. Four groups (1-ceftiofur sodium injections [days 1, 2, and 3], 2-ceftiofur sodium needle-less implants [days 1, 2, and 3], 3-ceftiofur sodium needle-less implants [days 1 and 3], and 4-ceftiofur sodium needle-less implants [day 1] were included. All treatments contained 250 mg of ceftiofur sodium and were administered intramuscularly in the neck after diagnosis of bovine respiratory disease. Experiment 1 included 20 calves (group 1-10 calves and group 3-10 calves; 213 to 255 kg) and calves were monitored for clinical efficacy. Experiment 2 included five calves per group (all four groups; 164 to 192 kg) and calves were bled frequently after treatment for desfuroylceftiofur (the primary ceftiofur metabolite) concentrations. Experiment 3 included 20 calves per group (all four groups; 160 to 205 kg) and calves were monitored for clinical efficacy. Blood desfuroylceftiofur concentrations remained above the minimum inhibitory concentration for Pasteurella haemolytica, Pasteurella multocida, and Haemophilus somnus for 24 hours after injection and 72 hours after implantation (P < 0.05). Mortalities and the number of calves with a positive response and relapse response were similar (P < 0.25) among the four groups. In summary, the administration of one-250 mg ceftiofur sodium needle-less sustained release implant was as efficacious in treating bovine respiratory disease as three daily 250 mg injections of ceftiofur sodium.     

Plethysmographic comparison of breathing pattern in heaves (recurrent airway obstruction) versus experimental bronchoconstriction or hyperpnea in horses

BACKGROUND: Horses with recurrent airway obstruction (heaves) are described as exhibiting "increased abdominal effort," but it is unknown whether this translates to an effective contribution to ventilation. HYPOTHESIS: We hypothesized that heaves is characterized by asynchrony between rib cage and abdominal motions, and that the abdominal component is the major contributor to ventilation. ANIMALS: The rib cage versus abdominal motion in naturally occurring heaves (n = 15) was compared to controls at rest (n = 7) and during hyperpnea because of lobeline treatment, and the effects of histamine-induced bronchoconstriction in controls (n = 10). METHODS: Flow patterns, phase angle (theta) between the rib and abdominal compartments, abdominal (Vabd) contribution to tidal volume (VT), and lung mechanics were measured. RESULTS: Findings unique to the heaves group included the loss of biphasic expiratory flow, severely increased theta with the abdomen consistently lagging behind the rib cage, and a reduced contribution of the abdomen to ventilation. A subgroup of heaves (n = 5) with abdominal paradox showed a significant (P < .05) reduction in tidal volume, and increased respiratory rate. Bronchodilation reduced theta in heaves (P = .06), but theta remained significantly higher after bronchodilation than found in controls. CONCLUSIONS AND CLINICAL IMPORTANCE: We conclude that breathing pattern in horses with heaves is characterized by severe rib cage/abdominal asynchrony, with the rib cage motion in synchrony with flow, therefore dominating ventilation. In a subset of heaves, the abdominal compartment (diaphragm, abdominal muscles) was completely out of synchrony with flow ("abdominal paradox") despite the clinical appearance of "increased abdominal effort."     

Experimental reproduction of respiratory tract disease with bovine respiratory syncytial virus

An experiment was conducted to reproduce respiratory tract disease with bovine respiratory syncytial virus (BRSV) in one-month-old, colostrum-fed calves. The hypothesized role of viral hypersensitivity and persistent infection in the pathogenesis of BRSV pneumonia was also investigated. For BRSV inoculation a field isolate of BRSV, at the fifth passage level in cell culture, was administered by a combined respiratory tract route (intranasal and intratracheal) for four consecutive days. Four groups of calves were utilized as follows: Group I, 6 calves sham inoculated with uninfected tissue culture fluid and necropsied 21 days after the last inoculation; Group II, 6 calves inoculated with BRSV and necropsied at the time of maximal clinical response (4-6 days after the last inoculation); Group III, 6 calves inoculated with BRSV and necropsied at 21 days after the last inoculation; Group IV, 6 calves inoculated with BRSV, rechallenged with BRSV 10 days after initial exposure, and necropsied at 21 days after the initial inoculation. Clinical response was evaluated by daily monitoring of body temperature, heart rate, respiratory rate, arterial blood gas tensions, hematocrit, total protein, white blood cell count, and fibrinogen. Calves were necropsied and pulmonary surface lesions were quantitated by computer digitization. Viral pneumonia was reporduced in each principal group. Lesions were most extensive in Group II. Disease was not apparent in Group I (controls). Significant differences (p less than 0.05) in body temperature, heart rate, respiratory rate, arterial oxygen tension, and pneumonic surface area were demonstrated between control and infected calves. Results indicate that severe disease and lesions can be induced by BRSV in one-month-old calves that were colostrum-fed and seropositive to BRSV. BRSV rechallenge had minimal effect on disease progression. Based on clinical and pathological response, results did not support viral hypersensitivity or persistent infection as pathogenetic mechanisms of BRSV pneumonia.     

Pulmonary function in dogs after intercostal thoracotomy: comparison of morphine, oxymorphone, and selective intercostal nerve block

A thoracotomy was performed at the left 5th intercostal space in 24 dogs. Dogs were assigned to 4 groups of 6 dogs each. Postoperative analgesia was administered as follows: group 1--control, no analgesia; group II--morphine (0.5 mg/kg of body weight); group III--oxymorphone (0.1 mg/kg); group IV--selective intercostal nerve block with bupivacaine HC1. Respiratory rate, minute volume (VE), and arterial blood gases were measured during the recovery period. Ventilation-perfusion mismatch was estimated by calculation of the alveolar-arterial oxygen tension difference. Arterial carbon dioxide tension (Paco2) in the control and selective intercostal nerve block groups remained within the normal range and did not differ significantly (P less than 0.05) between groups. During the first 60 to 90 minutes after surgery, Paco2 tension was increased significantly (P less than 0.05) in the groups given morphine and oxymorphone. Hypoventilation in the groups given narcotics resulted from significant reductions (P less than 0.05) in the respiratory rate and VE and produced significant (P less than 0.05) respiratory acidosis and hypoxemia. Three dogs in the groups given narcotics had a panting response that resulted in increased respiratory rates and VE. This response did not improve alveolar ventilation in these dogs, which was evidenced by increased Paco2 values. Hypoventilation, respiratory acidosis, and hypoxemia in the groups given narcotics improved significantly with time, presumably because of drug clearance. Values for alveolar-arterial oxygen tension difference indicated moderate ventilation-perfusion mismatch secondary to anesthesia in all groups; however, significant differences (P less than 0.05) between the groups were not observed.     

Effect of supplemental chromium on antibody responses of newly arrived feeder calves to vaccines and ovalbumin.

Two trials were conducted to investigate the effects of supplemental chromium (Cr) from organic sources (Cr chelate and high Cr yeast) on antibody responses of newly arrived feeder calves following vaccination with infectious bovine rhinotracheitis (IBR), para-influenza-3 (PI3), bovine respiratory syncytial virus (BRSV), bovine viral diarrhea (BVD) and Pasteurella haemolytica and ovalbumin (OVA). Using cross bred steer calves purchased at sales in Ontario, vaccines and OVA were given on d 0 and 21 after arrival in the feedlot. Immune responses of calves were measured as serum specific antibody titres against all antigens on d 0 and 28 or d 35. The anti-OVA antibody responses (trial 2) were further investigated by measuring antibody concentrations of calves weekly until d 55 after arrival in the feedlot. Supplemental Cr (0.14 ppm) from an amino acid-chelated source had no effect on antibody responses to IBR, P13 and BRSV, but enhanced (P < 0.05) antibody titres of calves in response to the BVD vaccine on d 28 or d 35. Supplemental Cr from Cr yeast had no effect on antibody titres of calves to any vaccines. Chromium from both sources (trial 1 and 2) had no effect on antibody responses of calves following vaccination with P. haemolytica. However, supplemental Cr (0.75 ppm) from Cr yeast enhanced (P < 0.05) serum antibody responses of calves to OVA during the primary response (d 14) and secondary response (d 35) following immunization. These data confirmed our previous finding that supplemental Cr can enhance humoral immune response of market-transit stressed calves, but its enhancement on vaccine efficacy was antigen-dependent and variable.     

Field trials on a live bovine respiratory syncytial virus vaccine in calves.

Field trials were carried out in calves using a live bovine respiratory syncytial (BRS) virus vaccine prepared from the attenuated BRS virus, strain rs-52. Two hundred seventy-five and 353 calves were vaccinated intranasally and intramuscularly, respectively. No undesirable postvaccinal reactions were observed in the vaccinated calves. Of the serum neutralizing (SN) antibody negative calves 89.7% (26/29) and 92.8% (90/97) developed SN antibody 1 month after intranasal and intramuscular vaccination, respectively. Most of the calves having SN antibody titers of 1:1 or 1:2 at the time of vaccination showed a significant increase in SN antibody titer. About 70% and 90% of the calves vaccinated intranasally and intramuscularly, respectively, maintained SN antibody for 6 months after vaccination. In a field trial, a natural BRS virus infection occurred about 5 months after the start of the trial. Ten of the 16 unvaccinated control calves showed respiratory symptoms due to BRS virus infection. On the contrary, all of the 68 vaccinated calves exhibited no symptoms at all, indicating efficacy of the vaccine.     

Protection against respiratory disease in calves induced by vaccines containing respiratory syncytial virus, parainfluenza type 3 virus, Mycoplasma bovis and M dispar

A field trial to assess the ability of two vaccines to protect calves against respiratory disease was carried out on a large beef rearing unit in southern England over the two winters of 1983 to 1984 and 1984 to 1985. A quadrivalent vaccine containing the killed antigens of respiratory syncytial virus, parainfluenza virus type 3, Mycoplasma bovis and M dispar or a vaccine containing only the respiratory syncytial virus component were inoculated into 246 and 245 calves, respectively; 245 calves remained as unvaccinated controls. The calves were reared in seven batches and outbreaks of disease occurred in five; significant protection was achieved in the four batches in which disease was associated with respiratory syncytial virus and M bovis infection, together or independently. The death rate from pneumonia was 9 per cent in the control group, 2 per cent in the calves inoculated with the quadrivalent vaccine (P less than 0.001), a protection rate of 77 per cent, and 3 per cent in the calves inoculated with the respiratory syncytial virus vaccine (P less than 0.01), a protection rate of 68 per cent. The proportion of calves receiving treatment for respiratory disease was 38 per cent in the control group, 25 per cent in the calves inoculated with the quadrivalent vaccine (P less than 0.001) and 27 per cent in the calves inoculated with the respiratory syncytial virus vaccine (P less than 0.01). The results show that protection against respiratory disease can be achieved by parenteral vaccination of calves with the appropriate inactivated microorganisms.     

Flunixin meglumine in calves with natural bovine respiratory syncytial virus infection

Twenty-three calves (three to eight months of age) with serological evidence of bovine respiratory syncytial virus infection were used in this study. The calves originated from four herds with respiratory tract disease. In a double blind trial the calves were injected intravenously with either flunixin meglumine (2 mg/kg body weight) or with a placebo. The effect on the course of disease was measured using the PO2 in capillary blood samples from the ears of the calves and by the effect on body temperature and respiratory rate. Mean body temperature fell significantly in the flunixin meglumine treated group. Statistically significant differences were not found between the treated and control group during the seven-day examination period.     

Effect of high arterial carbon dioxide tension on efficiency of immunoglobulin G absorption in calves.

OBJECTIVES: To determine whether high PaCO2 reduced apparent efficiency of IgG absorption (AEA) in calves and whether assisted ventilation of calves with high PaCO2 increased AEA. ANIMALS: 48 Holstein calves. PROCEDURES: Arterial and venous blood samples were collected 1, 13, and 25 hours after birth; an additional venous sample was collected at 37 hours after birth. Arterial samples were analyzed for PaCO2, PaO2, pH, and bicarbonate and base excess concentrations; venous samples were analyzed for plasma IgG concentrations. On the basis of 1-hour PaCO2, calves were assigned to nonrespiratory acidosis (PaCO2 < 50 mm Hg; n = 19) or respiratory acidosis (PaCO2 > or = 50 mm Hg; 29) groups. Calves in the respiratory acidosis group were assigned randomly to receive no further treatment (n = 17) or to be given 5 minutes of assisted ventilation (12). All calves received between 1.8 and 2 L of colostrum 2, 14, 26, and 38 hours after birth. Plasma volume and AEA were determined 25 hours after birth. RESULTS: 1-hour PaCO2 had no effect on AEA or on plasma IgG concentrations determined 13, 25, or 37 hours after birth. Artificial ventilation had no effect on plasma IgG concentration or AEA. CONCLUSIONS AND CLINICAL RELEVANCE: Lack of effect of 1-hour PaCO2 on AEA and IgG concentration indicated that calves compensated for moderate acid-base imbalances associated with birth. Calves born with high PaCO2 achieved adequate plasma IgG concentrations if fed an adequate amount of high-quality colostrum early in life. The effect of artificial ventilation on PaCO2 was temporary and did not increase AEA.