Evaluation of respiratory disease in calves: comparison of disease response to different viruses

Comparison of physiological markers, behavior monitoring, and clinical illness scoring as indicators of an inflammatory response in beef cattle

Clinical illness (CI) scoring using visual observation is the most widely applied method of detecting respiratory disease in cattle but has limited effectiveness in practice. In contrast, body-mounted sensor technology effectively facilitates disease detection. To evaluate whether a combination of movement behavior and CI scoring is effective for disease detection, cattle were vaccinated to induce a temporary inflammatory immune response. Cattle were evaluated before and after vaccination to identify the CI variables that are most indicative of sick cattle. Respiratory rate (H2 = 43.08, P < 0.0001), nasal discharge (H2 = 8.35, P = 0.015), and ocular discharge (H2 = 16.38, P = 0.0003) increased after vaccination, and rumen fill decreased (H2 = 20.10, P < 0.0001). Locomotor activity was measured via leg-mounted sensors for the four days preceding and seven days following vaccination. A statistical model that included temperature, steps, lying time, respiratory rate, rumen fill, head position, and excess saliva was developed to distinguish between scores from before and after vaccination with a sensitivity of 0.898 and specificity of 0.915. Several clinical illness signs were difficult to measure in practice. Binoculars were required for scoring respiratory rate and eye-related metrics, and cattle had to be fitted with colored collars for individual identification. Scoring each animal took up to three minutes in a small research pen; therefore, technologies that can automate both behavior monitoring and identification of clinical illness signs are key to improving capacity for BRD detection and treatment.

Clinical Scoring Systems in the Newborn Calf: An Overview

Simple Summary

Clinical scores are gaining increasing popularity in veterinary medicine thanks to their multiple advantages, which include quickness, ease, and convenience of use. This review discusses the applications of some already-known clinical scores in newborn calf management at birth and during the first weeks of age. Clinical scores are employed to assess newborn calf viability and to diagnose and monitor neonatal calf diarrhea and respiratory diseases, helping the clinician promptly recognize calves needing medical assistance. This review discusses limitations pertaining to their use and encourages efforts towards a greater consistency in definition and validation.

Abstract

A scoring system is an instrument that enables the scorers, including farmers, technicians, and veterinarians, to adopt a systematic approach for diagnosis or monitoring, as it decreases bias and confounding and increases objectivity. Practically, it is a number assigned to a patient that correlates with a probability that a diagnosis can be confirmed or that a specific outcome will follow. This article examines the clinical scores designed or adapted to bovine medicine that aim to assess newborn calf viability and to diagnose and monitor neonatal calf diarrhea and respiratory diseases, helping the clinician promptly recognize calves needing medical assistance. Despite the large number of clinical scores described in the literature, these are still barely used in farm animal practice; possibly, the complexity of the scores and missing recommendations for intervention are reasons for their lack of popularity as well as the crosswise lack of consistency among scores designed for the same purpose. Further research is needed in this regard to increase scores validation and encourage their application in bovine calf neonatology.

Determining the predictive capability of a Clinical Assessment Scoring Chart to differentiate severity of the clinical consequences of neonatal calf diarrhea relative to gold-standard blood gas analysis

Neonatal calf diarrhea (NCD) is a major problem to calf health worldwide, in terms of both morbidity and mortality. A five-point ordinal scale clinical assessment scoring (CAS) chart was utilized to assess calves suffering from NCD-related clinical abnormalities (acidosis and dehydration) on commercial farms. The objective of this research was to determine the predictive capability of this CAS chart against gold standard blood gas parameters, designed to assist farmers in the accurate assessment of the clinical consequences of NCD. A total of 443 diarrheic and non-diarrheic calves were enrolled in the study. The CAS chart rated a calf’s health from no clinical signs to varying degrees of clinical severity on a 0 (clinically normal) to 4 (grave) scale, based on clinical indicators including calf demeanour, ear position, mobility, suckle reflex, desire-to-feed, and enophthalmos. Blood gas analysis was conducted for individual calves, consisting of pH, base excess, Na⁺, K⁺, Ca²⁺, Cl⁻, glucose, total hemoglobin, bicarbonate, anion gap, and strong ion difference. Statistical evaluation was performed by comparison of the CAS score with blood gas profiles using ordinal logistic regression and a non-parametric estimation of the Receiver Operating Characteristics (ROC). The ROC analysis indicated that the CAS chart had acceptable specificity (>95%) with low sensitivity (<60%) in differentiating clinically normal from acidotic/dehydrated cases. Assessment of individual severity classes indicated that the chart can predict and differentiate both clinically normal and advanced cases from the other severity classes (peak estimations >80%) but had reduced accuracy in differentiating mild and moderate cases (peak estimations >50%). The chart, as presented, provides a simple tool to differentiate clinically normal from calves suffering the consequences of diarrhea, but fails to accurately differentiate severity for NCD related acidosis and dehydration. Further efforts are required to enhance the sensitivity and differential diagnostic value of this type of chart.

Development of a clinical scoring system for bovine respiratory disease in weaned dairy calves

Clinical scoring systems for bovine respiratory disease (BRD) in weaned dairy calves have been developed in the past with calves experimentally infected with specific respiratory pathogens. In this prevalent case control study, a BRD clinical scoring system for weaned calves was developed using field data from 689 dairy calves housed in group pens on 5 dairies in California. Of the 689 calves in the study, 89 were selected because they appeared sick based on the display of lethargy, depression, or separation from the group, whereas the remaining 600 were randomly selected. Clinical signs were recorded for all calves, and BRD case status was determined by thoracic auscultation and ultrasound examinations, which were interpreted in parallel. Of the 689 calves, 238 were identified as BRD cases. Five survey-adjusted generalized linear mixed models with a logit link function, calf as the unit of analysis, and dairy as a random intercept were assessed using 3-fold cross-validation. The best model chosen based on performance and parsimony contained the variables cough (2 points), abnormal respiration (1 point), low body condition (5 points), sunken eyes (4 points), and a 24-h ambient temperature range >15°C (1 point) with a 2-point cutoff for a BRD suspect score. An alternative model did not contain a score for the covariate 24-h ambient temperature range and had a 1-point cutoff. The best model was tested on 174 observations not used for model training and resulted in 77.0% screening sensitivity, 100% diagnostic sensitivity, and 61.9% specificity. Adding rectal temperature ≥39.2°C (102.5°F) as a second-tier test increased specificity to 76.7% and lowered the screening sensitivity to 64.8% and diagnostic sensitivity to 76.9%. The alternative model had a screening sensitivity of 84.2%, diagnostic sensitivity of 100%, and specificity of 45.7%. Adding rectal temperature ≥39.2°C (102.5°F) as a second-tier test for score-positive animals improved specificity of the alternative model to 62.6% while lowering its screening sensitivity to 70.5% and diagnostic sensitivity to 76.9%. Use of a 2-tier California BRD postweaning scoring system may provide producers and veterinarians with a new tool to monitor BRD in group-housed dairy calves. Furthermore, the scoring system may aid in judicious medical intervention for BRD cases and reduce unnecessary treatments of animals with antimicrobials.

Acute phase proteins in naturally occurring respiratory disease of feedlot cattle

The aim of this study was to evaluate three acute phase proteins (APP) [haptoglobin (HPT), lipopolysaccharide binding protein (LBP) and transferrin (Tf)] in feedlot cattle with naturally occurring respiratory disease diagnosed by a calf health scoring chart (CHSC). Seventy-seven beef calves were observed for signs of Bovine Respiratory Disease (BRD) during the first 28 days after arrival at the feedlot. Fourteen cases and pen matched controls were selected based on the CHSC. BRD cases were defined as a score of ≥ 5, while controls were defined as a score ≤ 4. The mean CHSC score in cases was 6.9 which was significantly greater than the controls 2.8 (P < 0.01). Mean plasma LBP and HPT concentrations were significantly greater in cases than controls (P < 0.01). Our study results show that measurement of HPT and LBP could be useful in detecting respiratory disease in feedlot conditions. Transferrin concentrations between the two groups were not statistically different.

Development of a novel clinical scoring system for on-farm diagnosis of bovine respiratory disease in pre-weaned dairy calves

Several clinical scoring systems for diagnosis of bovine respiratory disease (BRD) in calves have been proposed. However, such systems were based on subjective judgment, rather than statistical methods, to weight scores. Data from a pair-matched case-control study on a California calf raising facility was used to develop three novel scoring systems to diagnose BRD in preweaned dairy calves. Disease status was assigned using both clinical signs and diagnostic test results for BRD-associated pathogens. Regression coefficients were used to weight score values. The systems presented use nasal and ocular discharge, rectal temperature, ear and head carriage, coughing, and respiratory quality as predictors. The systems developed in this research utilize fewer severity categories of clinical signs, require less calf handling, and had excellent agreement (Kappa > 0.8) when compared to an earlier scoring system. The first scoring system dichotomized all clinical predictors but required inducing a cough. The second scoring system removed induced cough as a clinical abnormality but required distinguishing between three levels of nasal discharge severity. The third system removed induced cough and forced a dichotomized variable for nasal discharge. The first system presented in this study used the following predictors and assigned values: coughing (induced or spontaneous coughing, 2 points), nasal discharge (any discharge, 3 points), ocular discharge (any discharge, 2 points), ear and head carriage (ear droop or head tilt, 5 points), fever (≥39.2°C or 102.5°F, 2 points), and respiratory quality (abnormal respiration, 2 points). Calves were categorized “BRD positive” if their total score was ≥4. This system correctly classified 95.4% cases and 88.6% controls. The second presented system categorized the predictors and assigned weights as follows: coughing (spontaneous only, 2 points), mild nasal discharge (unilateral, serous, or watery discharge, 3 points), moderate to severe nasal discharge (bilateral, cloudy, mucoid, mucopurlent, or copious discharge, 5 points), ocular discharge (any discharge, 1 point), ear and head carriage (ear droop or head tilt, 5 points), fever (≥39.2°C, 2 points), and respiratory quality (abnormal respiration, 2 points). Calves were categorized “BRD positive” if their total score was ≥4. This system correctly classified 89.3% cases and 92.8% controls. The third presented system used the following predictors and scores: coughing (spontaneous only, 2 points), nasal discharge (any, 4 points), ocular discharge (any, 2 points), ear and head carriage (ear droop or head tilt, 5 points), fever (≥39.2°C, 2 points), and respiratory quality (abnormal respiration, 2 points). Calves were categorized “BRD positive” if their total score was ≥5. This system correctly classified 89.4% cases and 90.8% controls. Each of the proposed systems offer few levels of clinical signs and data-based weights for on-farm diagnosis of BRD in dairy calves.

Bovine viral diarrhea virus with deletions in the 5'-nontranslated region: reduction of replication in calves and induction of protective immunity

Bovine viral diarrhea virus (BVDV) with deletions in the 5'-nontranslated region (5'-NTR) were tested for their suitability as live BVD vaccines. Firstly, the genetic stability of the mutants was established by culturing over 15 passages in bovine cells. Secondly, two deletion mutants and the parent strain CP7-5A were characterised with respect to in vivo replication competence, attenuation and induction of protective immunity against BVDV. Naïve calves (n = 5 per group) were inoculated with mutants d2-31 and d5-57 or CP7-5A and 5 weeks later, a challenge with the BVDV type 1 strain New York was performed. The mutants were found to be genetically and phenotypically stable. Moreover, the results indicate that the mutants were attenuated with regard to effects including pyrexia and drop in leucocyte counts. Infection with the mutants induced moderate to high titers of BVDV neutralizing antibodies and completely prevented viremia after challenge infection with a heterologous BVDV strain. Taken together, the 5'-NTR deletion mutants combine a good safety profile with good efficacy and are therefore well suited as candidate live vaccines.

An inactivated bovine virus diarrhoea virus (BVDV) type 1 vaccine affords clinical protection against BVDV type 2

This study was designed to answer to two distinct questions. Firstly, is it possible to reproduce clinical signs of acute bovine virus diarrhoea virus (BVDV) type 2 infection including signs of haemorrhagic disease under experimental conditions in cattle at 20 weeks of age? Secondly, what is the extent of the protection afforded by vaccination with an inactivated BVDV type 1 vaccine against BVDV type 2 infection? Calves were vaccinated at 12 and 16 weeks of age with a commercially available inactivated BVDV type 1 vaccine (Bovilis BVD). At 20 weeks they were challenge infected with BVDV type 2 virus together with unvaccinated control calves. The unvaccinated animals developed typical signs of respiratory disease, diarrhoea with erosions and haemorrhages along the whole length gastro-intestinal tract, and depletion of lymphocytes in lymphatic organs. These signs were either absent or markedly less severe in the vaccinated animals. The beneficial effects of vaccination were most striking in the haematological parameters thrombocytopenia and leukopenia. It can be concluded that vaccination with Bovilis BVD affords cross-protection against clinical effects of a challenge-infection with heterologous type 2 BVDV.

Seroprevalence to bovine virus diarrhoea virus and other viruses of the bovine respiratory complex in Venezuela (Apure State)

Six hundred and fifteen serum samples obtained from cows in five districts of Apure State, Venezuela, were tested by ELISA for antibodies to bovine virus diarrhoea virus (BVDV). The same samples were also ELISA-tested for antibodies to bovine herpesvirus type 1 (BHV-1) and bovine respiratory syncytial virus (BRSV). Additionally, the haemagglutination-inhibition (HI) test was used for detecting antibodies to parainfluenza virus type 3 (PIV-3). Overall, seroprevalence to BVDV was 36+/-7% (SE); seroprevalence varied by district (19-42%). BHV-1 seroprevalence was 67+/-4%; variation by district was similar to that of BVDV. However, the first 80 serum samples tested by BHV-1 ELISA all had a strong background reaction with the control antigen. Therefore, these sera were adsorbed to a homogenate of non-infected bovine kidney cell line (MDBK) and retested by ELISA. The non-specific reactivity was significantly reduced (p<0.001 by Wilcoxon's signed-rank test). Compared to the virus-neutralisation (VN) test, the adsorbed BHV-1 ELISA showed 94% agreement and gave a kappa value of 0.84, indicating that the adsorption did not interfere with test accuracy. Seroprevalence against BRSV was 85+/-3%, and showed differences across districts. Most of the cows (94+/-2%) were seropositive to PIV-3, and there were no significant differences among districts.

Bovine respiratory tract disease caused by bovine viral diarrhea virus

Although several viruses and bacteria are capable of inducing bovine respiratory tract disease, a pivotal organism in the cause of this complex disease may be bovine viral diarrhea virus (BVDV). Circumstantial evidence has long supported this hypothesis. It is frequently present in diseased respiratory tract tissues often together with other viruses or bacteria. Field observations suggest marked synergism occurs. Researchers have confirmed that, in most instances, the virus itself elicits only a mild respiratory tract disease in susceptible calves, but some strains may be much more pneumo-pathogenic than others. Experimental evidence now supports the hypothesis, that BVDV markedly enhances respiratory tract disease caused by IBRV, BRSV, or Pasteurella haemolytica; that it impairs pulmonary immunity; and that it, by itself, may produce mild respiratory tract disease.

The clinical manifestations of bovine viral diarrhea infection

BVDV infections may result in a wide range of clinical manifestations ranging from subclinical infections to a severe, highly fatal form referred to as MD. In recent years, a better understanding of pathogenesis has been achieved that has allowed for a better understanding of the different clinical forms of BVDV infection. Knowledge in this area continues to evolve. The clinical forms of BVDV infections are best understood by breaking them into categories that include infections in immunocompetent cattle, fetal infections, and infections in cattle that are immunotolerant to BVDV.

Pulmonary function changes and clinical findings associated with chronic respiratory disease in calves

Thirteen field cases of chronic respiratory disease in crossbred calves aged between 1 and 8 months were subjected to a standardized examination in which clinical criteria were scored and weighted to allow quantification. Predicted values for pulmonary function variables were generated using regression equations previously established in normal calves which related measured pulmonary function variables to thoracic perimeter. Subsequent pulmonary function testing of each calf was undertaken and values obtained compared with predicted values and correlated with clinical scores. Diagnosis was confirmed at post-mortem examination. Calves with chronic respiratory disease had significantly reduced inspiratory and expiratory times, tidal volume, dynamic compliance and PaO2, significantly increased respiratory frequency, airway resistance and PaCO2 and more negative transpulmonary pressure values when compared to predicted pulmonary function values for the same calves. PaO2 and PaCO2 were the only variables correlated with clinical scores, suggesting their value in the assessment of severe cases of calf respiratory disease.

The virulence of British isolates of bovid herpesvirus 1 in relationship to viral genotype

Six strains of bovid herpesvirus 1 isolated from British cases of infectious bovine rhinotracheitis (IBR) were inoculated intranasally into calves. The clinical, virological and serological responses were measured and comparisons made between virus strains. Calves infected with viruses of subtype 1 developed more severe clinical signs and excreted higher titres of virus than calves infected with subtype 2b strains. The findings could be related to the history of IBR in Great Britain.

Levamisole-induced attenuation of alveolar macrophage dysfunction in respiratory virus-infected calves

A luminol-amplified chemiluminescence (CL) assay was used to evaluate the effect of levamisole on the metabolic activity of pulmonary alveolar macrophages (PAM) from parainfluenza-3 (PI-3) and infectious bovine rhinotracheitis (IBR) virus-infected calves. Using selective beta-adrenergic agonists and antagonists, beta 1-adrenoceptors were shown to inhibit the PAM reactive oxygen species-dependent CL response. Beta 2 adrenoceptors were apparently not important in the regulation of CL in PAM of control calves. Infection of calves with IBR virus significantly impaired beta 1-receptor function. PI-3 virus infection, in addition to disrupting beta 1-receptors, also unmasked PAM beta 2-receptor activity. Treatment of calves with levamisole, 3 mg/kg, sub-cutaneously, partially reversed the virus-induced impairment of PAM beta 1-receptor function without influencing beta 2-receptor activity. In conclusion, beta-adrenoceptors regulate bovine PAM CL response. Pulmonary viruses impair PAM beta 1-receptor function, an action which can disrupt pulmonary homeostasis. Levamisole partially restores beta-receptor effects on PAM, and may therefore be useful in the management of virus-associated bacterial pneumonia.

Lymphocyte transformation response of calves to respiratory syncytial virus

Virus-specific cell-mediated immunity, as determined by in vitro lymphocyte transformation (LT), was demonstrated in calves following infection and vaccination with respiratory syncytial virus (RSV). After experimental infection, 4 of 6 gnotobiotic calves and 6 of 21 conventional calves developed a significant LT response to RSV. By means of a whole blood assay, the LT responses of calves were examined after vaccination with an inactivated vaccine, which consisted of glutaraldehyde-fixed bovine nasal mucosa cells persistently infected with a bovine strain of RSV (GC), a live modified bovine strain of RSV (MV), or a live temperature-sensitive mutant of a human strain of RSV (ts-l). Three weeks after vaccination, a virus-specific LT response was detected in 6 of 6 calves given the GC vaccine, 0 of 4 calves given the MV vaccine, and 2 of 4 calves given the ts-l vaccine. The magnitude of the response was greatest in those animals given the GC vaccine. There was no significant correlation between the magnitude of the LT response and levels of serum neutralising antibody. However, the LT response did correlate with serum antibody measured by the single radial haemolysis test 3 weeks after the first vaccination. LT activity to RSV was associated with T and not B lymphocytes. The development of a virus-specific LT response in calves given an inactivated RSV vaccine was not associated with an increase in respiratory disease following challenge with live virus, but rather was related to increased resistance to RSV infection.

The immune response to experimental Pasteurella haemolytica infection in calves

Four male dairy calves, ages 1-9 months, were inoculated intratracheally (IT), with log dilutions (1.5 X 10(3)-1.5 X 10(6)) of an isolate of P. haemolytica A-1. Doses of bacteria varied according to ages of the calves, older calves receiving the larger doses. All four calves became severely ill within 24 h after inoculation and antibiotic treatment was considered essential. Two months later the four calves remained healthy after IT injection of P. haemolytica, again given in log dilution (2.8 X 10(2)-2.8 X 10(5)). The control calf, given a dilution of only 28 viable P. haemolytica (plate count), developed severe respiratory infection 9 days post inoculation. Antibiotic treatment was given to this calf for 7 days, at which time recovery was evident. All five calves developed direct bacterial agglutination titers to P. haemolytica. Persistent leukocyte migration inhibition indexes of all calves were decreased by greater than or equal to 20% compared to their controls. Although the initial doses administered were low, the calves became ill. Most reports refer to massive doses necessary to produce primary disease and significant agglutination titers.

Evidence for an immunocompromising effect of bovine pestivirus on bovid herpesvirus 1 vaccination

Five calves were given live intranasal vaccine against bovid herpesvirus 1 (BHV1) two days after intranasal inoculation of bovine pestivirus (BVDV). Another 5 were vaccinated in the absence of BVDV. Control unvaccinated groups were also maintained. All calves were challenged with virulent BHV1. The unvaccinated calves developed signs of infectious bovine rhinotracheitis (IBR) and both vaccinated groups showed a similar degree of clinical protection from IBR. Those given BVDV before vaccination shed up to 140 times more BHV1 (P less than 0.01) in the nasal mucus following challenge than those which had received BHV1 vaccine alone. The epidemiological significance of this is discussed.

Correlation of a disease scoring system with arterial PO2 values in respiratory syncytial virus infection in calves

The mean arterial PO2 value measured in blood obtained by puncture of the brachial artery of 20 calves with acute clinical signs of a bovine respiratory syncytial virus (BRSV) infection was 8.4 +/- 1.9 kPa. The values differed significantly from arterial PO2 values of eleven healthy calves (mean 14.2 +/- 1.5 kPa). A disease scoring system is presented based on the type of respiration and the findings on auscultation. A high correlation (r = -0.87) was found between disease scores and arterial PO2 values. This indicates that the described disease scoring system can be a useful tool in the evaluation of the severity and course of BRSV infections in calves, and could be used for evaluating the efficacy of BRSV vaccines in the field. The course of disease was studied in 127 calves with clinical signs of serologically proven BRSV infection. Animals with mild respiratory signs during the acute phase of disease remained free of severe respiratory problems until the end of a 35-day examination period. Mean disease scores indicated that animals with severe signs in the acute phase often developed persistent respiratory problems.

A comparison of three vaccines against respiratory syncytial virus in calves

An inactivated vaccine against respiratory syncytial virus (RSV) was compared with two live vaccines. The inactivated (GC) vaccine consisted of glutaraldehyde-fixed bovine nasal mucosa cells persistently infected with RSV and emulsified with oil adjuvant. The live vaccines were a modified virus (MV) derived from a bovine strain of RSV and a temperature-sensitive mutant (ts-1) derived from a human strain. The GC vaccine was inoculated subcutaneously into 12 calves and the live vaccines intramuscularly into eight calves each. Nine unvaccinated calves acted as controls. The vaccines were administered in two doses 3 weeks apart and all calves were challenged intranasally with 2 X 10(7) p.f.u. of bovine RSV 3 weeks after the second dose. At the time of challenge calves given GC, MV and ts-1 vaccines had mean serum neutralizing antibody titres of 25, 19 and 2 respectively; mean titres of IgG1 antibody by radioimmunoassay were log10 4.5, 1.3 and 2.6 respectively and mean zone areas by single radial haemolysis (SRH) were 107, 27 and 36 mm2 respectively. Eleven of 12 calves given GC vaccine were completely protected against challenge but all control animals and those given the two live vaccines were infected. The mean peak titre of virus in nasal swabs of control calves was 3.0 log10 p.f.u./ml and the mean duration of virus shedding was 6.8 days. Both these parameters were significantly reduced in animals given MV and ts-1 vaccines: mean peak titres were 2.1 and 2.4 log10 p.f.u./ml and mean duration of shedding was 3.4 and 3.3 days respectively. Thus, protection correlated better with RSV antibody detected by radioimmunoassay and SRH than with neutralizing antibody. These results are discussed in relation to the possible mechanism by which protection was mediated.

[Oral and intramuscular ferridextran intervention in male breeding calves. 3. Nutrient and feed uptake during the stay in the weaning range]

The influence of an oral and intramuscular Fe-application on the nutrient (dry matter, energy, protein and iron) and feed intake resp. (skim milk, calf rearing feed and lucerne hay) of calves during their 56-day stay in the weaning range of a rearing farm was investigated. There were significant differences between the test animal groups with regard to nutrient intake; their levels had the following sequence: B (Fe orally) greater than C (Fe i.m.) greater than A (without Fe-supplement). In the calf rearing organised as graded production the effect of iron intervention on nutrient intake probably occurs as a consequence of the reduction of the depression of feed consumption caused by disease. By comparison with the nutrient and feed intake of weaning calves from a different rearing farm one can further conclude that this secondary effect of iron intervention does not only depend on the more or less rapid remedy of the differently marked states of iron deficiency of the calves but also on the other rearing conditions (particularly the drinking regime). It is improbable that the oral ferridextran intervention (200 mg Fe/d) carried out provokes excessive iron supply.

A search for new microorganisms in calf pneumonia by the inoculation of gnotobiotic calves

In a detailed microbiological and pathological study of eight outbreaks of calf pneumonia, which included the inoculation of respiratory material into 18 gnotobiotic calves, a total of five viruses, four species of mycoplasma and 19 species of bacteria were identified. The only microorganism not previously associated with bovine respiratory disease was a Coronavirus. The experimental disease produced in the majority of the gnotobiotic calves by the intratracheal inoculation of unpassaged respiratory material, closely resembled the natural disease. However statistical analysis of the results could not ascribe the disease seen to a single microorganism or to a particular combination of microorganisms. Assuming therefore that no microorganisms were missed in the study, it was concluded that the microbiological cause of the experimental disease lay amongst the organisms already found and that one or more of three other factors, discussed in the paper, accounted for the experimental disease produced.

Symposium: disease prevention in calves. Factors affecting susceptibility of calves to disease

Enteric and respiratory disorders are the main hazards to successful calf rearing. The many interrelated factors in the etiology of these disorders are reviewed, and an attempt has been to classify the factors into those of a microbiological, immunological, nutritional, genetic, physical, or psychological nature. No one would dispute that enteric and respiratory disorders are the two main hazards to calf health, but many would argue about the relative importance of specific pathogens and other predisposing factors in the etiology of these disorders.