Transmissibility of Mycoplasma mycoides subsp. mycoides infection from experimentally inoculated goats to other goats and calves was studied. Eight goats and six calves were housed in an 18 m2 room. Six of the goats were inoculated endobronchially with strain D44 isolated from a natural case of polyarthritis in Ontario. These six goats died within a week of Mycoplasma septicemia. The two contact goats or the six calves never showed signs of disease and M. mycoides subsp. mycoides was not recovered from these animals. The contact goats and four calves were killed 25 days after exposure. They were all seronegative, M. mycoides subsp. mycoides was not recovered at necropsy and none had pathomorphological changes attributable to this Mycoplasma. The two remaining calves were inoculated endobronchially with 10(9) CFU of strain D44 and observed for 20 days. They never showed signs of disease and did not have significant lesions at necropsy. Both developed a significant serological response to M. mycoides subsp. mycoides, although this organism was not recovered during the experimental period or at necropsy. This study did not provide evidence for transmission of M. mycoides subsp. mycoides from endobronchially inoculated goats to contact goats or calves and endobronchially inoculated calves did not develop pneumonia. This would suggest that the infection of the goat population in Canada with this pathogen would not be a significant threat to the cattle population.
Intravenous injection of Mycoplasma bovis produced in calves arthritis with synovial infiltration of lymphocytes, macrophages and neutrophils. Necrosis was observed focally around blood vessels. Joint spaces contained fibrinopurulent exudate. Parenterally vaccinated calves had a markedly reduced frequency of arthritic joints. Immunoglobulin classes and specific antibody in joint fluids were quantitatively less than in sera but significantly greater in arthritic than in normal joints. The possible mechanisms of induction of joint fluid antibody are discussed.
Epidemiological data, clinical findings, laboratory data, medical imaging, and outcomes were reviewed in 29 dairy calves with otitis media/interna. Age at admission ranged from 1 to 24 wk. The majority of calves were referred during winter. Clinical signs included drooping ear, ptosis, head tilt, abnormal nystagmus, strabismus, dysphagia, regurgitation, stiff neck, opisthotonos, facial hyperesthesia, and purulent aural discharge. Intranasal endoscopic examination of 5 animals revealed nasopharyngeal collapse in 4. Cerebrospinal fluid (CSF) was abnormal in all of 7 cases. Mycoplasma bovis was cultured from all but 1 case with external ear or tympanic bullae samples (n = 12), and Mycoplasma arginini was cultured from the remaining ear sample. Radiographs of the tympanic bullae were performed in 24 calves, tomodensitometry (CT) in 3 calves and ultrasound in 4 calves. According to medical imaging techniques or necropsy, 69% of the cases were classified as chronic. Mean duration of treatment was 23.3 d. The rate of clinical recovery was 75%.
Electron microscopy has been used to show that Mycoplasma dispar produces an external capsulelike material in vivo that has an affinity for both ruthenium red and polycationic ferritin. This extracellular material is lost upon passage in culture medium but can be regained with a single passage on bovine lung fibroblast (BLF) cells. To confirm that the extracellular material associated with cell-grown mycoplasmas was the same as that observed in infected calves, rabbit antibodies were produced to purified capsulelike material isolated by protease digestion of cell-grown organisms. These antibodies bound to capsulelike material on the surface of M. dispar cells colonizing the bronchial epithelium of infected calves and to capsulelike material from cell-grown mycoplasmas. Calves infected with M. dispar produced antibodies in lung secretions that were capable of binding to the purified capsulelike material. The Fab fragments of rabbit antibodies to in vitro-produced capsulelike material could block this binding, indicating that the capsulelike material was similar in both in vivo-grown and cell-grown organisms. The carbohydrate nature of the capsular material suggested by the ruthenium red and polycationic staining characteristics was confirmed by its binding to Ricinus communis agglutinin, a galactose-specific lectin. These studies confirm that capsule material produced during infections with M. dispar share antigenic determinants with the material produced under in vitro conditions and that association with mammalian cells induces production of this material.
A mycoplasma has been recovered from the eyes of calves in two naturally-occurring outbreaks of infectious bovine keratoconjunctivitis; also from a third group of calves accidentally exposed to an animal which had ocular exudates from one of the outbreaks instilled into its eyes.
The severity of the ocular lesions in infectious bovine keratoconjunctivis outbreaks may be related to a mixed infection with the mycoplasma and Moraxella bovis.
Preliminary typing studies indicate the mycoplasma is not serologically related to any known bovine mycoplasma.
This report describes the incidence of Mycoplasma dispar, ureaplasma and conventional (large colony) mycoplasma isolated from the pneumonic lungs of groups of young calves and the identification to species level of mycoplasmas in mixed populations with the aid of the indirect fluorescent antibody test. Pneumonic lung tissue yielded one or more mycoplasma species from 88% of the 153 calves cultured. The mycoplasmas identified and percent of the calves with lungs positive for each species were: M. dispar (56%), ureaplasma (44%), Mycoplasma bovis (37%), Mycoplasma arginini (33%) and Mycoplasma bovirhinis (23%). Conventional mycoplasmas isolated from two calves (1%) could not be identified using the antisera available.
The effect of ambient temperature and humidity on the structure of respiratory epithelium of calves was studied. Four calves of each of three experiments were acclimatized to a nonoperational environmental chamber for six days and then exposed to constant extremes of temperatures and relative humidity of one of 30 degrees C --35%, or 27 degrees C--92%, or 5 degrees C--92% respectively in this chamber for eight days each. Five calves (3 and 2) were similarly acclimatized then exposed to 1 degrees C--40%. Nasal swabs were taken from all animals at regular intervals. Swabs of three animals yielded Mycoplasma spp. and one swab yielded the virus of infectious bovine rhinotracheitis. Detailed histological studies of respiratory epithelium of nose, trachea, major bronchus and terminal bronchioli were conducted at four sites. Goblet cells were least in calves held in hot and dry air; calves held in dry air had the least polymorphonuclear cells and the greatest prevalence of hypochromatic cell layers and vacuolation of epithelial cells. Differences between experiments were evident most for sites of trachea and major bronchus.
Seven experiments with four calves each were conducted in which the calves spent at least four days of adaptation in an environmental chamber and then were subjected to climatic stress in the form of a number of constant ambient temperature and humidity combinations. On the second day of climatic stress the calves were individually exposed to measured numbers of infectious units of bovine herpesvirus 1 (BHV1, virus of infectious bovine rhinotrachetis) in aerosol. The calves were killed seven or eight days later. Mycoplasma were found in some nasal swabs and in one lung. Certain bacteria but no Pasteurella were often isolated from the lungs. Bovine herpesvirus 1 was isolated from chamber air and from most postinoculation nasal swabs, tracheas and lungs. The number of macro- and microscopic lesions did not appear to be influenced by the climatic conditions of the experiments. The histopathological changes in epithelium at all levels of the respiratory tract were described in detail.
Mycoplasma agalactiae subsp. bovis strain Iowa 1136 was isolated from synovial fluids of a clinical case of arthritis in cattle on pasture in Iowa. When given to calves and cows by intra-articular or intravenous injection, it caused severe and persistent joint infections with fever, lameness, and swelling of the affected joints, plus synovitis, tendonitis, and fibrinous-purulent synovial fluids of high protein content. Intramammary administration of the organism caused severe mastitis. Calves nursing the cows developed severe mycoplasmal arthritis.
One or both eyes of 20 calves were inoculated one or more time with variou(s combinations of microorganism (live oor killed Moraxella bovis, infectious bovine rhinotracheitis virus, bovine adenovirus, bovine parainfluenza-3 virus and Mycoplasma bovoculi) by conjunctival instillation or direct inoculation of the conjunctivea or cornea. The eyes of all the calves received natural or artificial ultraviolet irradiation. Neither the adenovirus nor parainfluenza-3 virus became established in the eye or produced keratoconjunctivitis. Both M. bovis and infectious bovine rhinotracheitis virus became established in the bovine eye and produced disease. Subconjunctival or intracorneal inoculation of M. bovis caused a severe disease, simulating natural infectious bovine keratoconjunctivitis. Only the intracorneal inoculation of mycoplasma produced severe keratoconjunctivits. Eyes that on initial exposure to M. bovis became severly inflamed were more resistant to a second or third exposure to M. bovis, presumably by enhanced local defence mechanisms.
Mycoplasma alkalescens is an arginine-metabolizing mycoplasma, which has been found in association with mastitis and arthritis in cattle. Routine bacteriological examination of 17 bronchoalveolar lavage samples from calves with pneumonia in a single herd in Denmark, identified M. alkalescens in eight samples. The organism was found as a sole bacterilogical findings in five of the samples as well as in combination with Mannheimia haemolytica, Haemophilus somni and Salmonella Dublin. This is the first report of isolation of M. alkalescens in Denmark.
Infection by Mycoplasma bovis (M. bovis) can induce diseases, such as pneumonia and otitis media in young calves and mastitis and arthritis in older animals. Here, we report the finished and annotated genome sequence of M. bovis strain Hubei-1, a strain isolated in 2008 that caused calf pneumonia on a Chinese farm. The genome of M. bovis strain Hubei-1 contains a single circular chromosome of 953,114 bp with a 29.37% GC content. We identified 803 open reading frames (ORFs) that occupy 89.5% of the genome. While 34 ORFs were Hubei-1 specific, 662 ORFs had orthologs in the M. bovis type strain PG45 genome. Genome analysis validated lateral gene transfer between M. bovis and the Mycoplasma mycoides subspecies mycoides, while phylogenetic analysis found that the closest M. bovis neighbor is Mycoplasma agalactiae. Glycerol may be the main carbon and energy source of M. bovis, and most of the biosynthesis pathways were incomplete. We report that 47 lipoproteins, 12 extracellular proteins and 18 transmembrane proteins are phase-variable and may help M. bovis escape the immune response. Besides lipoproteins and phase-variable proteins, genomic analysis found two possible pathogenicity islands, which consist of four genes and 11 genes each, and several other virulence factors including hemolysin, lipoate protein ligase, dihydrolipoamide dehydrogenase, extracellular cysteine protease and 5′-nucleotidase.
The purpose of this study was to determine the presence of Hemophilus somnus, Mycoplasma bovis, Mannheimia hemolytica, and bovine viral diarrhea virus (BVDV) in lesional tissues of feeder calves dying with myocarditis. Tissues from the heart and lungs of 92 calves dying with myocarditis in Alberta feedlots were immunohistochemically stained for the antigens of these agents. Tissues from 44 calves dying from noninfectious causes and 35 calves dying with pneumonia were tested as controls. Hemophilus somnus was found in cardiac lesions in the majority of myocarditis cases (70/92). Mycoplasma bovis was concurrently demonstrated in the hearts of 4/92 affected calves. No bacterial pathogens were found in heart tissues from the control groups of calves. Bovine viral diarrhea virus was demonstrated in the tissues of 4/92 myocarditis cases compared with those of 13/35 calves dying from pneumonia and 0/44 calves dying from noninfectious causes. The results demonstrate that H. somnus is the principle pathogen associated with myocarditis in feedlot calves and that the presence of BVDV is more common in these calves compared with calves dying of noninfectious causes. The findings also suggest that BVDV is an important pathogen in calves dying with gross postmortem lesions of pneumonia.
Acrylamide gel electrophoresis was used to show the similarities and differences in the membrane proteins of two vaccine and two virulent strains of Mycoplasma mycoides var. mycoides. Immunoelectrophoretic (IEP) analysis was also used to partially characterize the associated antigens. Antibody spectra to the antigens of M. mycoides differ in rabbit, pig, and cattle sera. Rabbits produce better precipitating antibody against the anodic migrating protein mycoplasma antigens than cattle and pigs as seen in IEP. However, rabbit anti-M. mycoides serum did not show precipitating antibody against the heat-stable carbohydrate antigen. As judged by IEP, the major carbohydrate antigen extracted from the media, or boiled whole organism, is similar to that present in the sera-infected cattle and knee joints of calves. This carbohydrate antigen has a cathodic migration in IEP at pH 8.6. Periodate oxidation, classically used to destroy carbohydrate, also destroys most of the protein antigens. Heating the antigens to 56 C for 10 min destroys many of the noncarbohydrate antigens and 100 C eliminates all but the carbohydrate antigen. Extraction of M. mycoides with chloroform-methanol, phenol, ethanol, or ethanol-acetone reduced or eliminated most of the protein antigens. Some of the isolated antigenic fractions of M. mycoides were tested to determine their activity in the diagnostic complement fixation test for contagious bovine pleuropneumonia and their inhibitory effect in this test by using bovine anti-M. mycoides antisera having precipitating antibody and circulating antigen. The complement fixation antigen is not the galactan, cannot be extracted by chloroform-methanol, but is stable to boiling at 100 C and may be extracted by phenol and partially precipitated by ethanol-acetone.
The mycoplasmas (formerly called pleuropneumonia-like organisms, or pplo) are a group of pleomorphic micro-organisms characterized by lack of cell wall and ability to form colonies on agar resembling tiny fried eggs. They have been recognized as pathogens of lower mammals since 1898. Of the more than 40 known veterinary species, many are pathogens, commonly causing pneumonia, arthritis or arteritis. Of the mycoplasmas found in man, Mycoplasma pneumoniae is the only well established human pathogen. It is responsible for a variety of respiratory syndromes, of which the most frequently recognized is cold agglutinin-positive atypical pneumonia. Hematologic, neurologic and dermatologic complications of this infection have been noted. M. hominis has been implicated as a causative factor in various febrile complications of pregnancy, such as septic abortion and amnionitis. T-strain mycoplasmas are ubiquitous in the human genitourinary tract, but attempts to link their presence to disease have thus far been unsuccessful. Mycoplasmas also have been associated with neoplastic disease and with rheumatoid arthritis. The validity of these latter findings is unclear, and additional study is needed.
Proteins translocated across the single plasma membrane of mycoplasmas (class Mollicutes) represent important components likely to affect several interactions of these wall-less microbes with their respective hosts. However, identification and functional analysis of such proteins is hampered by the lack of mutational systems in mycoplasmas and by a perceived limitation in translating recombinant mycoplasma genes containing UGA (Trp) codons in other eubacteria. Here we directly analyze a gene encoding a Mycoplasma hyorhinis protein capable of promoting its membrane translocation. It was initially detected by screening a recombinant phage genomic library with antibody from a host with M. hyorhinis-induced arthritis and was localized by Tn5 and deletion mutations affecting expression of antigenic translational products. Sequence analysis of the isolated gene predicted a hydrophilic protein, P101, containing three UGA codons and a putative signal peptide with an uncharacteristic cluster of positively charged amino acids near its C terminus. Nevertheless, lambda::TnphoA transposon mutagenesis of an Escherichia coli plasmid bearing the p101 gene resulted in p101::TnphoA fusions expressing products that could translocate as much as 48 kDa of the P101 sequence (up to the first UGA codon) across the E. coli plasma membrane. Fusion proteins containing mature P101 sequences expressed mycoplasma epitopes and were found by cell fractionation and detergent phase partitioning to be integral membrane proteins in E. coli, suggesting a lack of signal peptide cleavage in this system. Importantly, identification of P101 by direct analysis of its export function relied neither on prior identification of the mycoplasmal product nor on complete expression of the product from the cloned mycoplasma gene.
Calves from five Ontario feedlots were bled on arrival and approximately 28 days later. Calves treated during this interval for undifferentiated respiratory disease were classified as cases and untreated calves were classified as controls. Serum was titrated blindly for antibodies to Mycoplasma bovis and Mycoplasma dispar. Indirect hemagglutination titers of 1:20 or more were assumed to reflect recent or current exposure, whereas 1:10 or less were not. The titers to M. bovis increased in all feedlots indicating active infection. The initial titers to M. dispar were higher than the titers against M. bovis, yet they increased in all feedlots except one, suggesting widespread infection with this organism. There was an increased risk (although not statistically significant) of being treated if the titer against M. bovis rose during the period. Calves with low M. dispar titers on arrival were at increased risk of being treated and titer increases were strongly associated with treatment (statistically significant). Thus, the serological results indicate high prevalence of M. bovis and M. dispar in the feedlot calves and that calves with increasing titers in particular to M. dispar are at increased risk of being treated for respiratory disease.
Three species of mycoplasma have been established as being of importance as causes of pneumonia in housed calves, based on pathogenicity studies and frequency of association with the disease. These three species are Mycoplasma bovis, M. dispar, and Ureaplasma diversum. M. bovis is the most pathogenic of these species but the disease outbreaks with which it is associated are sporadic. M. dispar is regularly isolated from pneumonic calves but is also found causing mild superficial and asymptomatic infections of the respiratory mucosa. The bovine ureaplasmas are serologically complex. They are distinct from ureaplasmas isolated from other non-ruminants by PAGE analysis, G + C content of DNA, and serology. A second species within the genus ureaplasma has been proposed to accommodate the bovine ureaplasmas, U. diversum. Control of mycoplasma respiratory infections of cattle based on immunization might be possible. Calves have been immunized against M. bovis and immunity has been related to antibody in the lung. M. dispar appears less immunogenic in calves than M. bovis and this may contribute to its pathogenicity.
Ocular deposits of immune complexes are believed to contribute to the anterior segment inflammations observed in association with the human arthritides. Arthritis-related ocular inflammations may be reproduced in animals by infection with certain species of mycoplasma. To evaluate the role of immune complexes in the production of ocular lesions, we studied their involvement in the rodent model of experimental arthritis-associated ocular inflammation induced by Mycoplasma arthritidis. Sprague-Dawley rats were infected with viable concentrates of M. arthritidis and monitored for the production of related circulating and intraocular immune complexes. Circulating immune complexes were monitored by antigen capture systems, and localized intraocular complexes were identified by indirect immunohistochemistry. Polyacrylamide gel immunoblot analysis of captured complexes confirmed the antigen(s) involved as proteins derived from M. arthritidis. Indirect immunofluorescence revealed localized complexes containing mycoplasma antigens within the ciliary-iris vasculature. Concentrations of the generated complexes diminished rapidly over a 30-day period. While complex deposits within ocular tissues could represent a contributing cause to the localized anterior segment inflammation reported in this rodent model, secondary challenge with viable M. arthritidis, which reproduced high concentrations of intraocular and circulating immune complexes, failed to elicit any ocular response.
When injected into mice, Mycoplasma arthritidis causes a chronic arthritis that resembles rheumatoid arthritis, histologically. The organism produces a superantigen termed Mycoplasma arthritidis mitogen or MAM, that in humans preferentially expands T cells whose antigen receptors express V beta 17. T cells with this phenotype appear to be increased in rheumatoid synovial effusions. We describe a novel approach to isolating and characterizing human MAM-reactive T-cell lines and determining their T-cell receptor (TCR) V beta usage. Lines were prepared from T cells that clustered with dendritic cells during a 2-day exposure to MAM. Cluster and noncluster fractions of T cells were then expanded by using feeder cells and a polyclonal mitogen. Most of the MAM reactivity was found in dendritic T-cell clusters, as were most of the T cells expressing TCR V beta 17. After expansion, 76% of the cluster-derived T-cell lines were MAM reactive, while no reactivity was seen in cell lines derived from the noncluster fraction. Of the MAM-reactive lines, 49% expressed V beta 17 on some or all of the cells. Cell lines from both cluster and noncluster fractions were analyzed for TCR V beta mRNA expression by PCR amplification. Other V beta genes (5.1, 7, 8, 12, and 20) were found to be expressed by lines that were MAM reactive, although these were not a major component of the cluster-derived T cells. Some non-cluster-derived lines expressed V beta s 17, 12, and 7, but these proved to be nonreactive to MAM. Therefore, dendritic cells can be used to immunoselect and characterize T cells that express superantigen-reactive TCRs.
Mycoplasmas may be associated with rheumatoid arthritis in various animal hosts. In humans, mycoplasma arthritis has been recorded in association with hypogammaglobulinemia. Mycoplasma fermentans is one mycoplasma species considered to be involved in causing arthritis. To clarify which mycoplasmal compounds contribute to the inflammatory, bone-destructive processes in arthritis, we used a well-defined lipopeptide, 2-kDa macrophage-activating lipopeptide (MALP-2) from M. fermentans, as an example of a class of macrophage-activating compounds ubiquitous in mycoplasmas, to study its effects on bone resorption. MALP-2 stimulated osteoclast-mediated bone resorption in murine calvaria cultures, with a maximal effect at around 2 nM. Anti-inflammatory drugs inhibited MALP-2-mediated bone resorption by about 30%. This finding suggests that MALP-2 stimulates bone resorption partially by stimulating the formation of prostaglandins. Since interleukin-6 (IL-6) stimulates bone resorption, we investigated IL-6 production in cultured calvaria. MALP-2 stimulated the liberation of IL-6, while no tumor necrosis factor was detectable. Additionally, MALP-2 stimulated low levels of NO in calvaria cultures, an effect which was strongly increased in the presence of gamma interferon, causing an inhibition of bone resorption. MALP-2 stimulated the bone-resorbing activity of osteoclasts isolated from long bones of newborn rats and cultured on dentine slices without affecting their number. In bone marrow cultures, MALP-2 inhibited the formation of osteoclasts. It appears that MALP-2 has two opposing effects: it increases the bone resorption in bone tissue by stimulation of mature osteoclasts but inhibits the formation of new ones.
Synovial needle biopsies, joint aspirates, and joint tissue obtained at open operation from 41 cases of rheumatoid arthritis were inoculated onto PPLO media, L-form medium, and cell cultures for the isolation of mycoplasmas, L-form bacteria, and viruses. Medium suitable for the isolation of 'T' strain mycoplasmas was not employed. No mycoplasmas, L-form bacteria, or cytopathogenic viruses were shown. Similar specimens from nine patients diagnosed as having Reiter's disease were examined in a like manner and yielded only one Mycoplasma hominis type 1 isolate from a knee joint biopsy. It is concluded that known strains of mycoplasma and bacterial L-forms do not play a direct role in early and established cases of rheumatoid arthritis. Some of the cell cultures used in this study contained mycoplasma contaminants. Bacterial contaminants were also encountered in occasional batches of L-form medium.
Serial nasopharyngeal swab and bronchoalveolar lavage cultures were used to estimate changes in the bacterial flora of the respiratory tracts of calves during the first month after arrival in the feedlot. Bronchoalveolar lavage (BAL) differential cell counts served to evaluate pulmonary inflammatory changes during this period. Two groups of calves were studied, one consisting of clinically normal controls (n = 60), the other, of cases (n = 59) which received treatment for respiratory disease (penicillin +/- trimethoprimsulfadoxine). A variety of organisms, including Pasteurella multocida, Pasteurella haemolytica, Haemophilus somnus, Mycoplasma bovis and Mycoplasma bovirhinis, were present in the upper and lower airways of both groups during the postarrival period. With the exception of M. bovis, an overall decline in the prevalence of these organisms was observed during the course of the study. In cases, there was a marked decrease in the number of Pasteurella spp. and H. somnus isolates immediately following treatment. For the Pasteurella spp., however, this effect was shortlived as they often appeared to recolonize the respiratory tract within eight days of terminating antimicrobial therapy. Treatment did not appear to affect the frequency of isolating M. bovis. Its prevalence, in both groups of calves, increased to levels approaching 100% during the course of the study. All Pasteurella spp. isolates were tested for susceptibility to several commonly used antimicrobials. Resistance was only evident among P. haemolytica isolated from cases and in every instance this was to a combination of penicillin, ampicillin and tetracycline. Significantly more isolates were resistant after treatment than before. There were BAL differential cell count abnormalities indicative of inflammation in both cases and controls.(ABSTRACT TRUNCATED AT 250 WORDS)
Samples obtained by bronchoalveolar lavage (BAL) were used to evaluate pulmonary cytology in 59 feedlot calves with clinical signs of respiratory disease (cases) and 60 clinically normal comparison calves (controls). Many calves in both case and control groups had inflammatory changes in the lower respiratory tract, as determined by changes in proportions in the BAL differential cell count. Approximately 35% of cases and 40% of controls showed a normal differential cell count. It therefore appeared that the criteria used to select cases for treatment, which were similar to those often used in the field, were poor predictors of lower respiratory tract disease. A positive association was found between an increased proportion of neutrophils in BAL fluid and isolations of Pasteurella multocida and Mycoplasma bovis from BAL fluid.
During 1983-85, 279 calves requiring treatment for bovine respiratory disease and 290 comparison (control) animals from 15 different groups of feedlot calves were bled on arrival and again at 28 days postarrival. Their sera were then analyzed for antibodies to seven putative respiratory pathogens. On arrival, the prevalences of indirect agglutination titers to Pasteurella haemolytica, P. haemolytica cytotoxin, Mycoplasma bovis and M. dispar were greater than 50%, the prevalence of titers to bovine virus diarrhea virus (BVDV) was approximately 40%, and the prevalences of titers to infectious bovine rhinotracheitis virus (IBRV), bovine respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV3) were all below 25%. Seroconversion during the first month after arrival occurred in more than half the calves to P. haemolytica cytotoxin, PIV3 and RSV. Seroconversion of agglutination titers to P. haemolytica, Mycoplasma and BVDV occurred in about 40% of calves, and seroconversion to IBRV was infrequent (less than 5%). Initial titers were negatively correlated to subsequent titer changes within organism. Initial titers, and titer changes between organisms were essentially independent. Light calves had an increased risk of being selected for treatment for respiratory disease. Seroconversion to P. haemolytica cytotoxin, RSV and BVDV were predictive of respiratory disease cases, explaining approximately 69% of all respiratory disease cases in the feedlots. It was not possible to accurately predict weight gain or relapse from the serological data.