Diseases and pathogens associated with mortality in Ontario beef feedlots.

This study determined the prevalence of diseases and pathogens associated with mortality or severe morbidity in 72 Ontario beef feedlots in calves that died or were euthanized within 60 days after arrival. Routine pathologic and microbiologic investigations, as well as immunohistochemical staining for detection of bovine viral diarrhea virus (BVDV) antigen, were performed on 99 calves that died or were euthanized within 60 days after arrival. Major disease conditions identified included fibrinosuppurative bronchopneumonia (49%), caseonecrotic bronchopneumonia or arthritis (or both) caused by Mycoplasma bovis (36%), viral respiratory disease (19%), BVDV-related diseases (21%), Histophilus somni myocarditis (8%), ruminal bloat (2%), and miscellaneous diseases (8%). Viral infections identified were BVDV (35%), bovine respiratory syncytial virus (9%), bovine herpesvirus-1 (6%), parainfluenza-3 virus (3%), and bovine coronavirus (2%). Bacteria isolated from the lungs included M. bovis (82%), Mycoplasma arginini (72%), Ureaplasma diversum (25%), Mannheimia haemolytica (27%), Pasteurella multocida (19%), H. somni (14%), and Arcanobacterium pyogenes (19%). Pneumonia was the most frequent cause of mortality of beef calves during the first 2 months after arrival in feedlots, representing 69% of total deaths. The prevalence of caseonecrotic bronchopneumonia caused by M. bovis was similar to that of fibrinosuppurative bronchopneumonia, and together, these diseases were the most common causes of pneumonia and death. M. bovis pneumonia and polyarthritis has emerged as an important cause of mortality in Ontario beef feedlots.     

The association of titers to bovine coronavirus with treatment for bovine respiratory disease and weight gain in feedlot calves.

The association between bovine respiratory disease (BRD) and antibody titers to bovine coronavirus (BCV) was studied in 604 calves (19 different groups in 4 different feedlots from 2 provinces). Almost all calves had antibody titers on arrival in the Alberta feedlot and 82% of the calves had an antibody titer on arrival at the Ontario feedlots; titers in calves in Alberta were almost twice as high as those in calves in Ontario. The incidence of infection, in the first mo after arrival as judged by seroconversion, ranged from 61% to 100%; titer increases were much greater in calves in Ontario feedlots. Titer variables were not significantly related to BRD, except on a within-group basis (group was a confounding variable for BCV-BRD associations). Given control of group effects, calves with an antibody titer on arrival appeared to be protected against BRD for the first 28 d in the feedlot, and the association was reasonably linear over the range of titers. Each titer unit on arrival decreased the risk of BRD by about 0.8x (odds ratio). Titer change was not strongly related to the risk of BRD and the relationship was not linear over the range of titer changes. Titer change was strongly and negatively correlated with titer on arrival, and titer change was not significantly related to BRD in the presence of arrival titers. Arrival titer retained its relationship with BRD in the presence of titer data for other putative pathogens. Each higher unit of titer to BCV on arrival increased the 28-day weight gain (controlling for group, initial weight and the occurrence of BRD) by slightly more than 1 kg. Titer change was associated with decreased weight gain, when initial titer was not in the model. The lack of a linear or multivariable association between BCV titer change and BRD, and weight gain, may indicate that BCV is not a major pathogen; or, its lack of significance may merely be due to its strong correlation with arrival titer. Given the associations found in this study, particularly the interprovincial differences in arrival titers, more and different approaches to studying the possible effects of BCV on BRD are in order.     

A field trial, of preshipment vaccination, with intranasal infectious bovine rhinotracheitis-parainfluenza-3 vaccines.

A total of 849 calves, 278 controls, 335 vaccinated intranasally with IBR-PI3/TS and 236 vaccinated intranasally with IBR-PI3/PTC were studied in a field trial of preimmunization. All calves were vaccinated in Saskatchewan at least three weeks prior to shipment to feedlots. Four hundred and twenty six calves were not sold within eight weeks of vaccination; however, seven of these died within four weeks of vaccination. Treatment rates varied from 1.0% to 5.2%. There was no significant effect of vaccination on treatment rates. Similarly, there was no significant effect of vaccination in the 74 calves sold to feedlots in Saskatchewan. Three hundred and forty nine calves were sold to feedlots in Ontario. Two of these died from fibrinous pneumonia. Treatment rates varied from 1.7% to 33.3% in different feedlots, but there was no significant effect of vaccination on treatment rates. Therefore, preimmunization is unlikely to significantly reduce the overall treatment rate in calves entering feedlots.     

A comparison of florfenicol and tilmicosin for the treatment of undifferentiated fever in feedlot calves in western Canada

A field trial was performed under commercial feedlot conditions in western Canada to compare the efficacy of florfenicol and tilmicosin for the treatment of undifferentiated fever (UF) in calves that received metaphylactic tilmicosin upon arrival at the feedlot. One thousand and eighty recently weaned, auction market derived, crossbred beef calves suffering from UF were allocated to one of 2 experimental groups as follows: florfenicol, which was intramuscular (i.m.) florfenicol administered at the rate of 20 mg/kg body weight (BW) at the time of allocation (Day 0) and again 48 h later, or tilmicosin, which was subcutaneous (s.c.) tilmicosin administered once at the rate of 10 mg/kg BW on day 0. Five hundred and forty-four animals were allocated to the florfenicol group and 536 animals were allocated to the tilmicosin group. The chronicity, wastage, overall mortality, and bovine respiratory disease (BRD) mortality rates were significantly (P < 0.05) lower in the florfenicol group than in the tilmicosin group. There were no significant (P > or = 0.05) differences in first UF relapse, second UF relapse, hemophilosis mortality, or miscellaneous mortality rates between the florfenicol and tilmicosin groups. Average daily gain (ADG) from arrival at the feedlot to the time of implanting and ADG from allocation to the time of implanting were significantly (P < 0.05) lower in the florfenicol group as compared with the tilmicosin group. There were no significant (P > or = 0.05) differences in arrival weight, allocation weight, implanting weight, or ADG from arrival to allocation between the experimental groups. In the economic analysis, there was an advantage of $18.83 CDN per animal in the florfenicol group. The results of this study indicate that florfenicol is superior to tilmicosin for the treatment of UF because of lower chronicity, wastage, overall mortality, and BRD mortality rates. However, interpretation of these observations must take into consideration the fact that these calves received meta-phylactic tilmicosin upon arrival at the feedlot, which is a standard, cost-effective, management procedure utilized by feedlots in western Canada.     

Conglutinin and immunoconglutinin titers in stressed calves in a feedlot

OBJECTIVE: To determine whether increased conglutinin titers are evident in stressed calves that do not develop respiratory tract disease in feedlots, compared with respiratory tract disease, and to determine the increase in immunoconglutinin titers. ANIMALS: 101 mixed-breed beef calves. PROCEDURE: Calves were processed at 4 farms of origin and allowed to remain with their dams for another 100 days. Calves from each farm were brought to a centrally located order-buyer barn. In a feedlot, 101 calves were assigned to pens and observed daily for clinical signs of acute respiratory tract disease. When sick calves were detected, they were treated with antibiotics and isolated in a pen for 4 days. Conglutinin and immunoconglutinin titers were determined for all calves. RESULTS: During the 28-day study, 73 calves developed respiratory tract disease, whereas 28 calves remained healthy. Mean conglutinin titers differed significantly among calves from the 4 farms. Significant differences were not detected in conglutinin titers among calves on the basis of sex, morbidity, or vaccination status against Mannheimia haemolytica at each farm, the order-buyer barn, or the feedlot on days 8, 15, and 28 after arrival. Immunoconglutinin titers in calves differed significantly among farms and morbidity status. CONCLUSIONS AND CLINICAL RELEVANCE: Mean conglutinin titers in calves do not appear to be associated with the incidence of acute respiratory tract disease; however, increased immunoconglutinin titers appear to be associated with recovery of stressed calves from respiratory tract disease during the first 15 days after arrival in a feedlot.     

Efficacy of immunization of feedlot calves with a commercial Haemophilus somnus bacterin.

Two cohorts, consisting of 10,723 calves total, were identified in this prospective follow-up study to investigate whether immunization of auction market beef calves immediately upon arrival at the feedlot with a commercial Haemophilus somnus whole cell killed bacterin would reduce subsequent mortality. In addition to mortality rate, the use of incidence rate of fatal disease is introduced as an effect measure to examine vaccine efficacy in the feedlot. The Haemophilus somnus bacterin had no significant effect on the overall crude mortality rate; however, the bacterin appeared to significantly (p less than 0.05) reduce the incidence rate of fatal disease and the mortality rate during the first two months in the feedlot, when risk of fatal disease onset was highest. Once mortalities likely not associated with hemophilosis (for example, a fractured femoral neck) were removed from the analysis, steer mortality rate, but not heifer mortality rate, was reduced significantly (p less than 0.05) in the vaccinated group. The attributable percent overall for steers was 17.4%; this suggests that 17.4% of fatal respiratory disease in the unvaccinated steers could have been prevented by vaccination with the H. somnus bacterin. Heifer calves demonstrated a significantly (p less than 0.01) higher incidence rate of fatal disease during the first week than did steer calves, indicating that a different pattern of fatal disease existed for the two sexes. Use of a second vaccination two weeks after arrival did little to decrease mortality risk.     

The frequency, distribution and effects of antibodies, to seven putative respiratory pathogens, on respiratory disease and weight gain in feedlot calves in Ontario.

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.     

The effect of bovine viral diarrhea virus infections on health and performance of feedlot cattle

The aim of this study was to investigate the effect of bovine viral diarrhea virus (BVDV) infections (unapparent acute infections and persistent infections) on the overall health and performance of feedlot cattle. Calves from 25 pens (7132 calves) were enrolled in the study. Overall and infectious disease mortality rates were significantly higher (P < 0.05) in pens categorized at arrival as positive for type I BVDV and lower in pens that were positive for type II BVDV than in negative pens. Mortality attributed to BVDV infection or enteritis was significantly more common (P < 0.05) in the pens containing persistently infected (PI) calves than in pens not containing PI calves (non-PI pens). There were no statistically detectable (P > or = 0.05) differences in morbidity, overall mortality, average daily gain, or the dry matter intake to gain ratio between PI and non-PI pens. Although type-I BVDV infections in feedlots appear to contribute to higher mortality rates, the presence of PI calves alone does not appear to have a strong impact on pen-level animal health and feedlot performance.     

Some husbandry factors affecting mortality and morbidity on a calf-rearing unit

The influence of some husbandry factors on morbidity and mortality was studied in 1996 artificially reared, dairy bred calves over the period from purchase until about six weeks of age. The effects of housing (indoors versus outdoors), penning (individual versus group), breed, time since purchase and season of purchase were examined. The overall mortality rate was approximately 4 per cent and calves were more likely to die if reared in groups outdoors than if reared either singly or in groups indoors. The mortality rate was significantly lower in calves purchased between April and June than at other times of year. Pneumonia was the most common disease symptom (48.3 per cent of calves) with diarrhoea the second most common (14.1 per cent). Neither the type of penning nor housing affected the incidence of pneumonia but diarrhoea was most common in individually penned calves. Case mortality rates for diarrhoeic calves in group pens were higher than for those in single pens and case mortality rates for pneumonia were highest for calves reared in groups outdoors. More than half the cases of pneumonia occurred between one and three weeks after purchase whereas two-thirds of the cases of diarrhoea occurred within the first week after purchase. However, case mortality rates for both conditions appeared to increase with time since purchase.     

The association of titers to Haemophilus somnus, and other putative pathogens, with the occurrence of bovine respiratory disease and weight gain in feedlot calves.

Serum samples were obtained from 602 calves (from 19 groups in four feedlots: three in Ontario, and one in Alberta) upon arrival at the feedlot and 28 d later. Of these calves, 202 developed bovine respiratory disease (BRD) and 400 did not develop BRD. Based on high antibody titers noted upon arrival, we infer that most calves were exposed to Haemophilus somnus prior to arrival at the feedlot. Within a group, calves with high titers on arrival had a reduced risk of developing BRD later. Most calves did not experience titer increases after arrival; however, calves that had stable or increasing titers had a relatively low risk of contracting BRD. The calves at greatest risk of BRD were those with titers on arrival of less than 6.8 units and subsequent titer decreases of more than 1 unit. The effects of both the titer on arrival and the titer change after arrival were stable when the serologic effects of a number of viruses and Mycoplasma agents were considered. Neither antibody titer on arrival nor titer change was related to weight gain differences among calves. Calves with BRD or calves with lower weight on arrival had decreased weight gains in the first 28-day feeding period. The high titers on arrival may have protected most calves against further infection with H. somnus. However, since the calves that developed BRD had large titer increases to a number of viruses and to Pasteurella haemolytica, while having decreased antibody titers to H. somnus, we infer that the existing antibodies were "used up" in combatting the agents, including H. somnus, which may have "caused" the BRD. Calves which were able to increase their antibody levels to H. somnus tended to have a reduced risk of BRD.     

Some respiratory and enteric diseases of cattle: an update

Fibrinous pneumonia caused 40-45% of death losses in cattle shipped into Bruce County, Ontario. Feeding corn silage within the first 2 weeks of arrival increased mortality. Commingling cattle from different sources and keeping more than 110 cattle in a pen were detrimental. While use of antimicrobials in the starter ration was beneficial, prophylactic use of antimicrobials in the water was not. Mortality was directly proportional to morbidity and treatment costs. Vaccinating against any respiratory disease in the first 2 weeks after arrival was detrimental. Delaying vaccination for at least 2 weeks after arrival prevented the negative effects of vaccination in calves fed corn silage. Morbidity in cattle transported by train or truck did not differ. Bovine respiratory syncytial virus causes severe pulmonary edema-emphysema, with high morbidity and variable mortality, in confined calves in the fall and early winter. Death is usually from secondary bacterial pneumonia. Treatment involves use of pyrilamine maleate, dexamethasone and sulfamethazine. Salmonella muenster causes bloody diarrhea, abortion and death in cattle of any age. Treatment is with antibiotics selected by sensitivity tests. Cryptosporidium causes watery diarrhea in 1- to 2-week-old calves; infection is often fatal despite symptomatic treatment. Diagnosis is by identification of oocysts in fecal sugar flotation solution or May-Grünwald-Giemsa-stained fecal smears. Oral sulfamethazine has been used as a prophylactic.     

Antibody titers against bovine coronavirus and shedding of the virus via the respiratory tract in feedlot cattle

OBJECTIVE: To describe patterns of seroconversion to bovine coronavirus (BCV) and shedding of BCV from the respiratory tract in feedlot cattle. ANIMALS: 1,074 calves in feedlots in Ohio, Texas, and Nebraska. PROCEDURE: Nasal swab specimens were obtained at time of arrival (day 0) and at various times during the initial 28 days after arrival at feedlots. Specimens were tested for BCV, using an antigen-capture ELISA. Serum samples were obtained at time of arrival and again 28 days after arrival; sera were analyzed for antibodies to BCV, using an antibody-detection ELISA. RESULTS: Samples from 12 groups of cattle entering 7 feedlots during a 3-year period revealed that 78 of 1,074 (7.3%) cattle were shedding BCV (range, 0 to 35.9% within specific groups). At time of arrival, 508 of 814 (62.4%) cattle had low (< 50) or undetectable BCV antibody titers. Seroconversion to BCV during the initial 28 days after arrival was detected in 473 of 814 (58%) cattle tested (range, 20.3 to 84.1 % within specific groups). In cattle shedding BCV from the nasal passages, 49 of 68 (72.1 %) seroconverted, and 472 of 746 (63.3%) cattle that were not shedding the virus seroconverted. CONCLUSIONS AND CLINICAL RELEVANCE: Bovine coronavirus can be detected in populations of feedlot cattle in the form of viral shedding as well as seroconversion to the virus. Although only a few cattle were shedding the virus at the time of arrival at a feedlot, most of the cattle seroconverted to BCV by 28 days after arrival.     

Abortion and Calf Mortality in Danish Cattle Herds

The aetiology of abortions and calf mortality in 65 Danish cattle herds consisting of both dairy and beef breeds during a 1-year period is described. All observed aborted foetuses, stillborn calves, and calves dying before 6 months of age were necropsied, and relevant microbiological examinations were performed. A total of 240 calves and 66 abortions were submitted corresponding to a calf mortality rate of 7%. The abortion frequency could not be calculated. 43% of the calves died at day 0, while 22% were aborted, 15% died during the first week of life, 9% died from 1 to 4 weeks of age, and 11% died at the age of 1 to 6 months. The most common cause was neonatal pulmonic atelectasis (stillbirth) followed by foetal infections, pneumonia, and septicaemia.     

The pattern of fatal fibrinous pneumonia (shipping fever) affecting calves in a large feedlot in Alberta (1985-1988).

Data from a retrospective field study were used to describe the epidemiology of fatal fibrinous pneumonia as it affected beef calves entering a large commercial feedlot in southwestern Alberta during the fall months of y 1985 to 1988. A chute-side computer system was used to record processing and health data on 58885 calves during this period. The large annual variation (10%-57%) in the proportion of total mortality due to fibrinous pneumonia indicated that crude mortality cannot be used in epidemiological studies as a surrogate measure of fibrinous pneumonia mortality. Yearly epidemic curves for fatal fibrinous pneumonia were very similar, with a short time interval (median, 19-22 d) between arrival and fatal disease. Fully 75% of the calves that died of fibrinous pneumonia already were sick within 2 weeks of arrival. Studies of the biological, environmental, and population factors that are present before and shortly after arrival at the feedlot are needed to identify strategies for reducing the incidence of fatal fibrinous pneumonia.     

Association between infection of the respiratory tract attributable to bovine coronavirus and health and growth performance of cattle in feedlots

OBJECTIVE: To determine the association between respiratory tract infection with bovine coronavirus (BCV), treatment for respiratory tract disease, pulmonary lesions at slaughter, and average daily gain in cattle in feedlots. ANIMALS: 837 calves in feedlots in Ohio and Texas. PROCEDURE: Nasal swab specimens were obtained from cattle at arrival in a feedlot (day 0) and at various times during the initial 28 days after arrival. Specimens were tested for BCV, using an antigen-capture ELISA. Serum samples were obtained at arrival and again 28 days after arrival and tested for antibodies to BCV, using an antibody-detection ELISA. Information was collected regarding treatment for cattle with respiratory tract disease and average daily gain during the feeding period. Pulmonary lesions were evaluated at slaughter. RESULTS: Cattle shedding BCV from the nasal cavity and developing an antibody response against BCV were 1.6 times more likely to require treatment for respiratory tract disease than cattle that did not shed the virus or develop an immune response against BCV. Additionally, cattle that shed BCV from the nasal cavity were 2.2 times more likely to have pulmonary lesions at slaughter than cattle that did not shed the virus. The BCV shedding or seroconversion status did not affect average daily gain. CONCLUSIONS AND CLINICAL RELEVANCE: Bovine coronavirus infects feedlot cattle and is associated with an increased risk for cattle developing respiratory tract disease and pulmonary lesions. Development of appropriate control measures could help reduce the incidence of respiratory tract disease.     

Descriptive epidemiology of morbidity and mortality in Minnesota dairy heifer calves

A prospective study was carried out on 845 heifer calves born during 1991 on 30 Holstein dairy farms in southeast Minnesota. The objectives of the study were to describe the epidemiology of morbidity and mortality in dairy calves from birth to 16 weeks of age (with an emphasis on respiratory disease), to examine individual calf and herd management practices as risk factors for calf morbidity and mortality, and to validate producer diagnosis of mortality. Incidence rates for all morbidity, enteritis, and pneumonia were 0.20, 0.15, and 0.10 cases per 100 calf-days at risk for the period of the study. Risk of enteritis was highest in the first 3 weeks of life, with pneumonia risk highest at 10 weeks of age. Case fatality rates averaged 11.8%, 17.9%, and 9.4% for all diagnoses, enteritis, and pneumonia, respectively. Average daily rates of gain from birth to 16 weeks of age differed between farms that had inadequate calf housing (0.8 kg day⁻¹) versus those with adequate calf housing (1.0 kg day⁻¹). Approximately half of the calves in the cohort (418) had blood samples taken monthly from birth until 16 weeks of age. Of the calves sampled, only 19 calves showed a four-fold rise in serum titers to respiratory viruses. Sixteen calves seroconverted to BVDV, two calves to IBRV, and one calf to PI3 virus. Of 98 calves less than 10 days of age tested for adequacy of passive transfer, 35 (35.7%) had serum immunoglobulin levels of less than 800 mg dl⁻¹. There were no significant differences in mortality or morbidity between calves that had adequate passive transfer and those that did not. The incidence of mortality was 0.08 deaths per 100 calf-days at risk; 64 calves died during the 16 months of the study. The risk of death was highest at 2 weeks of age. Enteritis was the most common cause of death (28 deaths, 44% of all deaths) followed by pneumonia (19 deaths, 30% of all deaths). Comparing producer diagnosis of mortality with necropsy results yielded sensitivities of 58.3% and 56% and specificities of 93% and 100% for producer diagnoses of enteritis and pneumonia, respectively. The kappa statistic comparing producer diagnosis with necropsy result was 0.47. The most common pathogens isolated from calves that died of enteritis were rotavirus (five calves), and Escherichia coli (four calves). Pathogens isolated from pneumonic lungs included Pasteurella multocida (three calves), Haemophilus somnus (three calves), and Pasteurella haemolytica (one calf).     

Associations between weather conditions during the first 45 days after feedlot arrival and daily respiratory disease risks in autumn-placed feeder cattle in the United States

Data on associations between weather conditions and bovine respiratory disease (BRD) morbidity in autumn-placed feedlot cattle are sparse. The goal of our study was to quantify how different weather variables during corresponding lag periods (considering up to 7 d before the day of disease measure) were associated with daily BRD incidence during the first 45 d of the feeding period based on a post hoc analysis of existing feedlot operational data. Our study population included 1,904 cohorts of feeder cattle (representing 288,388 total cattle) that arrived to 9 US commercial feedlots during September to November in 2005 to 2007. There were 24,947 total cases of initial respiratory disease (animals diagnosed by the feedlots with BRD and subsequently treated with an antimicrobial). The mean number of BRD cases during the study period (the first 45 d after arrival) was 0.3 cases per day per cohort (range = 0 to 53.0), and cumulative BRD incidence risks ranged from 0 to 36% within cattle cohorts. Data were analyzed with a multivariable mixed-effects binomial regression model. Results indicate that several weather factors (maximum wind speed, mean wind chill temperature, and temperature change in different lag periods) were significantly (P < 0.05) associated with increased daily BRD incidence, but their effects depended on several cattle demographic factors (month of arrival, BRD risk code, BW class, and cohort size). In addition, month and year of arrival, sex of the cohort, days on feed, mean BW of the cohort at entry, predicted BRD risk designation of the cohort (high or low risk), cohort size, and the interaction between BRD risk code and arrival year were significantly (P < 0.05) associated with daily BRD incidence. Our results demonstrate that weather conditions are significantly associated with BRD risk in populations of feedlot cattle. Defining these conditions for specific cattle populations may enable cattle health managers to predict and potentially manage these effects more effectively; further, estimates of effects may contribute to the development of quantitative predictive models for this important disease syndrome.     

The association between serological evidence of mycoplasma infection and respiratory disease in feedlot calves.

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.     

Transmission of bovine coronavirus and serologic responses in feedlot calves under field conditions

OBJECTIVE: To compare shedding patterns and serologic responses to bovine coronavirus (BCV) in feedlot calves shipped from a single ranch in New Mexico (NM calves) versus calves assembled from local sale barns in Arkansas (AR calves) and to evaluate the role of BCV on disease and performance. ANIMALS: 103 feedlot calves from New Mexico and 100 from Arkansas. PROCEDURES: Calves were studied from before shipping to 35 days after arrival at the feedlot. Nasal swab specimens, fecal samples, and serum samples were obtained before shipping, at arrival, and periodically thereafter. Bovine coronavirus antigen and antibodies were detected by use of an ELISA. RESULTS: NM calves had a high geometric mean titer for BCV antibody at arrival (GMT, 1,928); only 2% shed BCV in nasal secretions and 1% in feces. In contrast, AR calves had low antibody titers against BCV at arrival (GMT, 102) and 64% shed BCV in nasal secretions and 65% in feces. Detection of BCV in nasal secretions preceded detection in feces before shipping AR calves, but at arrival, 73% of AR calves were shedding BCV in nasal secretions and feces. Bovine coronavirus infection was significantly associated with respiratory tract disease and decreased growth performance in AR calves. CONCLUSIONS AND CLINICAL RELEVANCE: Replication and shedding of BCV may start in the upper respiratory tract and spread to the gastrointestinal tract. Vaccination of calves against BCV before shipping to feedlots may provide protection against BCV infection and its effects with other pathogens in the induction of respiratory tract disease.     

The relationship of hematology and serum chemistry parameters to treatment for respiratory disease and weight gain in Ontario feedlot calves.

In the fall of 1983, 322 western calves, in five different groups, were bled on arrival at two Ontario feedlots. Calves receiving treatment for respiratory disease, within 35 days of arrival, were denoted as cases. The hematology and serum chemistry parameters of cases were compared to those of controls. Cases had significantly (p less than 0.05) lower hematocrits, fewer platelets, and more band cells on arrival, than did controls. Cases also had lower serum phosphorous, magnesium, potassium, iron and alkaline phosphatase levels, and increased bilirubin and aspartate aminotransferase levels relative to controls. Based on the results of multivariable logistic regression, hematocrit, platelet numbers, serum phosphorous, iron and aspartate aminotransferase levels were the most significant parameters for the prediction of respiratory disease. Reference values for stressed feedlot calves were created. Most parameters were distributed in an approximately normal manner, however the group to group variation in most parameters was significant.