Effect of calf age and Salmonella bacterin type on ability to produce immunoglobulins directed against Salmonella whole cells or lipopolysaccharide.

A commercially available Salmonella bacterin was administered to Holstein calves starting at 1 to 19 weeks of age. Serum samples were obtained before administering bacterin and at 2-week intervals thereafter. An ELISA with Salmonella dublin lipopolysaccharide (LPS) or S dublin whole cells as antigen, was used to measure specific IgG and IgM responses. Antibody responses to LPS were not detected from calves < 12 weeks old inoculated with killed bacterin. Immunoglobulin responses to whole-cell antigen were detected from all age groups of calves inoculated with the same killed Salmonella bacterin. Calves < 11 weeks old are able to produce immunoglobulins to some whole-cell antigens, but are unable to produce anti-LPS immunoglobulins when inoculated with killed Salmonella bacterin. This age-related response to killed Salmonella antigens may account, in part, for increased susceptibility to salmonellosis in calves < 12 weeks old. In comparison to the response for killed antigen, 8 calves given modified-live aromatic-dependent S dublin bacterin at 1 to 3 weeks of age had detectable anti-LPS immunoglobulins after immunization, although the response was not as rapid and was of a lesser magnitude than that of older calves given killed Salmonella bacterin.     

Vaccination of calves against Salmonella dublin with aromatic-dependent Salmonella typhimurium

Ten Holstein calves were divided into 2 groups. Five calves served as nonvaccinated controls, and 5 calves were vaccinated IM at 2 and 3 weeks of age with 10(9) aromatic-dependent (aro-) Salmonella typhimurium strain SL1479 containing O antigens 1, 4, 12. Serious adverse reactions to vaccination were not observed in the calves. Mean maximum rectal temperature increase in the vaccinated calves was 1.5 C. One calf had diarrhea and depressed appetite for 1 day after vaccination. At 5 weeks of age, all calves were challenge exposed orally with 1.5 X 10(11) virulent S dublin strain SL1367 (O antigens 9,12). After challenge-exposure inoculum was given, 1 of 5 vaccinated calves died and 4 of the 5 nonvaccinated calves died (P less than 0.05). Thus, some cross serotype protection against S dublin was induced by parenteral vaccination of calves with aro- S typhimurium strain SL1479, although protection was not complete.     

Efficacy of a streptomycin-dependent, live Pasteurella haemolytica vaccine against challenge exposure to Pasteurella haemolytica in cattle

A streptomycin-dependent, live Pasteurella haemolytica vaccine was given in 1 or 2 doses to 2 groups of weaned calves; 2 other groups of calves were not vaccinated. All calves in the vaccinated groups and calves in 1 of the nonvaccinated groups were stressed by transport, intratracheally inoculated with bovine herpesvirus type-1 (Cooper strain), and then intratracheally inoculated with P haemolytica type A1. The 4th group of calves (nonvaccinated controls) was not stressed and were not intratracheally inoculated with virus or bacteria. Mean daily weight gains, total clinical sign scores, lung lesion scores, plasma fibrinogen concentrations, and antibody titers against P haemolytica were determined at various intervals. Calves that had been vaccinated twice had greater mean daily weight gains and lower total clinical sign scores and lung lesion scores than did nonvaccinated, challenge-exposed calves, but the difference was not significant (P greater than 0.05). Calves vaccinated once had the greatest mean daily weight gains, the lowest total clinical sign scores, and the lowest lung lesion scores when compared with the other 2 challenge-exposed groups of calves. Mean daily weight gains and total clinical sign scores of calves vaccinated once were significantly different (P less than 0.05) than those of calves vaccinated twice. Nonvaccinated, nonchallenge-exposed control calves did not develop clinical signs of disease, did not develop lung lesions, and had consistently positive daily weight gains, and had scores in these areas that were significantly different (P less than 0.05) from those of all challenge-exposed groups of calves. Increases in plasma fibrinogen concentrations corresponded to infection with P haemolytica.(ABSTRACT TRUNCATED AT 250 WORDS)     

Infection and immune kinetics of Trichostrongylus axei in calves.

In one experiment, 21 calves were given daily oral immunizing inoculations of 1,000 infective larvae (L3) of Trichostrongylus axei, an abomasal nematode parasites, for 35 weeks. Calves were euthanatized in groups of three every 5 weeks to determine infection kinetics. Worm populations steadily increased through week 30, but the percentage of total inoculum that became established was about the same through week 30. At week 35, the number of worms dropped markedly. In a second experiment, 27 calves given daily oral inoculations of infective larvae were allotted to three groups comprised of three subgroups each: (A), challenge-exposed vaccinated; (B), nonchallenge-exposed vaccinated; and (C), challenge-exposed nonvaccinated. Calves of subgroups A and C were given single challenge inoculums of 200,000 L3 after the 10th, 20th, and 30th weeks. All calves were necropsied 35 days after challenge exposure. When immunity was determined from the equation: [(No. of worms in [(B + C)-A])/No. of worms in [B + C])] X 100, immunity was 35% at 10 weeks, 52% at 20 weeks, and 100% at 30 weeks.     

Nutritional and pathophysiologic effects of clinically apparent and subclinical infections of Ostertagia ostertagi in calves.

Nutritional and physiologic effects of clinically apparent and subclinical Ostertagia ostertagi infections were studied in 3 groups of 5 calves each. Group-1 calves were inoculated with 100,000 Ostertagia ostertagi third-stage larvae (L3)/calf/wk for 14 weeks. Group-2 calves were inoculated with 10,000 L3/calf/wk for 14 weeks, and group-3 calves were no inoculated. Calves in group 1 had decreased dry matter intake and feed utilization from 4 weeks after initial inoculation. Group-2 calves had no changes in dry matter intake, but had decreased feed utilization at 12 and 14 weeks. Calves with clinically apparent infections (group 1) lost a mean weight of 11.8 kg, whereas calves with suclinical infections (group 2) lost a mean of 46.6 kg, and control calves lost a mean of 60.7 kg. Calves with O ostertagi infections (group 1 and 2) also had decreased carcass quality at slaughtering, which was reflected in decreased dressing weights and increased water-holding capacity of the rib-eye muscle. Calves in groups 1 and 2 also had lower carcass yield and rib-eye muscle weight, and group-1 calves had decreased protein content. Results of hematologic, pathologic, parasitologic, and clinical examinations mirrored nutritional changes.     

A field trial of preshipment vaccination of calves

A field trial to investigate the efficacy of vitamins ADE, a Haemophilus somnus bacterin, a pasteurella bacterin, and two intranasal infectious bovine rhinotracheitis-parainfluenza type 3 vaccines administered to beef calves at least three weeks prior to weaning and shipment was conducted.

Over 1000 calves were vaccinated, but of the 692 calves shipped from the ranch of origin, only 276 calves were located in Ontario, or Quebec, feedlots. The average treatment rate was 30%. Neither vitamins ADE, H. somnus bacterin, pasteurella bacterin or the porcine tissue culture infectious bovine rhinotracheitis-parainfluenza type 3 vaccine had a significant effect on treatment rates for respiratory disease. Calves vaccinated with the temperature sensitive infectious bovine rhinotracheitis-parainfluenza type 3 vaccine had a significantly (p < 0.05) lower treatment rate than the nonvaccinated, and the porcine tissue culture infectious bovine rhinotracheitis-parainfluenza type 3 vaccinated, calves. Calves vaccinated with the temperature sensitive infectious bovine rhinotracheitis-parainfluenza type 3 vaccine did not have a significantly reduced treatment rate in comparison to nonvaccinated calves from the same source.

     

Duration of immunity and efficacy of an oil emulsion Escherichia coli bacterin in cattle

An oil emulsion Escherichia coli bacterin administered in 1- and 2-dose vaccination regimens was evaluated in beef cattle. Serologic responses to the K99 pilus antigen were monitored, and suckling offspring from vaccinated and nonvaccinated cows were inoculated with virulent, K99-positive, enterotoxigenic Escherichia coli. The degree of protection and duration of immunity conferred were determined in 2 respective studies. In the first study (study A), titers of pregnant cattle were determined from time of vaccination through calving (a 6- to 20-week period). Titers of 24 cows vaccinated with a single 2-ml dose of bacterin were compared with those of 24 cows given a 2-dose regimen and with those of 23 nonvaccinated cattle (contemporary controls). Inoculum consisting of 1.2 X 10(12) viable enterotoxigenic E coli/dose administered to nursing calves from these dams yielded 0% mortality (0 deaths/20 calves) in calves from 1-dose vaccinates, 6% mortality (1 death/18 calves) in calves from 2-dose vaccinates, and 37% mortality (7 deaths/19 calves) in calves from nonvaccinated dams. Study B was an extended evaluation conducted in cattle that were kept in the study up to 87 weeks from initial vaccination until calving. Serologic titers to the K99 pilus antigen were compared in 1-dose, 2-dose, and nonvaccinated cattle in groups of 8, 6, and 6, respectively. Calves from these dams were inoculated with 8.1 X 10(11) viable enterotoxigenic E coli/dose, which resulted in 0% mortality (0 deaths/5 calves) in calves from 1-dose vaccinates, 0% mortality (0 deaths/5 calves) in calves from 2-dose vaccinates, and 80% mortality (5 deaths/6 calves) in calves from nonvaccinated dams.     

Evaluation of an autogenous Salmonella bacterin and a modified live Salmonella serotype Choleraesuis vaccine on a commercial dairy farm.

OBJECTIVE: To compare the efficacy of a Salmonella bacterin and a modified live Salmonella ser. Choleraesuis vaccine on a commercial dairy. ANIMALS: 450 cows in late gestation and 80 calves. PROCEDURE: Group-1 cows (n = 150) were vaccinated once with a modified live S. Choleraesuis (serogroup C1) strain 54 (SC54) vaccine, group-2 cows (150) were vaccinated on enrollment and 30 days later with a Salmonella ser. Montevideo (serogroup C1) bacterin, and group-3 cows (150) served as unvaccinated controls. One gallon of colostrum harvested from the first 80 cows to calve was fed to each calf. Outcome assessments included fecal shedding of Salmonella spp for the first 10 days after parturition (cows) or birth (calves), milk production, involuntary culling rate, mastitis incidence, antimicrobial use, and mortality rate. RESULTS: Salmonellae were isolated from 306 of 309 (99%) cows and 64 of 74 (86.5%) calves. Shedding frequency was less in SC54-vaccinated cows and calves that received colostrum from those cows, compared with the other groups, and vaccination was specifically associated with less shedding of serogroup C1 salmonellae. Production data were similar among groups. CONCLUSIONS AND CLINICAL RELEVANCE: Vaccination of pregnant cows with an autogenous Salmonella bacterin had no effect on fecal shedding of salmonellae, whereas vaccination with a modified live S. Choleraesuis vaccine reduced the frequency of fecal shedding of serogroup C1 salmonellae during the peripartum period. A commercial S. Choleraesuis vaccine licensed for use in swine may be more efficacious than autogenous Salmonella bacterins on dairies infected with serogroup C1 salmonellae.     

Efficacy of an experimental BHV-1 subunit gIV vaccine in beef calves challenged with BHV-1 in aerosol.

Thirty-six beef calves were used to test the efficacy of an experimental truncated BHV-1 glycoprotein (tgIV) vaccine. Calves from 1 source and +/- 1 mo of age were randomly divided into 4 groups: 1) control (adjuvant VSA3), 2) vaccinated with tgIV at 3 and 4 mo of age, 3) vaccinated with tgIV at 3 and 7 mo of age, or 4) vaccinated with tgIV at 6 and 7 mo of age. Calves were challenged with BHV-1 in aerosol (strain 108) at 7 1/2 mo of age. Prior to challenge, serum neutralizing (SN) antibody titers to BHV-1 were significantly (P < 0.05) higher in all vaccinated calves than in controls. Calves vaccinated at 3 and 7, or 6 and 7, mo of age had significantly (P < 0.05) higher SN antibody and nasal antibody titers to BHV-1 and ELISA (enzyme linked immunosorbent assay) titers to gIV at prechallenge than those vaccinated at 3 and 4 mo of age or controls. Postchallenge nasal shedding of BHV-1 occurred only in controls and those vaccinated at 3 and 4 mo of age. Control calves lost significantly (P < 0.05) more weight and had higher sick scores after challenge than those vaccinated at 3 and 7, or at 6 and 7, mo of age. There were strong correlations (P < 0.001) between antibody titers, virus shedding, and sickness.     

Aromatic-dependent Salmonella dublin as a parenteral modified live vaccine for calves

A virulent Salmonella dublin isolate was made histidine-requiring (his-) to allow recognition. The his- derivative, SL1367 (still calf-virulent), was then given by transduction and mutation, a transposon-generated non-reverting aromatic biosynthesis (aro) defect; this defect caused loss of virulence for the mouse. The his- aro- derivative strain, SL1438, was effective as a live vaccine in mice. Twenty male Holstein calves were divided into 4 groups. Groups I, II, and III were vaccinated IM at 2 weeks and at 3 weeks of age with aromatic-dependent (aro-) S dublin strain SL1438. Groups I and III received freshly prepared vaccine and group II received lyophilized vaccine. Serious adverse reactions to the vaccination were not seen. After vaccination, the mean maximum increase in rectal temperature was 1.8 C in group I and III calves and 0.6 C in group II calves. Fewer group II calves developed diarrhea (1 of 5) or positive blood cultures (0 of 5) after vaccination compared with group I and III calves (6 of 10 and 5 of 10, respectively). Postvaccination diarrhea was mild and of short duration. Group IV was comprised of 5 nonvaccinated calves. At 5 weeks of age, all calves were challenge exposed orally. Group I, II, and IV calves were challenge exposed with 10(11) virulent S dublin SL1367. Group III was challenge exposed with 10(11) virulent S typhimurium UCD 108-11. Subsequently, fever and diarrhea (lasting 1 to 3 days), but no deaths, were observed in the vaccinated calves. Four of the 5 nonvaccinated (group IV) calves died (P less than 0.001) within 8 days after challenge exposure. Aro- S dublin SL 1438 did not cause serious adverse effects and provided protection against oral challenge exposure with either virulent S dublin or S typhimurium.     

Immunologic response to Pasteurella haemolytica and resistance against experimental bovine pneumonic pasteurellosis, induced by bacterins in oil adjuvants

Immunogenicity of and protection afforded by Pasteurella haemolytica bacterins were studied in calves. Bacterins contained an aluminum hydroxide in gel (ALH) adjuvant or one of the following oil-in-water adjuvants: Freund's complete adjuvant (FCA), Freund's incomplete adjuvant (FIA), and trehalose dimycolate (TDM). On days 0 and 7, calves were vaccinated with phosphate-buffered saline solution (PBSS), a bacterin, or live P haemolytica. Transthoracic intrapulmonic challenge exposure was done on day 21. In 3 experiments, there were no significant (P greater than 0.05) differences between lung lesions induced in PBSS-or ALH bacterin-vaccinated calves. Both FCA and FIA bacterins significantly (P less than 0.05) enhanced resistance against challenge exposure. Resistance induced by FCA and FIA bacterins was comparable with that induced by vaccination with live P haemolytica. Calves vaccinated with FIA bacterin and challenge-exposed to P haemolytica at a concentration of 4.5 X 10(9) colony-forming units (4.5 times greater than used in the first 3 experiments) resisted challenge exposure similar to calves given live organisms. The TDM bacterin failed to enhance resistance. All bacterins caused a significant increase (P less than 0.05) in serum antibody to P haemolytica somatic antigens, as measured by a quantitative fluorometric immunoassay. Pasteurella haemolytica leukotoxin neutralizing antibody titers did not increase significantly (P greater than 0.05) in sera after vaccination with any bacterin. Vaccination with FCA and FIA bacterins resulted in a significant increase (P less than 0.001) in serum antibody to a carbohydrate-protein subunit of P haemolytica, as measured by an enzyme-linked immunosorbent assay.(ABSTRACT TRUNCATED AT 250 WORDS)     

The influence of maternal antibody and age of calves on effective vaccination against Leptospira interrogans serovar hardjo

Twelve seronegative cows were vaccinated with an experimental bivalent Leptospira interrogans serovars hardjo and pomona vaccine late in their first pregnancy. Calves born of these dams were divided into 4 equal groups that received this vaccine at 4, 6, 10 and 18 weeks of age, respectively. Before vaccination the group geometric mean titres of maternally-derived circulating antibodies ranged from 2 to 25 for the microscopic agglutination (MA) test and 3 to 35 for enzyme-linked immunosorbent assay (ELISA) using a serovar hardjo outer envelope antigen. Post-vaccination peak titres were 645 to 1612 for MA and 562 to 1037 for ELISA, respectively. Calves vaccinated at the youngest age, had the highest pre-vaccination circulating maternal antibody titres, but showed the smallest rise in post-vaccination antibody titres. Circulating maternal antibody was detected in calves up to 13 weeks of age. All immunised calves were protected against a virulent challenge with serovar hardjo type Hardjobovis, regardless of their age or maternally-derived antibody titres. These findings indicate that calves as young as 4 weeks old, vaccinated in the presence of maternally-derived antibody, can be fully protected against homologous virulent challenge.     

Effects of vaccination of calves against induced Haemophilus somnus pneumonia

The efficacy of a killed whole-cell Haemophilus somnus bacterin against induced H somnus pneumonia was examined in 10-week-old male calves. Twenty calves were assigned to 1 of the 3 following groups: group 1, nonvaccinated controls (n = 4); group 2, vaccinated once (n = 8); and group 3, vaccinated twice 14 days apart (n = 8). The serum antibody response to vaccination and challenge exposure was evaluated by the bacterial agglutination test and solid-phase immunoassay (SPIA). Vaccinating calves twice, 14 days apart, significantly (P less than 0.05) reduced the severity of clinical signs of pneumonia and gross lesions. Deaths occurred in 1 of 4 nonvaccinated controls, 1 calf vaccinated once, and none of the calves vaccinated twice, 14 days apart. Postvaccination bacterial agglutination titers measured 14 days after the final vaccination were not significantly different between groups 2 and 3, but SPIA titers were significantly (P less than 0.05) higher in groups 2 and 3, compared with those in group 1. The less severe clinical signs of pneumonia observed in group-3 calves, compared with those in calves in groups 1 and 2, were significantly (P less than 0.01) correlated to higher SPIA titers, indicating the protective value of vaccinating twice.     

Vaccination of calves with a diaminopimelic acid mutant of Salmonella typhimurium.

The purpose of this study was to evaluate the safety and efficacy of a diaminopimelic acid mutant of Salmonella typhimurium as a vaccine for calves. Transposon techniques were used to create a stable nonreverting diaminopimelic acid mutant of a virulent S. typhimurium strain. Calves were vaccinated at weekly intervals with the diaminopimelic acid mutant given as an oral dose of 10(10) organisms, followed by two subcutaneous doses of 10(9) organisms. The calves tolerated vaccination well and the vaccine strain was eliminated from the feces within four days. Of five vaccinated calves, three survived challenge with 5 X 10(9) organisms of the parent strain whereas all five unvaccinated calves that were challenged died. The surviving calves eliminated the challenge organism from the feces within three weeks.     

Effects of various vaccination protocols on passive and active immunity to Pasteurella haemolytica and Haemophilus somnus in beef calves.

Two field trials were conducted in a beef cow herd in Saskatchewan to determine the effectiveness of a combined Pasteurella haemolytica and Haemophilus somnus vaccine in increasing passively and actively acquired antibodies in beef calves. Vaccination of dams at 4 and/or 7 weeks prepartum was associated with increased antibody titers to P. haemolytica and H. somnus in their serum (P < 0.05), colostrum (P < 0.05), and serum of their calves at 3 days and 1 month of age (P < 0.05). There was no significant (P > 0.05) difference in antibody titers in the colostrum and serum of calves from single or double vaccinated dams. Calves vaccinated at 1 and 2 months of age in the face of maternal antibodies to P. haemolytica and H. somnus had significantly (P < 0.05) higher antibodies to P. haemolytica and H. somnus at 4 and 6 months of age than did unvaccinated calves. Calves vaccinated at 3 and 4 months of age in the face of low levels of preexisting antibodies had significantly (P < 0.05) higher antibodies to P. haemolytica at 5 months of age and to H. somnus at 5 and 6 months of age than did unvaccinated calves. Calves vaccinated once at 4 months of age had significantly (P < 0.05) higher antibody titers to P. haemolytica and H. somnus at 4.5 months of age than did unvaccinated calves, but this difference was not apparent at 6 months of age.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum antibodies to Pasteurella haemolytica lipopolysaccharide: relationship to experimental bovine pneumonic pasteurellosis

An enzyme-linked immunosorbent assay was used to determine the serum antibody response to Pasteurella haemolytica lipopolysaccharide (LPS) for calves vaccinated with saline solution, a formalin-killed P haemolytica bacterin, or live P haemolytica. Bacterin-vaccinated calves had a lower antibody response to LPS than did calves vaccinated with live P haemolytica. Calves vaccinated with either saline solution or the bacterin were more susceptible to intrapulmonic challenge exposure with P haemolytica than were calves vaccinated with liver organisms. Serum antibody responses to P haemolytica LPS did not seem important for resistance to challenge exposure, because there was no significant correlation (P greater than 0.05) between the lung lesion score and antibody response to P haemolytica LPS. There was a highly significant correlation (P less than 0.001) between antibody detected against P haemolytica LPS and that against formalin-killed P haemolytica. Competitive binding studies indicated that P haemolytica LPS is a major antigenic determinant on the surface of P haemolytica. There did not seem to be substantial cross-reaction between LPS from P haemolytica and that from Escherichia coli (serotype O26:B6).     

Correlation of macrophage migration-inhibition factor and protection from challenge exposure in calves vaccinated with Salmonella typhimurium

Migration of bovine macrophages under agarose was used to assess cellular immunity in 7 nonvaccinated calves and 9 calves vaccinated with Salmonella typhimurium. The 9 vaccinated calves were allotted to 4 groups. Group I calves were vaccinated twice orally with small doses of virulent S typhimurium; group II calves were vaccinated twice orally with genetically altered aromatic-dependent (aro-) S typhimurium SL3261; group III calves were vaccinated twice IM with small doses of virulent S typhimurium; and group IV calves were vaccinated twice IM with aro- S typhimurium SL1479. Samples of blood were obtained from these calves at 2 weeks after the 2nd vaccinal dose was given, and lymphocytes were harvested, using lymphocyte separation medium. Lymphocytes in serum-free medium were then incubated with S typhimurim antigen for 48 hours. Lymphocytes were then transferred to antigen-free medium and incubated for 48 hours, and the supernatant was assayed for the migration-inhibition factor (MIF). Lymphocyte supernatant was assayed for MIF by incubating it for 48 hours with 2.0 X 10(4) alveolar macrophages in agar wells. The macrophage migration distance was measured and compared with control values. Macrophage migration was inhibited in the presence of supernatant of lymphocytes from vaccinated calves that had been incubated with antigen, indicating the presence of the MIF in the supernatant. Migration distances, as a percentage of control, were 33% for group I calves (oral vaccination, virulent vaccinal organism), 60% for group II calves (oral vaccination, aro- vaccinal organism), 41% for group III (IM vaccination, virulent organism), and 25% for group IV (IM vaccination, aro- vaccinal organism).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of flunixin meglumine on Escherichia coli heat-stable enterotoxin-induced diarrhea in calves

In a study to evaluate the effect of flunixin meglumine on secretory diarrhea, 11 calves were assigned to 3 groups: group 1 (n = 3) served as controls, group-2 calves (n = 4) were given 2.2 mg of flunixin meglumine/kg, IM at 7 AM and 3 PM, and group-3 calves (n = 4) were given 2.2 mg of flunixin meglumine/kg, IM at 7 AM, 11 AM, and 3 PM. All calves were given approximately 200 micrograms of heat-stable Escherichia coli enterotoxin (STa) orally at 8 AM. Mean cumulative fecal output for groups 1, 2, and 3 was 1,331.0 +/- 317.2 g, 1,544.3 +/- 154.4 g, and 785.5 +/- 276.5 g, respectively. There was a significant (P less than 0.05) reduction in mean fecal output in group-3 calves, compared with that in groups 1 and 2. Calves in group 2 tended to have a delay, but not a reduction, in their fecal output. At 12 hours, hemoconcentration was significantly (P less than 0.05) greater in group-1 calves than in group-2 or group-3 calves.     

Evaluation of protection against virulent bovine viral diarrhea virus type 2 in calves that had maternal antibodies and were vaccinated with a modified-live vaccine

OBJECTIVE: To evaluate the efficacy of an adjuvanted modified-live bovine viral diarrhea virus (BVDV) vaccine against challenge with a virulent type 2 BVDV strain in calves with or without maternal antibodies against the virus. DESIGN: Challenge study. ANIMALS: 23 crossbred dairy calves. PROCEDURES: Calves were fed colostrum containing antibodies against BVDV or colostrum without anti-BVDV antibodies within 6 hours of birth and again 8 to 12 hours after the first feeding. Calves were vaccinated with a commercial modified-live virus combination vaccine or a sham vaccine at approximately 5 weeks of age and challenged with virulent type 2 BVDV 3.5 months after vaccination. Clinical signs of BVDV infection, development of viremia, and variation in WBC counts were recorded for 14 days after challenge exposure. RESULTS: Calves that received colostrum free of anti-BVDV antibodies and were vaccinated with the sham vaccine developed severe disease (4 of the 7 calves died or were euthanatized). Calves that received colostrum free of anti-BVDV antibodies and were vaccinated and calves that received colostrum with anti-BVDV antibodies and were vaccinated developed only mild or no clinical signs of disease. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that the modified-live virus vaccine induced a strong protective immune response in young calves, even when plasma concentrations of maternal antibody were high. In addition, all vaccinated calves were protected against viral shedding, whereas control calves vaccinated with the sham vaccine shed virus for an extended period of time.     

Study of an attenuated Anaplasma marginale vaccine in Mexico natural challenge of immunity in an enzootic area.

An evaluation was made of the protection induced by an attenuated Anaplasma marginale vaccine in young purebred cattle against the challenge exposure of naturally transmitted anaplasmosis in enzootic areas of Mexico. The cattle, which were raised in isolation units free of arthropods, consisted of 10 Brown Swiss calves (1 to 13 months of age) and 8 Holstein calves (5 to 7 months of age). They were paired by breed, age, and body weight, and allotted to 2 equal groups. Calves in 1 group were vaccinated, and at 6 weeks after vaccinations were done, calves in both groups were placed in the field where they were raised for approximately 1 year. Two Holstein and 3 Brown Swiss calves of the nonvaccinated group (group 2) developed clinical anaplasmosis, and the remaining calves of this group had hematologic evidence of the disease during the 2 to 4 months after introduction to the field. The vaccinated group, which remained free of anaplasmosis, showed consistently greater weight gain than did the controls. Among the Holstein calves, the maximum weight difference in favor of the vaccinated group was 50 kg/head at 5.5 months after field exposure, and among the Brown Swiss calves, the differences in weight gain in favor of vaccinated calves at the end of the 12-month period was between 11 and 30 percent. It is concluded that the vaccine provided a means for safe adaptation of high-quality young cattle to the tropics by protecting them against what appears to be the major obstacle to this practice, anaplasmosis.