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  • Author or Editor: Dusty W. Nagy x
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Abstract

Objective—To determine the interval to provirus and serum antibody detection (via PCR assay and ELISA, respectively) in calves after experimental inoculation with bovine leukemia virus (BLV).

Animals—8 colostrum-deprived, BLV-negative Holstein bull calves (≥ 6 weeks old).

Procedures—Via IM injection, each calf received a fresh whole-blood inoculum (day 0) calculated to contain 2 × 106 lymphocytes. Blood samples for the ELISA and PCR assay were collected from calves immediately prior to inoculation and weekly thereafter for 7 weeks. Mean and median number of weeks to PCR-detected conversion of BLV status and seroconversion were calculated. Point sensitivity and cumulative sensitivity of the 2 assays were calculated at each sample collection. At each sampling time, the proportion of calves identified as infected by the cumulative weekly ELISA and PCR assay results was compared by use of a Fisher exact test.

Results—In 5 calves, conversion of BLV status was detected via PCR assay before seroconversion was identified. However, seroconversion preceded PCR-detected conversion in 2 calves. In 1 calf, both assays yielded positive results at the same test date. These differences were not significant.

Conclusions and Clinical Relevance—In experimentally inoculated BLV-negative calves, conversion of BLV status was detected via PCR assay more quickly than via ELISA; this difference was not significant and probably not clinically important. The PCR assay may be useful as a confirmatory test in animals of exceptional value; tests based on viral identification may become critically important if vaccines against BLV infection are developed and marketed.

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in American Journal of Veterinary Research

Abstract

Objective—To evaluate the use of a polymerase chain reaction (PCR) assay in detecting bovine leukosis virus (BLV) in adult dairy cows.

Design—Prospective study.

Animals—223 adult dairy cows.

Procedure—Cows were tested for BLV status by use of an ELISA and a PCR assay. Sensitivity, specificity, predictive values of positive and negative tests, and the percentage of cows correctly classified by PCR assay were calculated. Ninety-five percent confidence intervals were calculated for sensitivity and specificity.

Results—Sensitivity and specificity were 0.672 and 1.00, respectively. Prevalence of BLV in this herd was 0.807. Predictive value of a positive test was 1.00, and predictive value of a negative test was 0.421. The percentage of cows correctly classified by PCR assay was 73.5%.

Conclusions and Clinical Relevance—A positive PCR assay result provided definitive evidence that a cow was infected with BLV. Sensitivity and negative predictive value for PCR assay were low. Consequently, PCR assay alone is unreliable for routine detection of BLV in herds with high prevalence of the disease. (J Am Vet Med Assoc 2003;222:983–985)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine the prevalence of detectable serum IgG concentrations in calves prior to ingestion of colostrum and to assess whether a detectable IgG concentration was related to dam parity, calf birth weight, calf sex, season of calving, or infectious agents that can be transmitted transplacentally.

Animals—170 Holstein dairy calves.

Procedures—Serum samples were obtained from calves prior to ingestion of colostrum, and serologic testing for bovine viral diarrhea virus (BVDV) and Neospora caninum was performed. Relative risk, attributable risk, population attributable risk, and population attributable fraction for calves with a detectable serum IgG concentration attributable to positive results for N caninum and BVDV serologic testing were calculated. Logistic regression analysis was used to determine whether dam parity, calf sex, season of calving, and calf weight were associated with precolostral IgG concentration.

Results—90 (52.9%) calves had a detectable total serum IgG concentration (IgG ≥ 16 mg/dL). Relative risk, attributable risk, population attributable risk, and population attributable fraction for calves with a detectable serum IgG concentration attributable to positive results for N caninum serologic testing were 1.66, 0.34, 0.014, and 0.03, respectively. Calf sex, calf birth weight, and season of calving were not significant predictors for detection of serum IgG in precolostral samples.

Conclusions and Clinical Relevance—Prevalence of IgG concentrations in precolostral serum samples was higher than reported elsewhere. There was no apparent link between serum antibodies against common infectious agents that can be transmitted transplacentally and detection of measurable serum IgG concentrations.

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in American Journal of Veterinary Research

Abstract

Objective—To determine whether strength of serologic recognition of bovine leukosis virus (BLV) by use of ELISA is associated with blood lymphocyte counts.

Design—Prospective study.

Animals—161 cows with positive results of ELISA for BLV.

Procedure—Sample-to-positive ratio (S:P), which is the ratio between the test sample and a positive control sample, was compared among lymphocytotic and nonlymphocytotic cows. A regression model was constructed to evaluate the association between blood lymphocyte concentration and S:P, age, and the interaction of these terms.

Results—Mean S:P differed significantly between lymphocytotic (2.58 ± 0.36) and nonlymphocytotic (2.38 ± 0.39) cows. Age and S:P were significantly associated with lymphocyte count.

Conclusions and Clinical Relevance—Sample-topositive ratio and lymphocyte count were related; however, cows with high S:P were not always lymphocytotic. Culling cows on the basis of S:P will reduce the herd load of infectious virus faster than random culling of ELISA-positive cows; however, culling on the basis of lymphocyte count will eliminate a greater proportion of the reservoir of infection. (J Am Vet Med Assoc 2002;220:1681–1684)

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in Journal of the American Veterinary Medical Association
History

A 2-day-old 44-kg (97-lb) purebred female Holstein calf was evaluated for weakness, signs of depression, and inability to stand unsupported. Immediately after birth, the calf could stand and was tube fed with approximately 4 L of colostrum. Twenty-four hours after birth, the calf was standing and suckled its daily requirement of milk replacer, but 48 hours after birth, the calf was recumbent and only drank half of its 2-L morning milk replacer feeding. The owner had treated the calf with 100 mg of tulathromycin that morning. On initial examination, rectal temperature (39°C [101.5°F]) and heart rate (120 beats/min) were

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine the effect of time interval from birth to first colostrum feeding on colostrum intake and serum IgG concentration and the effect of varying colostral volume intake and colostral IgG concentration on the probability of failure of passive transfer (FPT) in bottle-fed calves.

Design—Randomized controlled study.

Animals—104 calves.

Procedures—Equal numbers of calves were randomly assigned to groups and fed 3 L of their dam's colostrum at 1, 2, 3, or 4 hours after birth by use of a nipple bottle. Calves were allowed to feed for 15 minutes, and intake was recorded. A second 3-L bottle feeding of colostrum was offered at 12 hours of age.

Results—17.2% of calves ingested 3 L of colostrum at the first feeding and 3 L at 12 hours of age. Calf age, up to 4 hours, had no significant effect on the calf's ability to ingest colostrum or on 48-hour serum IgG concentration. Colostral intake at 1, 2, 3, or 4 hours had no effect on intake at the second feeding. Probability of FPT in calves ingesting 3 L at both feedings was < 0.05.

Conclusions and Clinical Relevance—Allowing calves fed by nipple bottle to ingest as much colostrum as they can within 4 hours after birth and at 12 hours of age substantially reduced the probability of FPT. Bottle-fed calves that do not ingest 3 L of colostrum within the first 4 hours after birth should be targeted for oroesophageal intubation.

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine sensitivity and specificity of a cow-side immunoassay kit for assessing IgG concentration in colostrum.

Design—Prospective study.

Animals—76 dairy and 11 beef cows of various parities.

Procedure—Colostrum from first, second, and third milkings and milk samples were collected, and IgG concentration was determined by means of radial immunodiffusion. The immunoassay was performed according to the manufacturer’s instructions, and sensitivity and specificity were calculated by comparing results of the immunoassay (positive vs negative) with results of immunodiffusion (< 50 g/L vs ≥ 50 g/L).

Results—135 colostrum or milk samples were collected. Mean ± SD colostral IgG concentrations, determined by means of radial immunodiffusion for dairy and beef cows were 65.4 ± 51.4 g/L and 114.8 ± 42.7 g/L, respectively. Mean IgG concentrations for first-, second-, and third-milking colostrum samples and for milk samples were 92 ± 49.0 g/L, 74.6 ± 45.1 g/L, 47.5 ± 32 g/L, and 6.8 ± 3.8 g/L, respectively. Sensitivity of the immunoassay (ie, percentage of samples with IgG concentration < 50 g/L with a positive immunoassay result) was 93%, and specificity (ie, percentage of samples with IgG concentration ± 50 g/L with a negative immunoassay result) was 76%.

Conclusions and Clinical Relevance—Results suggested that the immunoassay kit was an acceptable cow-side test to identify colostrum samples with IgG concentrations < 50 g/L. The immunoassay kit should be useful in screening colostrum for adequate IgG concentration before feeding to calves or storage. (J Am Vet Med Assoc 2005;227:129–131)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To evaluate several practice-adapted assays for determination of passive transfer status in crias.

Animals—24 llama and 9 alpaca crias.

Design—Prospective study.

Procedure—Serum IgG concentration was measured by use of a radial immunodiffusion assay when crias were 45 to 51 hours old. Results were compared with serum γ-glutamyltransferase (GGT) activity, serum total protein, albumin, globulin, and total solids concentrations, and results of commercially available and traditional sodium sulfite turbidity (SST) tests.

Results—Mean (± SD) serum IgG concentration was 1,762 ± 1,153 mg/dl. On the basis of a threshold value of 1,000 mg of IgG/dl at 48 hours of age, 5 of 33 (15.15%) crias had failure of passive transfer. Serum total solids, protein, and globulin concentrations were significantly associated with serum IgG concentration, whereas serum GGT activity and serum albumin concentration were not. Serum IgG concentrations were significantly different among crias with negative, 2+, and 3+ scores on the traditional SST test. Serum IgG concentrations were not significantly different between crias with negative and 100 mg/dl scores or 100 and 300 mg/dl scores on the commercially available SST test. However, all other comparisons between crias with different scores revealed significant differences. Sensitivity and specificity ranged between 0 and 1, depending on the test and endpoint selected.

Conclusion and Clinical Relevance—The commercially available SST test and determination of serum total protein and globulin concentrations are suitable methods for assessing passive transfer status in llama and alpaca crias. (J Am Vet Med Assoc 2000;216:559–563)

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in Journal of the American Veterinary Medical Association

Abstract

Objective—To identify cow and management factors associated with colostral IgG concentration in dairy cows.

Design—Prospective observational study.

Animals—81 multiparous Holstein-Friesian cows from a single herd.

Procedures—Serum was obtained at the start of the nonlactating period, and cows were assigned to 1 of 4 photoperiod groups: natural day length (n = 22 cows), long days (16 h of light/d [21]) or short days (8 h of light/d [20]) for the entire nonlactating period, or natural day length followed by short days for the last 21 days of the nonlactating period (18). Serum and colostrum were collected at the first milking after calving. Regression analysis was used to investigate associations between colostral IgG concentration and the interval between calving and first milking, colostral volume, photoperiod, length of the nonlactating period, and season of calving.

Results—Colostral IgG concentration decreased by 3.7% during each subsequent hour after calving because of postparturient secretion by the mammary glands. The interval between calving and first milking and the colostral volume were significantly and negatively associated with colostral IgG concentration, with the former effect predominating. Photoperiod had no effect on colostral IgG concentration or volume. Serum protein concentration at calving correlated poorly with colostral IgG concentration.

Conclusions and Clinical Relevance—Dairy producers should harvest colostrum as soon as possible after calving to optimize transfer of passive immunity in neonatal calves. Photoperiod can be manipulated without adversely affecting colostral IgG concentration.

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in Journal of the American Veterinary Medical Association