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.
Objective—To evaluate the use of a polymerase
chain reaction (PCR) assay in detecting bovine leukosis
virus (BLV) in adult dairy cows.
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
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
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)
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.
Objective—To determine whether strength of serologic
recognition of bovine leukosis virus (BLV) by use
of ELISA is associated with blood lymphocyte counts.
Animals—161 cows with positive results of ELISA
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)
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
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.
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.
Objective—To determine sensitivity and specificity of
a cow-side immunoassay kit for assessing IgG concentration
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)
Objective—To evaluate several practice-adapted
assays for determination of passive transfer status in
Animals—24 llama and 9 alpaca crias.
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
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
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 ) or short days (8 h of light/d ) 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.