Evaluation of the stability of Ostertagia ostertagi ELISA microtitre plates over time using cow milk samples

The objective of this study was to assess the stability of ELISA plates prepared with one of three blocking agents and used with one of two conjugates at various time intervals after preparation of the plates. Two of the blocking agents used were commercially available: one termed stabilgaurd (stab) and one manufactured by SVANOVA Biotek AB Inc. (svan). The third blocking agent used was bovine serum albumin (bsa). A polyclonal rabbit anti-bovine IgG (poly) and an anti-bovine IgG monoclonal (mono) conjugate were used. Eighteen composite individual cow milk samples collected late in lactation (200-400 days in milk) were used in this study. An indirect microtitre plate ELISA that used the Ostertagia ostertagi antigen was used to quantify antibodies against the parasite, present in the milk samples. Each of six blocking agent/conjugate combinations (called systems) were used to test 18 milk sub-samples at 1, 4 and 24 weeks after blocking the plates. Plates blocked with stab and svan were kept at room temperature and an additional set were incubated at 37 degrees C so as to mimic long term storage (about 1 year) and tested only once at 4 weeks. Those blocked with bsa were frozen at -20 degrees C. Concordance correlation coefficients (CCC) and reproducibility were used to assess the agreement between test results conducted on the same milk sample at the various test-times using a particular system. Generally, there was good agreement between tests conducted at different times for all systems. However, the svan-mono and bsa-poly systems had the best agreement with overall CCC values of 96% and 93%, respectively. The svan-poly system had the lowest CCC of 75%. The CCC and reproducibility ranked the systems in a similar way. The high CCC between tests done using plates kept at room temperature and ones incubated at 37 degrees C, suggested that plates would be stable up to a year after blocking. The storage of plates blocked with svan and stab agents under room temperature, makes them more convenient to use and transport relative to bsa-blocked plates that have to be frozen.     

A prospective study of vesicular stomatitis in cattle in an enzootic region of Mexico

A prospective study of vesicular stomatitis was conducted in two bovine herds in southeastern Mexico. In July 1987, an initial serological screening showed that 64% and 87% of the 654 cattle tested negatively to vesicular stomatitis New Jersey and Indiana antibodies, respectively, using the plaque-reduction serum neutralization test. Most seropositive animals were at least 24 months of age. Based on the initial serological screening, cohorts of seronegative and seropositive cattle were monitered (January–December 1988) for the prevalence of vesicular stomatitis virus (VSV) antibodies using an enzyme-linked immunosorbent assay (ELISA). The serological results, using ELISA, indicated that no VSV activity occured in the two study herds. The seronegative cohort of cattle did not yield a positive seroconversion pattern to either VSV Indiana or New Jersey. The seropositive cohort showed a variable antibody response pattern against the VSV. There were no clinical cases of vesicular stomatitis (VS) in the two herds. The data from the national surveillance program for vesicular diseases suggested that 1988 was a year of low VSV infection incidence in southeastern Mexico.     

Milk antibodies against Ostertagia ostertagi: relationships with milk IgG and production parameters in lactating dairy cattle

The present study was carried out to evaluate the relationship between milk optical density ratios (ODRs) from an indirect Ostertagia ostertagi ELISA, total milk IgG levels and milk production and then establish a correction factor to adjust ODR. Five hundred and sixty composite milk samples collected from 358 cows on four dairy herds in June and August 2002 were used in this analysis. The average ODR was 0.34. A positive correlation was found between ODR and IgG values in milk, days in milk, age and log transformed somatic cell counts (SCC). However, ODR was negatively correlated with milk production. The IgG levels and ODR values were constant from 30 to 200 days in milk. However, ODRs increased from 200 days until the end of the lactation. After controlling for age, season, herd and SCC, an increase in milk production of 13 kg/day was associated with a reduction in ODR values of 0.052. The results of the present study suggest that ODR values are not greatly influenced by production factors. ODR follow the same pattern as the IgG variation across lactation and could be adjusted in order to compare ODR values obtained from high producing cows with those obtained from low producing animals.     

The selenium status of dairy herds in Prince Edward Island

Bulk tank milk selenium (Se) concentration was compared with mean serum Se concentration in 15 herds and was found to be an accurate reflection of the herd Se status. The Se status of 109 Prince Edward Island (PEI) dairy herds was monitored for 1 year using bulk tank milk Se concentration. Fifty-nine percent of the herds surveyed were, at some point, found to be marginal or deficient in Se, putting them at risk of disease and suboptimal production. The periods of greatest risk of deficiency were fall and winter, at which time 5% and 4%, respectively, of herds sampled fell in the range considered truly deficient in Se. Herds in which Se supplementation was provided in the form of a commercial dairy concentrate were over 4 times more likely to be Se-adequate than herds not using this method, and adjusted average daily milk yield was 7.6% greater in herds determined to be Se-adequate when compared with Se-marginal herds. We conclude that many dairy producers in PEI are providing insufficient supplementary Se in the ration to meet the recommended Se intake for lactating cows.     

Efficacy of using an internal teat sealer to prevent new intramammary infections in nonlactating dairy cattle

OBJECTIVE: To determine whether insertion of an internal teat sealer (ITS) at the end of lactation would prevent development of new intramammary infections (IMIs) during the nonlactating period. DESIGN: Controlled clinical trial. ANIMALS: 939 Holstein-Friesian dairy cows from 16 herds. PROCEDURES: Results of bacteriologic culture of milk samples collected 14 days prior to the end of lactation were used to assign cows to groups (group 1 = negative results for all quarters; group 2 = positive results for > or = 1 quarter). Quarters of cows in group 1 were treated with an ITS or a single intramammary dose of cloxacillin; quarters of cows in group 2 were treated with cloxacillin in conjunction with an ITS or with cloxacillin alone. Milk samples were collected at the end of lactation and within 8 days after calving. RESULTS: Regardless of whether the outcome of interest was new IMIs caused by any pathogens, major pathogens, environmental pathogens, or streptococci other than Streptococcus agalactiae, quarters in group 2 treated with both cloxacillin and an ITS were less likely to develop a new IMI than were quarters treated with cloxacillin alone. For cows in group 1, no significant difference in risk of new IMIs was found between treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that for dairy cattle with an IMI late in the lactation period, intramammary administration of cloxacillin at the end of lactation followed by insertion of an ITS enhanced protection against development of new IMIs, compared with use of cloxacillin alone.     

Marked, biased, filter (MBF): use of digital X-radiography and mark-recapture to partition seed lots based on sampled individual seed quality attributes

We report results of preliminary evaluations of marked, biased, filter (MBF), a method for both estimating and improving the effectiveness of separating conifer seeds. MBF integrates elements of X-radiographic seed quality assessment and mark-recapture methods from wildlife population sampling. Given a sample drawn from a population, individual seeds with attributes targeted for separation are labelled with a mark which biases the subsequent removal probability of other, non-marked seeds in the lot during grading and processing, after returning the sample to the population. Bias in the marking filter, in the form of extra mass or density added to seeds, minimizes the likelihood that uncertainty due to sampling error in the prior estimate will result in empty seeds remaining in the population during processing. In two experiments, a ponderosa pine seed lot was partitioned into empty and filled fractions with an air column separator. Powder dye talc was used for marking in the first trial, with low bias (<1%) and a small sample size (n = 150) with dry (2% moisture content) and soaked (26% moisture content) seed lots. A second trial conducted with two coats of spray paint used for marking and a larger sample size (n = 400) resulted in removal of 100% of non-filled seeds in the population. A simulation was conducted to evaluate sample statistics upon which to base the value of threshold bias, τ, below which seeds in an X-rayed sample should be marked to achieve consistent separation. Estimating the marking threshold based on quantiles of filled seeds most consistently resulted in removal of the non-filled fraction. MBF is a useful method for statistically linking one or more individual seed quality attributes extracted from X-ray image analysis with population-level processing of seed lots.     

Relationships among milk urea-nitrogen, dietary parameters, and fecal nitrogen in commercial dairy herds

Our study objective was to determine the ability of milk urea-nitrogen concentrations ([MUN]) to predict fecal nitrogen concentrations ([Fecal N]) in commercial dairy herds. A total of 83 dairy herds were each visited 3 times within 48 h after a monthly herd milk test. For each farm visit, forages were sampled for nutrient analyses, which were entered into a computerized ration evaluator, and fecal samples were taken per rectum from each of 6 cows (2 early-, 2 mid-, and 2 late-lactation). Fecal samples were pooled, mixed, and analyzed for nitrogen content. Fecal nitrogen concentrations were compared with the routinely measured nutritional parameters from the ration evaluation, and the herd average [MUN] for the previous milk test date using mixed linear regression analyses. Total protein supplied in the ration was significantly positively associated with [Fecal N], but herd average [MUN] was not associated (P > 0.10) with [Fecal N].