Serum protein concentrations as predictors of serum immunoglobulin G concentration in neonatal foals

Immunity transfer in mule foals fed with good IgG quality colostrum

While the passive transfer of immunity in horse and donkey foals has been extensively studied, there is limited information for mule foals. Immunoglobulin type G (IgG) and serum total protein concentration (TP) were assessed at different sampling times to evaluate the correlation between serum radial immunodiffusion (SRID) with electrophoresis, refractometry, and dry chemistry analyzer (Biuret), and to estimate serum IgG concentrations using serum TP in mule foals. We analyzed a total of 30 samples collected at birth, and at 6, 12, 24, and 48 h of life from 6 mule foals by SRID, electrophoresis TP, biuret TP, and refractometry TP. The SRID IgG concentration significantly increased from birth until T6 (p < 0.001). Serum TP analyzed with refractometry revealed differences between T0 and T12, T24 and T48 (p < 0.05), while a significant difference was observed with the biuret method between T0 and all the other sampling times (p < 0.001). A strong correlation was found between IgG SRID and biuret TP (r = 0.69, p < 0.001), and a good correlation existed between IgG SRID, refractometry TP, and electrophoresis TP (r = 0.44, p < 0.01 and r = 0.39, p < 0.05, respectively). All methods can be used to estimate the passive transfer of immunity in mule foals. TP refractometry and biuret TP values can be used to determine serum IgG concentrations in the blood of mule foals on their first day of life through the application of a specific equation.

Changes in serum total protein and immunoglobulin G concentrations and Brix percentages in neonatal Arabian foals from birth up to 21 days of age

The aim of this study was to evaluate changes in the serum immunoglobulin G (IgG) and serum total protein (STP) concentrations and serum Brix percentages of neonatal Arabian foals during first 3 weeks of life. Blood samples were collected from 12 apparently healthy foals by jugular venipuncture at birth and at 12-hours, 24-hours, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15 and 21 days of age. Serum IgG and STP concentrations and Brix percentages were measured by the radial immunodiffusion assay, and digital STP and Brix refractometers, respectively. Based on the serum IgG concentrations measured at 24 h, two foals were diagnosed with failure of transfer of passive immunity (FTPI). While IgG concentrations were determined using the data of foals with adequate transfer of passive immunity, other calculations were made using the data of all foals. The mean IgG concentration of the foals increased from birth (<200 mg/dl) to 12 (2068.5 mg/dl) and 24 h (2184.7 mg/dl), and progressively decreased up to 21 days of age (1318.5 mg/dl). The serum IgG concentrations at 12 h were highly correlated with each of the IgG concentrations measured over the 21-day period. The serum IgG and STP concentrations and Brix percentages of the foals diagnosed with FTPI at 12 h did not reach the adequate strata over time. These results suggest that foals can be reliably tested for passive immunity status at 12 h after birth.

Evaluation of refractometry methods for estimating passive immunity status in neonatal foals

The objective of this cross-sectional study was to determine the accuracy of the digital Brix and serum total protein (TP) refractometers for estimating different passive immunity status in neonatal foals. In total, 18- to 40-h old purebred Arabian foals (n = 185) were used. Serum TP concentrations, total solid percentages and IgG concentrations were measured with a digital serum TP refractometer, digital Brix refractometer and the gold standard radial immunodiffusion (RID) assay, respectively. Correlation coefficients were calculated between the refractometer and RID assay results. A receiver operating characteristic analysis was used to select the optimal cut-offs for both refractometers. Test performance and agreement were evaluated using diagnostic test characteristics at optimal thresholds and areas under the ROC curve, and by calculating Cohen's kappa coefficient. The sensitivity and specificity of the digital Brix refractometer at optimal cut-offs (≤7.8%, ≤7.9%, ≤8.2%, ≤8.3%, ≤9.0%) were 100 and 69.3%; 100% and 68.5%; 70.5% and 71.0%; 88.3% and 85.5%; 88.1% and 76% to estimate RID-IgG of <400 mg/dL, <800 mg/dL, <1500 mg/dL, <2500 mg/dL and < 3000 mg/dL, respectively. The sensitivity and specificity of the digital serum TP refractometer at optimal cut-off (≤4.6 g/dL, ≤4.6 g/dL, ≤4.8 g/dL, ≤5.0 g/dL, ≤5.4 g/dL) were 100 and 69.3%; 100% and 72.8%; 90% and 72.8%; 72.9% and 83.9%; 84.4% and 88% to estimate RID-IgG of <400 mg/dL, <800 mg/dL, <1500 mg/dL, <2500 mg/dL and < 3000 mg/dL, respectively. In conclusion, the refractometers showed a good potential as screening tools for the estimation of different IgG concentrations in neonatal foals.

Evaluation of Optical Refractometer for Assessing Failure of Transfer of Passive Immunity in Foals

The aim of the present study is to evaluate the correlation between the total protein measured by an optical refractometer and the concentration of IgG by radial immunodiffusion (RID) to determine the performance of the optical refractometer to diagnose the failure of passive transfer of immunity (FPTI) in 12-hour-old foals. Blood was collected from foals (n = 30) 12 hours after birth. A study was carried out to measure the serum IgG concentration by RID test and measure total protein (TP) by optical refractometer. The correlation coefficient was measured between the TP concentration and the IgG-RID. Correlation was made between the IgG-IDR levels of colostrum in mares and the IgG-IDR concentration of the plasma of the foals. A ROC curve was made to identify the ideal cutoff point, in addition to the tests for sensitivity and specificity. The area under the curve (AUC) was calculated. The IgG concentration by RID was positively correlated with a refractometer. Colostrum IgG concentration by RID was moderately correlated with foal plasma IgG-RID concentration. In the ROC curve, AUC was 0.931, and the cutoff point found was ≤5,7 g/dL as the most optimal combination, with 100% sensitivity and 73.3% specificity. Thus, it can be concluded that the total protein concentration by refractometer shows effective utility in the evaluation of FPTI in foals since they are highly sensitive, associated with a low cost, easy to handle, and easily carried out in the field.

Evaluation of Different Methods to Estimate the Transfer of Immunity in Donkey Foals Fed with Colostrum of Good IgG Quality: A Preliminary Study

Simple Summary

Little is known about the passive transfer of immunity in donkey foals and about the different types of analysis that can be performed to assess it. The aims of the present study were to evaluate the correlation between IgG Serum Radial Immunodiffusion, Electrophoresis Gamma Globulins, Electrophoresis Total Protein and the Serum Total Protein analyzed by Refractometry and by Dry Chemistry Analyzer (Biuret) and to estimate serum IgG concentrations using Serum TP. IgG Serum Radial Immunodiffusion showed a good correlation with Electrophoresis Gamma Globulins and a high correlation with Total Protein Electrophoresis, Biuret and Refractometry. All the tests performed may be a useful to estimate the serum IgG in donkey foals’ blood in the first day of life using a specific equation.

Abstract

The aims of the present study were to evaluate the correlation between IgG Serum Radial Immunodiffusion (SRID), Electrophoresis Gamma Globulins (EGG), Electrophoresis Total Protein (ETP) and the serum total protein (TP) analyzed by refractometry and by a dry chemistry analyzer (Biuret) and to estimate serum IgG concentrations using serum TP. A total of 36 samples collected at four different times (birth, 6, 12, 24 h after birth) from nine Amiata donkey foals were evaluated with SRID, EGG, ETP, serum TP Biuret and refractometry. SRID IgG concentration increased significantly over time until T12. Serum TP analyzed with refractometry, electrophoresis and Biuret showed a statistically significant difference between T0 and T6 vs. T12 and T24. A good or strong correlation was found between different tests performed. Equations to quantify serum IgG were created and can be used for estimating the donkey foals’ serum IgG in the first day of life. Serum TP refractometry showed a high correlation with SRID IgG (0.91) which may be a particularly useful and economic instrument to estimate the transfer of immunity in donkey foals during the first day of life. Further studies evaluating a high number of animals are needed in order to set specific cut-off values.

Usefulness of digital and optical refractometers for the diagnosis of failure of transfer of passive immunity in neonatal foals

BACKGROUND

Neonatal foals with failure of transfer of passive immunity (FTPI) are at higher risk of morbidity and mortality. Successful treatment of FTPI is time-dependent, thus rapid and accurate measurement of serum IgG concentration is important for the management and care of neonatal foals.

OBJECTIVES

To validate the use of digital and optical refractometers for assessing FTPI in neonatal foals and compare the diagnostic performance and level of agreement of the two refractometers to the reference standard radial immunodiffusion (RID) assay.

STUDY DESIGN

A retrospective validation study.

METHODS

Serum samples (n = 253) were collected from 230 foals admitted to the Veterinary Teaching Hospital and Ambulatory Equine Service between 2012 and 2017. The serum IgG concentrations were measured by the reference RID assay, digital Brix and optical refractometers. The correlation between results of two refractometers and RID assay was assessed. A receiver operating characteristic curve was created and used to identify the optimal cut-offs for evaluating sensitivity and specificity of the two refractometers to detect foals with complete and partial FTPI.

RESULTS

The RID-IgG concentrations were positively correlated with the Brix scores obtained from a digital refractometer (r = 0.73, P = 0.001) and serum total protein obtained from an optical refractometer (r = 0.72, P = 0.001). The sensitivity and specificity of the digital Brix refractometer at optimal cut-off (≤7.8% Brix) were 88.1 (95% CI: 74.4-96.0) and 67.7% (95% CI: 60.6-74.3) to detect RID-IgG<4 g/L and 79.0 (95% CI: 68.5-87.3) and 77.3% (95% CI: 69.8-83.8) to detect RID-IgG≤8 g/L, respectively. The sensitivity and specificity of the optical refractometer at optimal cut-off (≤42 g/L) were 86.1 (95% CI: 72.1-94.7) and 70.9% (95% CI: 63.9-77.3) to detect RID-IgG<4 g/L and at cut-off (≤44 g/L) were 82.9 (95% CI: 73.0-90.3) and 72.7% (95% CI: 64.8-79.6) to detect RID-IgG≤8 g/L, respectively.

MAIN LIMITATIONS

The number of diseased foals was small to investigate the validity of the selected cut-off values for assessing FTPI in sick foals.

CONCLUSIONS

The two refractometers exhibit utility as rapid, inexpensive screening tests and have a good sensitivity for assessing FTPI in neonatal foals.

Validation of a Point-of-Care Quantitative Equine IgG Turbidimetric Immunoassay and Comparison of IgG Concentrations Measured with Radial Immunodiffusion and a Point-of-Care IgG ELISA

BACKGROUND

Point-of-care (POC) diagnostic tests with good sensitivity and specificity are needed for diagnosing failure of transfer of passive immunity (FTPI) in foals. Turbidimetric immunoassays (TIA) have these characteristics and provide quantitative results. A commercially available TIA-based POC test (POC-TIA) has not been validated in horses.

OBJECTIVE

To validate a POC-TIA and compare results of POC-TIA, a POC-ELISA, and radial immunodiffusion (RID).

ANIMALS

Heparinized blood samples (n = 127) from 48 hospitalized foals (<12 hour to 48 days).

METHODS

Prospective validation study. IgG concentrations were measured using RID (gold standard), POC-TIA, and POC-ELISA. Agreement between assays was assessed using Bland-Altman analysis. Sensitivity and specificity were calculated using ROC curves. Inter- and intra-assay coefficients of variation (CVs) and linearity were evaluated for POC-TIA.

RESULTS

The mean bias (95% limits of agreement) between RID and POC-TIA was -4 (-185 to 176), 27 (-201 to 255), and 308 (-377 to 993) mg/dL for samples with IgG concentrations of <400, 400-800, and >800 mg/dL, respectively. Sensitivity and specificity at optimal cutoff were 94 and 100% for the POC-TIA and 94 and 100% for the POC-ELISA to detect IgG <400 mg/dL, and 85 and 87% (POC-TIA) and 69 and 79% (POC-ELISA) to detect IgG ≤800 mg/dL. Intra- and interassay CVs for POC-TIA ranged between 1.6-3.8 and 11.9-18.8%, respectively. Linearity of the dilution series was preserved (R² > 0.96).

CONCLUSIONS AND CLINICAL IMPORTANCE

The POC-TIA provided unambiguous results and had sufficient sensitivity, specificity, accuracy, and precision to be used as an alternative to other POC tests to assess FTPI in foals.

Validation of IgG cut-off values and their association with survival in neonatal foals

REASONS FOR PERFORMING STUDY

Serum immunoglobulin (IgG) assessment in neonatal foals is considered standard care in equine hospitals to determine immunity and overall health. However, cut-off values of IgG to predict complete or partial failure of transfer of passive immunity (FTPI) were developed 30 years ago and are largely empirical with little prospective or statistical data to support their use or association with outcome.

OBJECTIVES

To critically evaluate the traditional cut-off values of IgG in the assessment of FTPI (IgG < 8 g/l), determine the association between various degrees of FTPI and likelihood of nonsurvival and examine whether FTPI can be predicted by serum total protein (TP), albumin and globulin in hospitalised foals.

STUDY DESIGN

Multicentre, cross-sectional study.

METHODS

We evaluated clinicopathological variables in 597 foals ≤ 7 days old from 3 equine hospitals including serum IgG, fibrinogen, TP and albumin concentrations. Foals were divided into 3 groups by diagnosis: healthy, sick nonseptic and septic. The aforementioned variables in addition to globulin concentrations were evaluated in a subset of 118 foals. Univariate, multivariate and multinomial logistic regression were used to compute odds ratios for nonsurvival in these foals.

RESULTS

Our findings support use of the traditional cut-off value of > 8 g/l as adequate transfer of passive immunity (ATPI). Odds of nonsurvival increased in proportion to lower IgG concentrations. Higher TP concentrations were associated with lower likelihood of FTPI; however, higher albumin concentrations were associated with a greater likelihood of FTPI. A regression equation was created to predict IgG in foals using serum proteins.

CONCLUSIONS

Serum IgG values of <8 g/l in hospitalised foals were proportionally associated with mortality. We recommend immediate assessment of IgG concentrations in hospitalised foals and those with FTPI should receive prompt immunotherapy. The summary is available in Chinese - see Supporting information.

Serum total proteins and related electrophoretic fractions in growing foals

Abstract. The aim of this study was to evaluate the changes of serum total proteins, albumin, α1-, α2-, β1-, β2 and γ-globulins in growing foals during the first month of life. Nine clinically healthy foals (five females and four males, mean body weight 39.00 ± 3.50 kg) were enrolled in the study. From each animal, blood samples were collected by jugular venipuncture every 3 days during the first month of life starting from the day of birth. Serum concentration of total proteins, albumin, α1, α2, β1, β2 and γ-globulins was assessed. One-way repeated measures analysis of variance (ANOVA), followed by Bonferroni post hoc comparison test, was used to determine statistically significant effect of the day of life on studied parameters. A statistically significant effect of the day of life on serum total proteins (P < 0.0001), albumin (P < 0.0001) and γ-globulins (P < 0.005) was observed during the first month of life. Our findings emphasize the importance of establishing different reference intervals for serum electrophoretic protein profiles in growing foals based on their physiological status. This study provides useful information that could help clinicians to better interpret clinical data and diagnose equine neonatal disease.