Determination of colostrum quality using Brix refractometer in sheep.

In this study, we aimed to determine the quality of colostrum in sheep by using Brix refractometer. The research included 100 sheep of Merino X Kivircik crossbred. From each, we collected 15 mL of colostrum samples in falcon tubes within the first 8 h after delivery. Mean colostral IgG level of sheep was 156.68 ± 7.23 g L-1, optical and digital Brix refractometer values (%) were determined as 27.43 ± 0.53 and 27.69 ± 0.60, respectively. Ewes carrying twin lambs produced significantly higher quality colostrum than those carrying single lambs. However, parity did not affect the colostrum quality. Optical and digital Brix values were correlated with gold standard radial immunodiffusion (RID) colostral IgG level (r = 0.70 and r = 0.64, respectively). Also, optical and digital Brix refractometers were found to be highly correlated (r = 0.98, P < 0.001). While the optimal Brix value was 22% for the 50, 60 and 70 g L-1 IgG threshold values (by means of RID as the potential good quality threshold value for ewe colostrum quality), this value was 23% for 80 g L-1. We can conclude that Brix refractometers is a valuable tool for determining ewe colostrum quality. A cut point of 22% Brix for defining good quality colostrum in ewes was most appropriate for our data.

Assessing colostral and serum immunoglobulin G in alpacas using Brix refractometry and total serum protein.

The adequate transfer of passive immunity is a critical factor in neonatal development and survivability. Although well documented in the dairy and equine industries, the recognition of inadequate immunoglobulin transfer on-farm and its impact on the ability of alpaca cria to thrive is largely unknown. Colostrum samples were collected from female alpaca within 24 h of parturition by the owners and whole blood collected from cria by the investigators between 1 and 7 days of age. Direct IgG concentration of milk and serum was determined using radial immunodiffusion assay (RID) and was indirectly estimated using optical and digital Brix refractometry for total solids and clinical refractometry for total serum protein. There was a strong correlation between optical and digital Brix refractometry, and colostral IgG concentration determined by RID. There was a moderate correlation between serum IgG concentration determined by RID and total serum protein in crias. Optical and digital Brix refractometry for colostral IgG estimation and total serum protein for serum IgG estimation are reliable, accurate and easy-to-use tools that can be used on-farm by trained, competent technicians to assess a failure of passive transfer in alpacas. A pilot study at one property only was performed, due to COVID-19 travel restriction interference. Further research is required to determine the reference intervals for these tools to be practical.

Characterization of lyophilized equine colostrum.

Foals require maternal colostrum in the first hours of life to prevent failure of transfer of passive immunity (FTIP). Innovative storage methods such as lyophilization may enable conservation of colostrum immunoglobulins by a differentiated process of dehydration. The current study aimed to compare the quality of equine colostrum after freezing and after the lyophilization process. Thirty-one pregnant Quarter Horse mares were used. The IgG concentration of frozen and lyophilized colostrum was determined by simple radial immunodiffusion (SRID) and Brix refractometry. The physical-chemical composition (pH, total protein (TP), fat, lactose, salts, total solids (TS), and density) of the samples was evaluated and the lyophilized colostrum reconstitution test was performed. There were no significant differences (P > 0.05) in the variables IgG, fat, lactose, salts, TS, density, and pH between samples measured before and after lyophilization. There was a significant difference (P < 0.05) between the Brix average and the TP of the frozen and lyophilized colostrum samples. Lyophilization resulted in a small reduction (6.55%) in the IgG concentration measured by SRID. A strong positive correlation was observed between colostrum density and IgG concentration by SRID (r = 0.76) and between Brix and IgG concentration by SRID (r = 0.77). In the reconstitution test, the lyophilized colostrum was easily rehydrated in water, with full dilution, and remained stable. Lyophilization could be an alternative for the conservation of mare colostrum, since it is a very efficient process for retaining the physicochemical characteristics of the product, with minimal loss, particularly of IgG.

Estimating IgG concentration directly by radial immunodiffusion or indirectly by refractometry measure of serum total protein lack precision.

OBJECTIVE: To establish and compare the precision of serum total protein (STP) measured by an optical refractometer to the precision of IgG concentrations measured using radial immunodiffusion (RID), the reference test for quantifying IgG in neonatal calves. SAMPLE: 6 sera with previously measured IgG concentration using RID from neonatal beef calves were selected from 3 stratum: low-serum IgG stratum between >5.0 and <15.0g/L(n = 4); moderate-serum IgG stratum between 35.0-45.0g/L(n = 1); high-serum IgG stratum between 60.0-70.0g/L(n = 1). METHODS: STP was measured 13 times with an optical refractometer. IgG concentrations were measured 28 times with a commercial bovine IgG RID for each sera. The homogeneity of variance within the tests was evaluated with the Levene test (α = 0.10). Unrestricted random sampling bootstrapping (5,000 repetitions) was used to calculate the coefficient of variation (CV) for each serum and test. The homogeneity of variance between simulated test CVs by serum was evaluated (α = 0.10). Differences between simulated test CV by serum were assessed with the Kruskal-Wallis test (α = 0.05). RESULTS: No difference was observed in the variance for STP between sera (P = .39). The average CV for STP was 4.2%, 10.1% for the low IgG stratum, and 15.5% for the moderate/high IgG stratum. Variance differed in serum IgG concentration (P < .0001). Serum with higher IgG concentrations had more variance. Simulated CV for STP and IgG had homogeneity of variance for only 1 sera (P = .31). STP had a smaller CV compared to IgG for every serum (P < .0001). CLINICAL RELEVANCE: Estimating IgG concentration directly by RID or indirectly by STP lacks the precision that might affect diagnostic interpretation regarding a calf's absorption of maternal antibodies.

Evaluation of an immunochromatographic point-of-care test for the detection of failure of transfer of passive immunity in calves.

BACKGROUND: As calves are born without circulating immunoglobulin G (IgG) they depend on transfer of passive immunity via colostrum within the first hours of life. If calves are not sufficiently supplied with high qualitative colostrum they suffer from Failure of Transfer of Passive Immunity (FTPI). The objectives of this study were to evaluate a calf-side point-of-care test to detect calves with FTPI and to evaluate the cut-offs for a positive test result. Two hundred fifty calves from 11 dairy farms (born between September 2021 and September 2022) were included, whereof 23 were excluded due to incomplete data. Twelve to 16 h post partum the farmers carried out a point-of-care test (FASTest® IgG bovine, Megacor, Austria) using a whole blood sample. Between the 3rd and the 6th day of age, all calves were physically examined and blood samples were collected to carry out further point-of-care tests using whole blood supernatant and plasma and for measuring the Brix values in serum and plasma. Brix values in serum were used as reference for the evaluation of the point-of-care test between the 3rd and the 6th day of age, as radial immunodiffusion assays could not be conducted simultaneously. RESULTS: Brix values were not normally distributed (median at 8.6% and 9.3% in serum and plasma). In this study, the cut-off values for the point-of-care tests using whole blood supernatant and plasma were at 8.3% Brix in serum. FASTest® IgG bovine shows high sensitivities of 90% and 84% and specificities of 70% and 72% for whole blood supernatant and plasma. CONCLUSIONS: Of the 227 investigated calves, 39.7% showed Brix values of < 8.4% (cut-off for FTPI) which indicates an urgent need to improve colostrum management. The results of the study suggest that the FASTest® IgG bovine is a suitable on-farm method to assess FTPI in whole blood supernatant and plasma of calves between the 3rd and the 6th day of age. However, the results also show that FASTest® IgG bovine is not adequate to test for FTPI using whole blood at 12 to 16 h post partum.

Comparison of turbidometric immunoassay, refractometry, and gamma-glutamyl transferase to radial immunodiffusion for assessment of transfer of passive immunity in high-risk beef calves.

BACKGROUND: Attainment of adequate transfer of passive immunity (TPI) is critical to health of calves; however, studies comparing available tools for measurement of TPI in individual beef animals are limited. OBJECTIVES: To report agreement between 4 tests evaluating individual TPI status in beef calves. ANIMALS: One hundred ninety-six beef calves born to cows and heifers presenting for calving management or dystocia. METHODS: Retrospective study to assess serum immunoglobulin (IgG) concentrations via turbidimetric immunoassay (TI), gamma-glutamyl transferase (GGT), serum total protein (TP), and single radial immunodiffusion (RID; reference standard). Test agreement was evaluated using Passing-Bablok regression, Bland-Altman analysis, Cohen's kappa, and receiver operating characteristic (ROC) curves with and without covariate adjustment to determine optimal thresholds. RESULTS: Correlation between RID and test results varied: TI, ρ = 0.757; TP, ρ = 0.715; GGT: ρ = 0.413. For the TI compared to RID, regression analysis identified a constant (intercept = -0.51 [CI: -2.63, 3.05]) and proportional (slope = 1.87 [CI: 1.69, 2.08]) bias. Based on ROC, TI concentrations of ≤9.89 and ≤13.76 g/L, and TP concentrations of ≤5.5 and ≤6.0 g/dL, indicated IgG concentrations <18.0 and <25.0 g/L, respectively. CONCLUSIONS AND CLINICAL IMPORTANCE: Within this cohort of calves, TI demonstrated the best correlation with RID; however, significant bias was identified which led to frequent underestimation of IgG concentration. Serum total protein demonstrated less correlation with RID but had less misclassification than TI. Both TI and TP demonstrated less correlation for calves that received colostrum replacement prompting clinical awareness of colostrum type when evaluating individual TPI in beef calves.

Comparison of turbidometric immunoassay and brix refractometry to radial immunodiffusion for assessment of colostral immunoglobulin concentration in beef cattle.

BACKGROUND: Colostral immunoglobulin G (IgG) concentration is critical to the attainment of adequate transfer of passive immunity in cattle, however, studies comparing available tools for measurement of colostral IgG concentration in beef cattle are limited. OBJECTIVES: To report the agreement between 3 commercially available tests for evaluating IgG concentration in beef colostrum. ANIMALS: Two hundred six beef-breed cows hospitalized for calving management or dystocia. METHODS: Retrospective study to assess IgG of whole colostrum measured stall-side via turbidimetric immunoassay (TI) and brix refractometry (BRIX), compared to fat separated (FS) analysis via single radial-immunodiffusion (RID; reference standard), TI-FS and BRIX-FS. Test performance was assessed using Passing Bablock regression, Bland-Altman analysis, and area under the curve to determine optimal thresholds. RESULTS: Correlation between RID and TI-FS, BRIX-FS, or BRIX was similar (Spearman's ρ = 0.717, 0.715, 0.716, respectively) but correlation for TI was poor (ρ = 0.586). Regression analysis identified a substantial constant (-214.75 [CI: -272.03 to -178.07]) and proportional (13.24 [CI: 11.81-15.37]) bias between the RID and TI-FS which was similar for TI. TI-FS concentrations of 28.47, 38.75, and 50.62 g/L, BRIX-FS of ≤21.9%, ≤24.0%, and ≤27.4%, and BRIX of ≤21.3%, ≤23.8%, and ≤26.4% indicated IgG concentrations <50, <100, and <150 g/L, respectively; appropriate cutoffs for TI could not be generated. CONCLUSIONS AND CLINICAL IMPORTANCE: Both TI and TI-FS demonstrated a large constant and proportional bias compared to RID; BRIX and BRIX-FS were well correlated with RID and remain a reliable method for estimation of colostral IgG concentration in beef cattle.

Defining optimal thresholds for digital Brix refractometry to determine IgG concentration in ewe colostrum and lamb serum in Scottish lowland sheep flocks.

This research aimed to define thresholds for ewe colostrum and lamb serum Brix refractometer measurements in lowland Scottish sheep. This would facilitate the use of this convenient, sheep-side test, enabling quick and accurate identification of poor quality colostrum and prevention of failure of transfer of passive immunity (FTPI) in lambs. Secondary aims were to identify risk factors for poor colostrum quality and FTPI in lambs. Serum samples (n = 233) were collected from lambs between 24 and 48hrs after birth, from four lowland Scottish meat sheep farms. Pre-suckle colostrum samples (n = 112) were also collected from ewes on two of these farms. Farmers provided information on litter size, ewe body condition score, ewe breed and dystocia. Duplicate digital Brix refractometer measurements were compared with immunoglobulin G (IgG) radial immunodiffusion (RID) testing for all colostrum and serum samples. Receiver operating characteristic (ROC) curves were used to redefine thresholds for Brix testing in colostrum and serum. Linear regression models were constructed with colostrum and serum IgG concentration as the outcomes of interest. Colostrum and serum IgG concentrations were highly variable. The prevalence of inadequate colostrum quality (using <50 g/L IgG on RID) was 4.5% (95% CI = 1.5 - 10.1) and the prevalence of FTPI (using <15 g/L IgG in serum on RID) was 7.73% (95% CI = 4.64-11.93). A ewe's colostrum IgG concentration was significantly and positively associated with the serum IgG concentration of her lamb(s) (p = 0.02). ROC analysis defined a Brix threshold for adequate colostrum quality of > 22.10% (sensitivity 80% (95%CI=28.4-99.5), specificity 90% (95%CI=82.3-94.8)). ROC analysis defined a Brix threshold for serum of > 8.65% for adequate passive transfer of immunity in Scottish lambs (sensitivity 94% (95%CI=72.7-99.8), specificity 82% (95%CI=76.6-87.2)). To optimise passive transfer of immunity in lambs, we suggest that ewe colostrum Brix measurements be defined as 'poor' (<22%); 'fair' (22-26%) and 'good' (>26%); and lamb serum as 'poor' (<8%); 'fair' (8-9%) and 'good' (>9%). It is recommended that these tests are used as for flock screening, using samples from multiple animals.

Assessing failure of transfer of passive immunity by gamma-glutamyl-transferase activity and serum refractometry in holstein-friesian calves affected by neonatal diarrhea.

Hardly published data are available to diagnose the failure of transfer of passive immunity (FTPI) in calves affected by neonatal calf diarrhea (NCD). This study evaluated the diagnostic performance and differences among optical serum total protein (STP) concentration and gamma-glutamyl-transferase (GGT) activity for assessing FTPI in diarrheic Holstein Friesian calves. 72 diarrheic and 19 healthy Holstein Friesian calves aged 1 to 10 days were enrolled. Each calf underwent a complete clinical examination and dehydration assessment. The effect of dehydration status and age on the correlation between the two methods under study (STP and GGT) and the gold standard (Immunoglobulin G [IgG] measured with RID) was investigated with Spearman's correlation index R for ranks. Serum total protein concentration and GGT activity were analyzed by receiver operating characteristic (ROC) curve analysis to identify the optimal cut-off point to distinguish between diarrheic calves with or without FTPI, also considering the effects of dehydration and age. The results show that GGT activity was affected by the age of calves, while STP was influenced by dehydration. The cut-offs to distinguish calves with IgG < 10 g/L were < 52 g/L of STP in normohydrated calves, < 58 g/L of STP in dehydrated calves, and < 124 IU/L of GGT in calves with aged between 3 and 10 days. In nondehydrated diarrheic calves, the STP refractometer showed better diagnostic accuracy.In dehydrated calves aged between 3 and 10 days, however, its accuracy drops, and it is advisable to use GGT activity.

Relationship between refractive index and fatty acid composition by gas chromatography and near-infrared fiber-optic method in bovine fat.

The causes of the difference in fatty acid composition between gas chromatography (GC) and near-infrared fiber-optic method (NIR) in bovine fat and their countermeasures were studied using absolute values of refractive index. Using intermuscular fat from 45 crossbreeds, refractive index was measured by using a refractometer, and saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA) were measured by NIR and GC. The correlation coefficients between GC and NIR in SFA and MUFA, as well as those between refractive index and GC or NIR (in SFA and MUFA), were all greater than or equal to 0.8 (p < 0.01). In samples with 3% or more difference between GC and NIR in SFA and MUFA, GC and NIR values were often located in opposite directions to the regression lines with regard to refractive index. GC reanalysis on these samples slightly increased the correlation coefficient between GC and refractive index and reduced the difference between GC and NIR by 1%-2%. Results indicate that measurement errors in GC and NIR are related to their more than 3% difference, and GC reanalysis based on refractive index may improve its accuracy.

The impact of freezing and multiple freeze-thaw cycles on Brix refractometry estimates of immunoglobulin concentration in beef cattle colostrum.

Evaluation of immunoglobulin G (IgG) concentration in colostrum is important to guide on-farm management. Studies have shown that digital Brix refractometry accurately estimates colostrum IgG concentration in both dairy and beef cattle colostrum. Colostrum is often frozen in both clinical and research settings. The implications of this freezing on the accuracy of Brix refractometry measurements are largely unknown. The first objective of this study was to evaluate the agreement between digital Brix percentage measurements of IgG in beef cattle colostrum taken before and after different durations of freezing. The second objective was to evaluate the effects of multiple freeze-thaw (FT) cycles on Brix percentage measurements of IgG in beef cattle colostrum. There was good agreement between Brix percentages in fresh colostrum and after short (2 to 8 d), medium (4 to 7 mo), and long (3 y) periods of freezing (concordance correlation coefficient: 0.95, 0.96, and 0.96, respectively). Although there was no significant change in mean Brix percentages over 2 FT cycles (P > 0.05), mean Brix percentages decreased with 3 FT cycles (P = 0.017). Samples from the fourth and fifth FT cycles were observably coagulated, and these measurements were therefore deemed inaccurate. Data from this study indicate that freezing had minimal impact on digital Brix refractometer estimates of IgG concentration in beef cattle colostrum, but that samples stored for future testing should not undergo more than 2 FT cycles.

L'évaluation de la concentration d'immunoglobuline G (IgG) dans le colostrum est importante pour guider la gestion à la ferme. Des études ont montré que la réfractométrie Brix numérique estime avec précision la concentration d'IgG du colostrum dans le colostrum des bovins laitiers et de boucherie. Le colostrum est souvent congelé dans les milieux cliniques et de recherche. Les implications de cette congélation sur la précision des mesures de réfractométrie Brix sont largement inconnues. Le premier objectif de cette étude était d'évaluer la concordance entre les mesures numériques du pourcentage de Brix d'IgG dans le colostrum de bovins de boucherie prises avant et après différentes durées de congélation. Le deuxième objectif était d'évaluer les effets de plusieurs cycles de congélation-décongélation (FT) sur les mesures du pourcentage Brix d'IgG dans le colostrum de bovins de boucherie. Il y avait un bon accord entre les pourcentages de Brix dans le colostrum frais et après des périodes de congélation courtes (2 à 8 jours), moyennes (4 à 7 mois) et longues (3 ans) (coefficient de corrélation de concordance : 0,95, 0,96 et 0,96, respectivement). Bien qu'il n'y ait pas eu de changement significatif dans les pourcentages moyens de Brix sur deux cycles FT (P > 0,05), les pourcentages moyens de Brix ont diminué avec trois cycles FT (P = 0,017). Les échantillons des quatrième et cinquième cycles FT étaient coagulés de manière observable, et ces mesures ont donc été jugées inexactes. Les données de cette étude indiquent que la congélation a eu un impact minimal sur les estimations du réfractomètre numérique Brix de la concentration d'IgG dans le colostrum de les bovins de boucherie, mais que les échantillons stockés pour les tests futurs ne doivent pas subir plus de deux cycles FT.(Traduit par Docteur Serge Messier).

Diagnostic characteristics of refractometry cut-off points for the estimation of immunoglobulin G concentration in mare colostrum.

BACKGROUND: Feeding foals with poor quality colostrum predisposes them to failure of passive transfer (FPT). FPT is a major risk factor for neonatal infections. OBJECTIVES: To assess the optimal cut-offs for the optical (OR) and digital (DR) refractometer and determine their accuracy for poor quality colostrum diagnosis. STUDY DESIGN: A diagnostic validation study. METHODS: Eighty-one colostrum samples and sera were collected from broodmares and their neonatal foals, respectively. Colostral and serum IgG concentrations were measured by radial immunodiffusion (RID), DR and OR. Correlation coefficients were calculated. ROC curves were generated to identify optimal cut-offs for the refractometers and their diagnostic characteristics were evaluated. RESULTS: The optimal cut-offs for DR and OR were ≤23.75% and 23.9%, respectively. The sensitivity and specificity of the DR were 93.3% (95% CI: 66.0-99.7) and 87.9% (95% CI: 77.0-94.3) to detect colostral IgG <60 g/L, respectively. The sensitivity and specificity of the OR were 93.3% (95% CI: 66.0-99.7) and 81.8% (95% CI: 70.0-89.9), respectively. DR and OR had negative predictive values of 98.3% (95% CI: 89.7-99.9) and 98.2% (95% CI: 89.0-99.9), respectively, whilst positive predictive values were lower. No maternal variable, including breed, significantly influenced colostral IgG concentrations. Fifteen out of 81 colostrum samples had IgG <60 g/L. FPT and PFPT were diagnosed in 4/81 and 10/81 foals, respectively. Nine out of 14 animals with FPT/PFPT suckled colostrum with IgG <60 g/L. A moderate correlation (rs 0.542; P = .01) was observed between IgG concentrations measured by RID in sera and colostrum. MAIN LIMITATIONS: A smaller number of samples than the size requirement based on a priori estimate of specificity and the low prevalence of poor quality colostrum. CONCLUSIONS: The method has the potential to reliably differentiate between good and poor quality colostrum. Assessing colostrum quality by refractometry may be an indicator of passive transfer of immunity.

INTRODUCTION/CONTEXTE: Nourrir les poulains avec du colostrum de mauvaise qualité prédispose à l'échec du transfert d'immunité passive (FPT). FPT constitue un risque majeur pour les infections néonatales. OBJECTIFS: Évaluer les valeurs limites optimales au réfractomètre optique (RO) et digital (RD) et déterminer leur précision pour le diagnostic du colostrum de pauvre qualité. TYPE D'ÉTUDE: Étude de validation diagnostique. MÉTHODES: Quatre-vingt-un colostrums et sérums ont été recueillis à partir de juments de reproduction et de leur poulains nouveaux-nés respectivement. Les concentrations d'IgG dans le sérum et le colostrum ont été mesurées par immunodiffusion radiale (IDR), RO et RD. Les coefficients de corrélation ont été calculés. Des graphes d'air sous la courbe (ASC) ont été générés afin d'identifier les valeurs limites optimales aux différents réfractomètres et leurs caractéristiques diagnostiques ont été évaluées. RÉSULTATS: Les valeurs limites optimales pour les RD et RO étaient ≤23.75% et 23.9% respectivement. La sensibilité et la spécificité du RD étaient 93.3% (95% IC: 66.0-99.7) et 87.9% (95% IC: 77.0-94.3) pour la détection des IgG colostraux <6000 mg/dl, respectivement. La sensibilité et spécificité du RO étaient de 93.3% (95% IC: 66.0-99.7) et 81.8% (95% IC: 70.0-89.9), respectivement. Les RD et RO avaient une valeur prédictive négative de 98.3% (95% IC: 89.7-99.9) et 98.2% (95% IC: 89.0-99.9) respectivement, alors que les valeurs prédictives positives étaient plus basses. Aucune variable maternelle, incluant la race, n'a influencé significativement les concentrations colostrales en IgG. Quinze des 81 échantillons colostraux avaient une valeur d'IgG <6000 mg/dl. FPT et PFPT ont été diagnostiqué chez 4/81 et 10/81 poulains respectivement. Neuf des 14 animaux avec FPT/PFPT ont reçu du colostrum ayant des valeurs d'IgG <6000 mg/dl. Une corrélation modérée (rs 0.542; p= 0.01) a été observée entre les concentrations d'IgG mesurées par IDR dans le sérum et le colostrum. LIMITES PRINCIPALES: Le nombre d'échantillon est inférieur à celui recommandé basé sur unestimé a priori de la spécificité et considérant la faible prévalence de colostrum de pauvre qualité. CONCLUSIONS: La méthodologie utilisée pourrait différencier de façon fiable les colostrums de pauvre et bonne qualité. L'évaluation de la qualité du colostrum par réfractométrie pourrait représenter un indice du transfert d'immunité passive.

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.

Diagnostic accuracy of refractometry methods for estimating passive immunity status in neonatal beef calves.

BACKGROUND: Assessing the inadequate transfer of passive immunity (ITPI) in beef calves is crucial because calves with ITPI are at high risk for morbidity and mortality. OBJECTIVES: The aim of this study was to determine the accuracy of digital Brix (D-BRIX) and digital serum total protein (D-STP) refractometers to estimate different passive immunity status in beef calves and to determine the robustness of thresholds. METHODS: Blood samples were collected from 202 (1-7 days old) beef calves. Serum total solid percentages, total protein concentrations, and IgG concentrations were measured with the D-BRIX refractometer, D-STP refractometer, and gold standard radial immunodiffusion (RID) assay, respectively. Data were analyzed using diagnostic test accuracy, areas under the receiver operating characteristics curve, Cohen's kappa coefficient, and misclassification costs analysis to estimate IgG concentrations <10, <16, and <24 mg/mL. RESULTS: For the prediction of serum IgG concentrations <10, <16 and <24 mg/mL, the optimal cut-off values were determined to be <8.5% (Se: 100.0% (95% CI: 87.9-100.0); Sp: 94.2% [95% CI: 89.6-97.2]), <8.5% (Se: 92.1% [95% CI: 78.6-98.2]; Sp: 97.6% [95% CI: 93.9-99.3]), and <10.1% (Se: 88.8% [95% CI: 79.7-94.7]; Sp: 67.2% [95% CI: 58.1-75.4]), respectively, for the D-BRIX refractometer; and <5.2 g/dL (Se: 100.0% [95% CI: 87.9-100.0]; Sp: 93.6% [95% CI: 88.9-96.8]), <5.2 g/dL (Se: 92.1% [95% CI: 78.6-98.2]; Sp: 97.0% [95% CI: 93.0-99.0]), and <6.4 g/dL (Se: 87.5% [95% CI: 78.2-93.8]; Sp: 69.7% [95% CI: 60.7-77.7]), respectively, for the D-STP refractometer. CONCLUSIONS: The digital Brix and digital serum total protein refractometers can be used as monitoring tools for assessing passive immunity transfer in neonatal beef calves.

Evaluation of 2 refractometers to estimate different passive immunity status in Simmental dairy calves.

Inadequate transfer of passive immunity (ITPI) is major risk for mortality, morbidity and decreased growth performance in dairy and beef calves. Refractometry method is used in estimating ITPI in dairy and beef calves but studies evaluating refractometers for Simmental dairy calves are limited. The objectives of this study were determining the accuracy of digital serum total protein refractometer (STP-REF) and digital Brix refractometer (BRIX-REF) in the estimating of different passive immunity status (<10, <18, <25 and <32 g/L) in Simmental dairy calves. Serum samples were collected from apparently healthy Simmental dairy calves aged 1-8 days (n = 291). Serum total solid percentages were measured using BRIX-REF, serum total protein concentrations were measured using STP-REF and serum IgG concentrations were measured using radial immunodiffusion (RID) assay as a reference test. Correlation coefficients were calculated between RID test and refractometers results, and each other. The diagnostic test performance of the refractometers at IgG concentrations of < 10, < 18, < 25 and < 32 g/L was measured by performing a receiver operating characteristics (ROC) analysis. The optimal thresholds of the refractometers were determined based on Youden's J statistics and after accounting for different costs between false positive and false negative cases using misclassification cost term analysis. The overall test performance and the agreement of the refractometers were assessed using area under the ROC curve and Cohen's kappa analysis. Optimal thresholds were determined as < 7.9, < 8.3, < 8.7, < 9.4% for the BRIX-REF, and < 4.6, < 5.2, < 5.4, < 5.8 g/dL for the STP-REF in estimating IgG concentrations of < 10, < 18, < 25, < 32 g/L, respectively. Se and Sp of BRIX-REF were 88.8% and 89.1% for < 7.9% Brix, 81.6% and 94.2% for < 8.3% Brix, 77.9% and 97.4% for < 8.7% Brix and 81.7% and 91.2% for < 9.4% Brix, respectively. Se and Sp of STP-REF 92.5% and 88.2% for < 4.6 g/dL; 92.1% and 87.1% for < 5.2 g/dL; 81.7% and 93.6% for < 5.4 g/dL; 79.0% and 94.1% for < 5.8 g/dL, respectively. Both, digital Brix and STP refractometers performed well to estimate the status of passive immunity in dairy Simmental calves.

Genetic parameters of colostrum and calf serum antibodies in Swedish dairy cattle.

BACKGROUND: A sufficient IgG content in the colostrum is essential for the newborn calf, as it provides passive immunity which substantially affects the probability of survival during rearing. Failure of passive transfer (FPT) occurs when a calf does not absorb enough antibodies from the colostrum and is defined by an IgG concentration in calf serum lower than 10 g/L. Apart from delayed access to colostrum, FPT can be due to a low production of IgG in the mother or poor IgG absorption by the calf. The aim of this study was to estimate the genetic background of antibody levels and indicator traits for antibodies in the colostrum and calf serum, and their correlation with milk production. RESULTS: Colostrum data were available for 1340 dairy cows with at least one calving and calf serum data were available for 886 calves from these cows. Indicator traits for antibody concentrations were estimated using refractometry (a digital Brix refractometer for colostrum and an optical refractometer for serum), and enzyme-linked immunosorbent assays (ELISA) were used to determine the levels of total IgG and natural antibodies (NAb) of various antibody isotypes in the colostrum and calf serum. Colostrum traits had heritabilities ranging from 0.16 to 0.31 with repeatabilities ranging from 0.21 to 0.55. Brix percentages had positive genetic correlations with all colostrum antibody traits including total IgG (0.68). Calf serum antibody concentrations had heritabilities ranging from 0.25 to 0.59, with a significant maternal effect accounting for 17 to 27% of the variance. When later in life calves produced their first lactation, the lactation average somatic cell score was found to be negatively correlated with NAb levels in calf serum. CONCLUSIONS: Our results suggest that antibody levels in the colostrum and calf serum can be increased by means of selection.

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.

Diagnostic accuracy of digital Brix and serum total protein refractometers in estimating different passive immunity levels in dairy calves.

The aim of this study was to determine the diagnostic accuracy of digital serum total protein (TP) and digital Brix refractometers in estimating different passive immunity levels (<10, <18, <25 mg/mL) in dairy calves. Blood samples were collected from 260 apparently healthy Holstein calves, aged 2-7 days. Serum IgG concentrations were measured using digital Brix and TP refractometers and the radial immunodiffusion (RID) assay, as the gold standard. Data were analyzed by a receiver operating characteristics (ROC) analysis, the area under the ROC curves (AUC) and Cohen's kappa (κ). Optimal thresholds were determined as < 8.4, < 9.0 and < 9.4% for the digital Brix refractometer, and < 5.0, < 5.4 and < 5.8 g/dL for the serum TP refractometer in estimating IgG concentrations of < 10, < 18, < 25 mg/mL, respectively. The sensitivity (Se) and specificity (Sp) of the Brix refractometer were 96.3% and 88.8% for < 8.4% Brix, 97.0% and 83.4% for < 9.0% Brix, and 85.5% and 77.8% for < 9.4% Brix, respectively. The Se and Sp of the serum TP refractometer were 96.3% and 90.1% for < 5.0 g/dL, 91.0% and 89.6% for < 5.4 g/dL, 79.6% and 85.2% for < 5.8 g/dL, respectively. The discriminant ability of the refractometers was moderately accurate in estimating IgG concentrations of < 10 and < 18 mg/mL, and highly accurate in estimating IgG concentrations of < 25 mg/mL. Both refractometers substantially agreed with RID-IgG results and almost perfectly agreed with each other. In conclusion, the digital Brix and digital serum TP refractometers offer a good utility for determining different passive immunity levels in dairy calves.

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.

Associations between the metabolic status of the cow and colostrum quality as determined by Brix refractometry.

Supplying newborn calves with immunoglobins is critical for their health and a daily challenge in the dairy industry. Among various factors determining colostrum quality, the prepartum metabolic status of the cow might be of particular importance. The objective of this observational cross-sectional study was to evaluate relationships between cow-level variables and the colostrum quality as determined by Brix refractometry. A total of 873 cows of varying breed and parity from 124 German dairy herds were included in the study, and blood and urine samples were taken 3 to 1 wk before the expected calving date. Effectively, samples were collected on average 8.2 d (geometric mean) before calving, ranging from 2 to 45 d. The final variable set included body condition score, lameness score, breed, parity, vaccination of the cow, the activity of glutamate dehydrogenase and aspartate aminotransferase, the urine concentration of creatinine, net acid-base excretion, the serum concentration of cholesterol and calcium, and the difference in albumin and total protein concentration. Generalized linear mixed effects regression models with hierarchically structured random effects (cow within herd) using the maximum likelihood method were fitted to the data to identify associations between the Brix value as an outcome and cow-level variables as predictors. Cows entering second parity had lower Brix values compared with cows entering third or greater parity, and prepartum vaccination of cows led to higher Brix values compared with nonvaccinated cows. Cows with a moderate to high lameness score had lower Brix values than cows with low-grade lameness. An increase of glutamate dehydrogenase serum activity and serum calcium concentration were associated with lower Brix values, whereas an increase in the difference of total protein and albumin serum concentration led to higher Brix values. In conclusion, the metabolic health of the cow affects colostrum quality and may cause failure of passive immunoglobulin transfer as well as impaired calf health.