Evaluation of 3 refractometers to determine transfer of passive immunity in neonatal beef calves

Abstract

Background: Refractometry is used to assess transfer of passive immunity (TPI), but studies evaluating different refractometers and appropriate thresholds for recommended target immunoglobulin G (IgG) concentrations for beef calves are limited. Objectives: To evaluate test performance of digital (DSTP) and optical (OSTP) serum total protein (STP) refractometers and a digital Brix (DBRIX) refractometer for assessment of passive immunity in beef calves. Animals: A total of 398 beef calves from 6 herds, 1 to 7 days of age. Methods: Serum IgG concentration was estimated by DSTP, OSTP, and DBRIX, and measured by radial immunodiffusion (RID). Correlation coefficients (r) among results were calculated. Optimal STP and Brix thresholds for identification of IgG <10, <16, and <24 g/L were determined using interval likelihood ratios. Refractometer performance and agreement were assessed using areas under the curve (AUC), diagnostic test characteristics, Cohen's kappa (κ), and Bland-Altman analysis. Results: Refractometer results were highly correlated with RID (r = 0.82-0.91) and with each other (r = 0.91-0.95), and overall test performance was excellent (AUC = 0.93-0.99). The STP concentrations of ≤5.1, ≤5.1, and ≤5.7 g/dL and Brix percentages of ≤7.9%, ≤8.3%, and ≤8.7% indicated IgG concentrations <10, <16, and <24 g/L, respectively. Agreement of refractometers with RID was variable (κ = 0.46-0.80) and among refractometers was substantial (κ = 0.62-0.89). Conclusions and Clinical Importance: All refractometers showed good utility as monitoring tools for assessment of TPI in beef calves.

An Assessment of the Accuracy of Digital and Optical Brix Refractometers for Estimating Passive Immunity in Beef Calves

“…The optimal cut-off value we ascertained in the present study for the D-Brix refractometer for the estimation of IgG concentrations of <16 g/L was similar to previously reported digital Brix percentages for IgG of <16 g/L (Gamsjäger et al, 2021;Pisello et al, 2021;Akköse et al, 2022c). The cut-off value we determined for the D-Brix refractometer for estimating IgG concentrations of <24 g/L was higher than the digital Brix refractometer cut-off value previously reported by Gamsjäger et al (2021) and lower than the digital Brix refractometer cut-off value previously reported by Akköse et al (2022c). The cut-off value ascertained for the O-Brix refractometer for estimating IgG concentrations of <16 g/L was similar to the optical Brix refractometer cut-off value reported by Pisello et al (2021).…”

“…Our study compared the diagnostic accuracy of optical and digital Brix refractometers in predicting different passive immunity statuses in beef calves. To date, only very few studies have assessed digital Brix percentages indicative of serum IgG of <16 g/L (Gamsjäger et al, 2021;Pisello et al, 2021;Akköse et al, 2022c) or <24 g/L (Gamsjäger et al, 2021;Akköse et al, 2022c). On the other hand, there is no report on optical Brix percentages indicative of serum IgG of <24 g/L.…”

“…It is also possible to use Brix refractometers in determining colostrum quality (Buczinski et al, 2016). While a large number of comparative studies are available on the utility and performance of refractometers in diagnosing ITPI in dairy calves (Buczinski et al, 2021;Akköse et al, 2022a:b), there are only very few studies that have evaluated refractometry methods for the assessment of passive immunity status in beef calves (Vandeputte et al, 2011;Todd et al, 2018;Gamsjäger et al, 2021;Pisello et al, 2021;Akköse et al, 2022c). This study aimed at determining and comparing the diagnostic accuracy of digital and optical Brix refractometers for the prediction of different passive immunity statuses in beef calves, and at demonstrating the correlation and agreement level of the results achieved with these refractometers.…”

The titers, duration, and residual clinical protection of passively transferred nasal and serum antibodies are similar among beef calves that nursed colostrum from vaccinated or unvaccinated dams and were challenged experimentally with bovine respiratory syncytial virus at three months of age

“…26 Similarly, the median serum Brix of calves at 48 hours of life (NO-VACC, 10.9%; VACC, 10.6%) was adequate and consistent with what is considered excellent transfer of passive immunity in beef calves. 27 Results from previous studies 28,29 have demonstrated that the greater the initial virus-specific serum antibody titer transferred from colostrum, the longer the duration of specific immunity in calves. Other studies 30,31 suggest that vaccination of cows during the last trimester of gestation with inactivated-virus vaccines results in greater deposition of specific antibodies in maternal colostrum and greater initial BVDV and BHV-1 serum antibody titers in their calves.…”

Assessment of a Rapid Semi-Quantitative Immunochromatographic Test for the Evaluation of Transfer of Passive Immunity in Calves

“…Only the performances for the category of poor TPI could be directly compared with other studies using a dichotomous standard with cut-off value equivalent to 10 mg/mL IgG. The sensitivity of the Brix refractometer for this category (0.69) was lower than that reported in many other studies in the literature (e.g., 0.87 [27], 0.88 [18], 0.81 [45]). One reason might be the different Brix cut-off values in these studies that were usually optimized (e.g., using ROC curves) to obtain the best results.…”