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Assessment of Brix refractometry to estimate immunoglobulin G concentration in beef cow colostrum
Lisa Gamsjäger1, Ibrahim Elsohaby2,3, Jennifer M Pearson1
1Department of Production Animal Health, University of Calgary Faculty of Veterinary Medicine, Calgary, Alberta, Canada.
Insights
Brix refractometry accurately estimates beef cow colostrum immunoglobulin G (IgG) levels, with optimal thresholds of <24% for low IgG and ≥30% for high IgG. This method shows reliable interlaboratory agreement for farm use.
Area of Science:
- Veterinary Medicine
- Animal Science
- Ruminant Nutrition
Background:
- Assessing colostral immunoglobulin G (IgG) concentration is crucial for calf health.
- Brix refractometry offers a potential method for estimating IgG, but specific thresholds for beef cows and interlaboratory agreement are not well-established.
Purpose of the Study:
- To evaluate the performance and interlaboratory agreement of Brix refractometry for estimating IgG in beef cow colostrum.
- To determine optimal Brix percentage thresholds for identifying colostrum with IgG concentrations below 100 g/L and above 150 g/L.
Main Methods:
- Retrospective study involving 416 beef cows from 11 operations in Alberta, Canada.
- Colostral IgG concentrations measured by radial immunodiffusion (RID) and estimated using Brix refractometry.
- Statistical analyses included Spearman correlation, likelihood ratios, cost-term analysis, concordance correlation coefficient (CCC), and Bland-Altman analysis across three laboratories.
Main Results:
- Brix refractometry showed strong positive correlations with IgG concentrations (r = 0.68–0.76) across laboratories.
- Optimal Brix thresholds were identified as <24% for IgG <100 g/L and ≥30% for IgG ≥150 g/L.
- Substantial interlaboratory agreement was observed (CCC = 0.89–0.96) with minimal mean differences and narrow limits of agreement.
Conclusions:
- Brix refractometry is a reliable tool for estimating IgG concentrations in beef cow colostrum.
- The identified Brix thresholds can aid in making informed colostrum management decisions on farms.
- The method demonstrates consistent performance across different laboratories, supporting its practical application.
Background:
Brix refractometry can be used to assess colostral immunoglobulin G (IgG) concentration, but studies identifying Brix percentages to detect high- and low-IgG colostrum are lacking for beef cows and interlaboratory agreement is unknown.
Objectives:
Evaluate Brix refractometer performance and interlaboratory agreement for assessing beef cow colostrum IgG concentration, including determination of thresholds to identify colostrum containing IgG concentrations <100 g/L and ≥150 g/L.
Animals:
Beef cows (n = 416) from 11 cow-calf operations in Alberta, Canada.
Methods:
Colostral IgG concentrations were measured using radial immunodiffusion (RID) and estimated by Brix refractometry for this retrospective study. Spearman correlation coefficients were assessed between RID and Brix refractometry. Likelihood ratios and misclassification cost-term analysis were used to determine optimal Brix percentages for detecting colostrum containing IgG concentrations <100 g/L and ≥150 g/L. Concordance correlation coefficient (CCC) and Bland-Altman analyses were performed for Brix percentages obtained at 3 different laboratories.
Results:
Brix percentages obtained at 3 laboratories were positively correlated with IgG results (r = 0.72, 0.68, and 0.76, respectively). Colostrum Brix percentages of <24% and ≥30% were optimal for indicating IgG concentrations of <100 g/L and ≥150 g/L, respectively. Interlaboratory agreement was substantial, with CCC ranging from 0.89 to 0.96 and Bland-Altman analysis showing small mean differences (-1.2% to 0.09% Brix) and narrow limits of agreements (-4.8% to 2.4% Brix) among laboratories.
Conclusions And Clinical Importance:
Brix refractometry shows good potential for reliably estimating IgG concentrations in beef cow colostrum across multiple laboratories and can be recommended to aid colostrum management decisions on farms.
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