Validation of Brix refractometer to estimate immunoglobulin G concentration in goat colostrum

Abstract

Background and Aim: Immunoglobulin G (IgG) concentration is high in goat colostrum, particularly in the first few hours after parturition, and this is important for the kid's immunity and growth. IgG levels vary depending on several factors, including breed, disease status, colostrum management, handling, and collection time postpartum. A handheld optical refractometer, an affordable instrument that is simple to use in the field, is used widely in dairy farms to measure total solids. However, it can also be applied to estimate colostrum IgG content on the basis of comparison with standard measurement methods, usually radial immunodiffusion. Studies comparing %Brix values in relation to IgG concentration measured using enzyme-linked immunosorbent assay (ELISA) in goats are limited. The present study aimed to evaluate the use of a handheld optical Brix refractometer for the measurement of IgG concentration in goat colostrum, compare results with those using ELISA, and estimate the %Brix cutoff value equating to low-quality colostrum. Materials and Methods: Colostrum samples were collected on day 0 from 21 goats (nine Black Bengal, six Saanen, and six of their crossbred offspring) and were frozen. Subsequently, they were analyzed for IgG concentration using a goat-specific ELISA test and Brix percentage using a handheld refractometer. The optimum %Brix cutoff value for the evaluation of colostrum quality was evaluated. Results: The mean IgG concentration and %Brix in colostrum were 10.60±0.64 and 25.0±0.9 mg/mL, respectively. There was a significant (p<0.01) correlation between %Brix and IgG concentration. For an IgG concentration of 6.9 mg/dl, the cutoff value for %Brix was 18.5, equating to high specificity (100%) but low sensitivity (50%). A higher %Brix cutoff value of 21.5 showed high specificity (95%) and high sensitivity (100%). Conclusion: A Brix refractometer can be used to estimate goat colostrum quality with a proposed %Brix cutoff value of <18.5%-21.5% for poor-quality colostrum.