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.

Colostrum Quality Assessment in Dairy Goats: Use of an On-Farm Optical Refractometer

“…On day 2 and 3 postpartum, IgG values were reduced to 22.4 and 8.4 mg/mL, respectively, in agreement with other published results [ 10 ]. A significant reduction in IgG in goat colostrum during postpartum was observed, similar to that previously described using a colostrometer [ 10 ]. Our study demonstrates that not all the goats have enough IgG content after parturition, as about 10% of the animals in the present study showed values below the optimal threshold, set over 20 mg/mL according to previous studies [ 17 , 18 ].…”

“…In the present trial, the average concentrations of IgG in goat colostrum measured by ELISA on day 1 post-kidding reached 36.6 mg/ml, being lower than those described in some of the previous studies (50.0 mg/mL [ 18 ], 54.4 mg/mL [ 9 ] or 73.67 mg/mL [ 11 ]), but higher than others (10.6 mg/mL [ 10 ]). On day 2 and 3 postpartum, IgG values were reduced to 22.4 and 8.4 mg/mL, respectively, in agreement with other published results [ 10 ]. A significant reduction in IgG in goat colostrum during postpartum was observed, similar to that previously described using a colostrometer [ 10 ].…”

“…Recent studies in goats report that optical refractometry is a good option for the assessment of colostrum quality, and no differences are observed compared to digital refractometers [ 14 ]. This work enables the establishment of a cut-off threshold for characterizing good-quality colostrum at around 18.5–21.5% [ 10 , 13 , 17 ]. In other cases, farmers may be interested in determining the colostrum quality of nursing goats—i.e., goats at day 2 or 3 post-partum that are milked to obtain colostrum, which will be frozen to feed orphaned kids.…”

“…The literature describes different methods for the determination of IgG in goats colostrum such as RIA, electrophoresis, radial immunodiffusion (RID) or enzyme-linked immunosorbent assay (ELISA) [ 6 , 7 ], and on-farm tests to estimate the IgG values, as colostrometers, refractometers or color evaluation [ 8 , 9 ]. Around 24 h after parturition, IgG levels in goat colostrum have been reported to range from 10.6 mg/mL [ 10 ] to 73.7 mg/mL [ 11 ]. Currently, RID and ELISA tests are the most widely used and accurate methods for measuring the IgG concentration of colostrum [ 12 , 13 ].…”

“…There are few studies prospecting the use of refractometers to assess colostrum quality in goats, in contrast to the abundant scientific reports carried out in bovines [ 1 , 14 , 15 , 16 , 17 ]. Recently, optical and digital refractometers have been deployed for the estimation of IgG in goat colostrum [ 10 , 13 , 18 ]; these offer multiple advantages inasmuch as they are low-cost, rapid, easy and practical for on-farm application. Moderate and strong correlation has been reported in goat colostrum for IgG assessment by ELISA and the Brix values (total soluble solids) by refractometry [ 12 , 14 , 17 ].…”