Evaluation of Brix Refractometry to Estimate Immunoglobulin G Content in Buffalo Colostrum and Neonatal Calf Serum

SIMPLE SUMMARY: The protective effects of colostrum in relation to the incidence and severity of newborn ruminant diseases are well established. Neonatal calf depends on the timely supply of high-quality colostrum to prevent the failure of passive transfer of immunoglobulins (Ig), which has been linked to increased risk of different diseases and mortality in early stages of life. Despite the relevance of Buffaloes (Bubalus Bubalis) in world dairy production, the available knowledge regarding colostrum quality management remains scarce for this species. Therefore, the objective of this study was to evaluate the utility of a simple and rapid tool such as a digital Brix refractometer to estimate colostrum quality and for predicting the success of passive transfer of immunoglobulin G (IgG) in Buffalo calves. For this aim, correlation analysis was performed between Brix results and ELISA-IgG determination from colostrum and serum samples. A strong correlation was found between Brix measurements and IgG content in colostrum and serum samples. Moreover, cut point values for Brix measurements for colostrum and serum samples were determined. Brix refractometry was found to be an acceptable tool for on-farm estimations of colostrum quality and passive immunity transfer (PIT) in Buffalo calves. ABSTRACT: Brix refractometry has been widely demonstrated to be a useful tool for monitoring colostrum management program and passive immunity transfer (PIT) in Bovines, but its suitability has never been verified in Buffalo. Therefore, the objective of this study was to evaluate the utility of a simple and rapid tool such as a digital Brix refractometer to estimate colostrum quality and for evaluating the success of passive transfer of immunoglobulin G (IgG) in Buffalo calves. The optimal cut points levels for Brix Refractometry for distinguishing good- and poor-quality colostrum and for assessing the adequacy of passive immunity transfer in calves were determined. For this aim, 26 first-milking maternal colostrum (MC) were collected from first-calf heifers. Blood samples were obtained from their calves at birth (T0) and 72 hours after (T3). Colostrum and Serum IgG content were determined by indirect enzyme-linked immunosorbent assay (ELISA), whereas total protein (TP, g/dL) and percentage Brix (%Brix) by means of a digital Brix refractometer. The mean colostrum IgG was 64.9 ± 29.3 mg/mL. The mean serum %Brix at T3 was 9.6 ± 0.9 %. The mean serum IgG content at T3 was 11.1 ± 2.0 mg/mL. Pearson’s correlation coefficient (r(p)) was determined between Brix and ELISA measurements: colostrum %Brix showed a significant correlation with serum %Brix (r(p) = 0.82, p < 0.001); serum %Brix was highly correlated with serum TP (STP, g/dL) (r(p) = 0.98, p < 0.001) and serum IgG (mg/mL) (r(p) = 0.85, p < 0.001). A cut point of 18% Brix to estimate samples of MC ≥ 50 mg/mL from first-calf heifers was more appropriate for the buffalo. A cut point of 8.4% Brix resulted in the greatest percentage of calf serum samples being correctly classified. Based on our findings, a digital Brix refractometer could be a useful tool to monitor colostrum quality and to estimate PIT in Buffalo calves.