Abstract
BackgroundEstimation of the quantity of colostral IgG or serum IgG absorbed following ingestion of colostrum by calves is essential for monitoring the effectiveness of colostrum feeding practices on dairy farms. Milk total solids concentrations determination is a critical part of quality assessment of nonsaleable whole milk prior to feeding to calves. To date, on-farm methods to assess colostral IgG, serum IgG or milk total solids concentrations have been performed separately with various instruments. The objective of this study was to evaluate the diagnostic performance of a single electronic, hand-held refractometer for assessing colostral and serum IgG concentrations and milk total solids in dairy cattle. Colostral IgG, serum IgG and milk total solids concentrations were determined by the refractometer. Corresponding analysis of colostral and serum IgG concentrations were determined by radial immunodiffusion (RID) while milk total solids were determined by spectrophotometry. Sensitivity and specificity of the refractometer for colostrum and serum samples were calculated as determined by RID. Sensitivity and specificity of the refractometer for milk samples was calculated as determined by spectrophotometry.ResultsThe sensitivity of the refractometer was 1 for colostral IgG, serum IgG and milk total solids determinations. Specificity of the refractometer was 0.66, 0.24 and 0 for colostral IgG, serum IgG and milk total solids determinations, respectively. The refractometer underestimated colostral IgG, serum IgG and milk total solids concentrations compared to the concentrations determined by RID or spectrophotometry.ConclusionsThe refractometer was an acceptable, rapid, convenient on-farm method for determining colostral IgG and milk total solids. The refractometer was not an acceptable method for determination of serum IgG concentrations as it severely underestimated the serum IgG concentrations.
Highlights
Estimation of the quantity of colostral IgG or serum IgG absorbed following ingestion of colostrum by calves is essential for monitoring the effectiveness of colostrum feeding practices on dairy farms
The purpose of this study was to evaluate the practical diagnostic utility of a single on-farm refractometer capable of estimating colostral or serum IgG concentrations and milk total solids with test results reported in g/L for colostrum and serum and % total solids for milk
Mean bias based on the Bland-Altman plots was 11.3 g/L (95% limits of agreement, -0.2-22.8) indicating that the refractometer underestimated sample serum IgG concentrations by 11.3 g/L, on average
Summary
Estimation of the quantity of colostral IgG or serum IgG absorbed following ingestion of colostrum by calves is essential for monitoring the effectiveness of colostrum feeding practices on dairy farms. Several on-farm methods for estimating colostral IgG concentrations have been reported including hydrometers [1,2], weight of first milking colostrum [3], immunoassay [4], and electronic refractometer [5] with variable test sensitivity and levels of practical application. Estimation of the quantity of IgG absorbed following ingestion of colostrum by calves is essential for monitoring the effectiveness of colostrum feeding practices on dairy farms. Practical methods used for estimating serum IgG following ingestion of colostrum in dairy calves include serum total protein determination by refractometry [6,7], sodium sulfite [8], and turbidimetric methods [9]. Practical methods used to assess whole milk total solids in dairy milk include refractometry [11,12] while spectrophotometry is considered the reference method for evaluating milk total solids [12]
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