Abstract
There are few published data on the accurate on-farm diagnosis of failure of transfer of passive immunity (FTPI) in beef–suckler calves. This observational study aimed to evaluate the diagnostic performance and differences among four types of refractometers for assessing FTPI in Chianina beef–suckler calves. Blood samples were collected from 85 Chianina calves aged 2–7 days. The serum immunoglobulin G (IgG) concentration was measured using radial immunodiffusion (RID), digital and optical serum total protein (STP) refractometers, and digital and optical serum refractometers. The diagnostic performance of the refractometers was determined based on the serum IgG threshold of 16 g/L (measured by RID). A receiver operating characteristic (ROC) curve was used to identify the optimal cutoff values for all refractometers. The RID IgG concentration was positively correlated with all four refractometers (correlation coefficient: 0.75–0.84). ROC analysis yielded optimal cutoff values for predicting FTPI of 51 g/L (sensitivity (Se)=0.63 and specificity (Sp)=0.96) and 52 g/L (Se = 0.69 and Sp = 0.90) for the digital and optical STP refractometers, respectively. At the threshold of 8.3% Brix, the Se and Sp were 0.66 and 0.92 for the optical Brix and 0.77 and 0.92 for the digital Brix refractometer, respectively. All four refractometers were useful for assessing FTPI in Chianina calves. However, the digital Brix had the highest combined diagnostic accuracy for FTPI. The on-farm use of refractometers to assess FTPI can become part of routine monitoring of the colostrum management program in beef–suckler calf herds. Highlights The cutoff values were 51 and 52 g/L for the digital and optical serum total protein refractometers, respectively. The digital Brix refractometer was the most accurate for the detection of calves with inadequate transfer of passive immunity.
Highlights
Failure of transfer of passive immunity (FTPI) occurs when a calf fails to absorb an adequate quantity of colostral passive immunity
The results of our investigation show that the serum total protein (STP) concentration and %Brix as evaluated by the digital refractometers had the highest correlation with immunoglobulin G (IgG) obtained by radial immunodiffusion (RID) in assessing the transfer of passive
An in-depth evaluation of the FTPI in the Chianina population was beyond the scope of this study due to the low number of samples, the results showed that the calves with a negative screening test were correctly classified by the digital and optical refractometers in different FTPI prevalence scenarios
Summary
Failure of transfer of passive immunity (FTPI) occurs when a calf fails to absorb an adequate quantity of colostral passive immunity. This condition is highly correlated with the health of calves and, with the productivity of the farm (Raboisson et al 2016). Several direct and indirect methods have been used to monitor passive immunity transfer in calves. Radial immunodiffusion (RID) is considered the gold standard for determining the immunoglobulin G (IgG) concentration in calf serum but requires a specialised laboratory, and the results are not available immediately (Morrill et al 2013). The tools more commonly used are the Brix refractometer, which approximates the percentage of the total solids (%Brix) in liquids, and the serum total protein refractometer, which is used to evaluate the serum total protein (STP; g/L) concentration
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