Diagnostic characteristics of refractometry cut-off points for the estimation of immunoglobulin G concentration in mare colostrum.
Authors: Rampacci Elisa, Mazzola Karen, Beccati Francesca, Passamonti Fabrizio
Journal: Equine veterinary journal
Summary
# Editorial Summary: Refractometry Cut-offs for Equine Colostrum Quality Assessment Failure of passive transfer (FPT) remains a significant threat to neonatal foal health, and poor-quality colostrum is a primary risk factor. Rampacci and colleagues validated digital and optical refractometry as screening tools by comparing refractometer readings against radial immunodiffusion measurements in 81 colostrum samples and corresponding foal sera, using receiver operating characteristic curve analysis to establish optimal cut-off thresholds. Both refractometers demonstrated excellent negative predictive values (98.3% for digital, 98.2% for optical) at cut-off points of ≤23.75% and ≤23.9% respectively, with sensitivity and specificity around 93% and 82–88%—meaning they reliably rule out poor-quality colostrum when readings exceed these thresholds. In the cohort, 15 of 81 samples had IgG below 60 g/L, and nine of the 14 foals diagnosed with FPT or partial FPT had consumed such low-IgG colostrum, highlighting the clinical relevance of pre-suckling assessment. For practitioners, these findings support rapid refractometer screening as a practical, field-based method to identify at-risk mares and foals before passive transfer failure occurs, though the moderate correlation between colostral and serum IgG suggests refractometry is best used as an indicator rather than a definitive predictor of individual foal immunity status.
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Practical Takeaways
- •Refractometry is a practical field-applicable tool to quickly identify poor quality colostrum and prevent failure of passive transfer in foals; digital refractometers perform slightly better than optical ones
- •A refractometer reading of ≤23.75% indicates poor quality colostrum requiring intervention, while readings above this threshold are highly reliable for confirming adequate passive immunity transfer
- •Using refractometry to assess colostrum quality before foals nurse can identify at-risk neonates early and guide supplementation decisions to prevent serious neonatal infections
Key Findings
- •Optimal refractometer cut-offs for detecting poor quality colostrum (IgG <60 g/L) were ≤23.75% for digital refractometer and 23.9% for optical refractometer
- •Digital refractometer showed 93.3% sensitivity and 87.9% specificity; optical refractometer showed 93.3% sensitivity and 81.8% specificity for detecting colostral IgG <60 g/L
- •Both refractometers demonstrated high negative predictive values (98.3% and 98.2%) making them reliable for ruling out poor quality colostrum
- •9 of 14 foals with FPT/PFPT had consumed colostrum with IgG <60 g/L, and moderate correlation (rs 0.542) existed between colostral and serum IgG concentrations