title: Assessment of different methods to estimate bovine colostrum quality on farm.
abstract: OBJECTIVE
  To evaluate two different hydrometers and an optical and a digital Brix refractometer for the assessment of bovine colostrum quality, in terms of accuracy and precision compared with the measurement of IgG concentrations using radial immunodiffusion (RID), and to evaluate the reliability and repeatability of the Brix refractometers.
  
  
  METHODS
  To determine reliability and repeatability, 145 colostrum samples were tested by two independent observers twice, using the optical and digital Brix refractometers. A further 193 colostrum samples from Holstein cows were collected on one commercial dairy farm at first milking and tested with two hydrometers and an optical and digital Brix refractometer. An aliquot of each sample was frozen for RID measurement of IgG concentrations and samples were classified as poor (≤50 g IgG/L) or good (>50 g IgG/L) quality colostrum. Intraclass correlation coefficients (ICC) were used to determine inter- and intra-observer reliability and repeatability. Optimised cut-off values for the four devices were determined using receiver operating characteristics (ROC) analysis with the RID results as the reference. Using these cut-offs, sensitivities and specificities for determining good quality colostrum were calculated.
  
  
  RESULTS
  The ICC for inter-observer reliability was 0.98 for the optical Brix refractometer, and for intra-observer repeatability was 0.97 and 0.98 for the optical and the digital Brix refractometers, respectively. For the 193 colostrum samples, 67 (34.7%) had concentrations of IgG ≤50 g/L determined by RID. Optimised cut-off values evaluated by ROC analysis were higher for all devices compared with manufacturer reference or previously published values. Using these values, the sensitivities for the two hydrometers, and the optical and the digital Brix refractometers were 0.73, 0.71, 0.56 and 0.79, respectively; specificities were 0.72, 0.61, 0.90 and 0.69, respectively.
  
  
  CONCLUSIONS
  The Brix refractometers provided the most accurate assessment of colostrum quality of the devices evaluated, and demonstrated excellent precision in terms of repeatability. To provide optimal health for newborn calves, a sufficient intake of good quality colostrum is essential. The Brix refractometers provide rapid, convenient tools for classification of colostrum quality.
authors.affiliation: a Clinical Unit for Herd Health Management in Ruminants , University Clinic for Ruminants, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna , Veterinaerplatz 1, 1210 Vienna , Austria.
authors.forename: M-C
authors.initials: MC
authors.lastname: Bartens
authors.affiliation: a Clinical Unit for Herd Health Management in Ruminants , University Clinic for Ruminants, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna , Veterinaerplatz 1, 1210 Vienna , Austria.
authors.forename: M
authors.initials: M
authors.lastname: Drillich
authors.affiliation: b Institute of Milk Hygiene, Milk Technology and Food Science , Veterinaerplatz 1, 1210 Vienna , Austria.
authors.forename: K
authors.initials: K
authors.lastname: Rychli
authors.affiliation: a Clinical Unit for Herd Health Management in Ruminants , University Clinic for Ruminants, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna , Veterinaerplatz 1, 1210 Vienna , Austria.
authors.forename: M
authors.initials: M
authors.lastname: Iwersen
authors.affiliation: a Clinical Unit for Herd Health Management in Ruminants , University Clinic for Ruminants, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna , Veterinaerplatz 1, 1210 Vienna , Austria.
authors.forename: T
authors.initials: T
authors.lastname: Arnholdt
authors.affiliation: c First Farms A/S , 900 68 Plavecký Štvrtok , Slovakia.
authors.forename: L
authors.initials: L
authors.lastname: Meyer
authors.affiliation: a Clinical Unit for Herd Health Management in Ruminants , University Clinic for Ruminants, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine Vienna , Veterinaerplatz 1, 1210 Vienna , Austria.
authors.forename: D
authors.initials: D
authors.lastname: Klein-Jöbstl
mesh_terms: D000818:Animals; D002417:Cattle; D003126:Colostrum / Q000737:chemistry / Q000276:immunology; D003612:Dairying / Q000295:instrumentation / Q000379:methods; D005779:Immunodiffusion / Q000379:methods / Q000662:veterinary; D007074:Immunoglobulin G / Q000032:analysis; D012031:Refractometry / Q000662:veterinary; D015203:Reproducibility of Results
chemical_list: D007074:Immunoglobulin G
keywords: Colostrum quality; accuracy; brix refractometer; hydrometer; validation