Optical Refractometer Research Articles

Optical frequency sweeping nonlinearity compensation implemented in a multipoint fiber optic refractometer

A multipoint fiber optic refractometer that uses an algorithm to compensate for the nonlinearity generated by an optical frequency sweeping laser is presented. This compensation allows for designing the multipoint sensing system. Otherwise, only single-point sensing is possible. Also, the nonlinearity compensation, applied to all sensing points simultaneously, permits an improvement in the resolution of each sensing point after the compensation is performed. The mathematical model and experimental results of the proposed multipoint refractive index sensor are presented.

A Comprehensive Review of Optical Fiber Refractometers: Toward a Standard Comparative Criterion

AbstractThanks to the peculiarities of optical fiber and its ability to be combined with nanotechnology, precise and accurate measurements of the changes in optical properties (i.e., refractive index) of the medium surrounding the fiber are becoming possible with a high degree of performance. Thus, optical fiber sensors (OFSs) are increasingly finding applications in biochemistry and biomedicine. Here, all types of optical fiber refractometers are covered, and they are classified into three main groups: interferometers, grating‐based structures, and resonance‐based structures (the resonance is induced by coating the optical fiber sensor with a thin film). The performance of these different structures is compared by means of the most common parameters: sensitivity, full width at half minimum or maximum, figure of merit, and quality factor. The aim here is to provide a reliable and easy‐to‐use tool to compare the performance of the most recent developments on fiber optic refractometers.

In-Fiber Closed Cavity Interferometric High-Resolution Aqueous Solution and Alcohol Gas Refractometer.

An optical fiber interferometric refractometer for alcohol gas concentration and low refractive index (RI) solution (with 1.33–1.38 RI range) measurement is theoretically and experimentally demonstrated. The refractometer is based on a single-mode thin-core single-mode (STS) interferometric structure. By embedding a suitably sized air cavity at the splicing point, high-order cladding modes are successfully excited, which makes the sensor more suitable for low RI solution measurement. The effect of the air cavity’s diameter on the sensitivity of alcohol gas concentration was analyzed experimentally, which proved that RI sensitivity will increase with an enlarged diameter of the air cavity. On this basis, the air cavity is filled with graphene in order to improve the sensitivity of the sensor; and the measured sensitivity of the alcohol gas concentration is −1206.1 pm/%. Finally, the characteristics of the single-cavity structure, graphene-filled structure and double-cavity structure sensors are demonstrated, and the linear RI sensitivities are −54.593 nm/RIU (refractive index unit), −85.561 nm/RIU and 359.77 nm/RIU, respectively. Moreover, these sensor structures have the advantages of being compact and easily prepared.

Evaluation of colostrum quality in the Czech Republic using radial immunodiffusion and different types of refractometers

The objectives of this study were to determine the immunoglobulin G concentration of colostrum in Czech dairy cows, to compare refractometer results with results achieved using the radial immunodiffusion method and to evaluate the reliability of three types of refractometers and recommend the best solution for the evaluation of colostrum quality. Colostrum samples (n = 1522) were collected from 38 herds between 2015 and 2017. The immunological quality of colostrum was estimated using Brix refractometers (optical, simple digital, digital Misco) and compared with the immunoglobulin G concentration assessed using radial immunodiffusion. We found high variability in the quality of colostrum. The minimum, maximum and median of individual measurements were the following: radial immunodiffusion immunoglobulin G – 5.2, 199.1, 76.9 g/l; optical refractometer – 9.5, 32.0, 23.1% Brix; simple digital refractometer – 5.4, 35.0, 19.1% Brix; digital refractometer Misco – 9.8, 37.4, 23.2% Brix. On the basis of immunoglobulin G concentration assessed using radial immunodiffusion, 20.9% of colostrum samples were of low quality (immunoglobulin G < 50 g/l). The Spearman correlation coefficients between radial immunodiffusion and the Brix refractometer readings were 0.62–0.67 (P < 0.001) according to the type of refractometer. The cut-off evaluation of the readings from optical and Misco digital refractometers both showed 20% Brix, with sensitivities of 89.4% and 88.2%, specificities of 73.2% and 74.5% and accuracies of 86.0% and 85.4%, respectively. The cut-off level for the simple digital refractometer showed 17% Brix with a sensitivity of 77.5%, specificity of 80.4% and an insufficient accuracy of 78.1%. For optical and Misco refractometers we recommend the use of two cut-off levels for the evaluation of colostrum: 23% Brix for the selection of good quality colostrum suitable for freezing and 19% Brix to discard poor quality colostrum. The different cut-off levels obtained by measuring with different types of refractometers indicate the need to check the quality of the instruments prior to their use in practice and, where appropriate, to determine their cut-off levels by comparison with results obtained using the reference method.

Usefulness of digital and optical refractometers for the diagnosis of failure of transfer of passive immunity in neonatal foals.

Neonatal foals with failure of transfer of passive immunity (FTPI) are at higher risk of morbidity and mortality. Successful treatment of FTPI is time-dependent, thus rapid and accurate measurement of serum IgG concentration is important for the management and care of neonatal foals. To validate the use of digital and optical refractometers for assessing FTPI in neonatal foals and compare the diagnostic performance and level of agreement of the two refractometers to the reference standard radial immunodiffusion (RID) assay. A retrospective validation study. Serum samples (n = 253) were collected from 230 foals admitted to the Veterinary Teaching Hospital and Ambulatory Equine Service between 2012 and 2017. The serum IgG concentrations were measured by the reference RID assay, digital Brix and optical refractometers. The correlation between results of two refractometers and RID assay was assessed. A receiver operating characteristic curve was created and used to identify the optimal cut-offs for evaluating sensitivity and specificity of the two refractometers to detect foals with complete and partial FTPI. The RID-IgG concentrations were positively correlated with the Brix scores obtained from a digital refractometer (r = 0.73, P = 0.001) and serum total protein obtained from an optical refractometer (r = 0.72, P = 0.001). The sensitivity and specificity of the digital Brix refractometer at optimal cut-off (≤7.8% Brix) were 88.1 (95% CI: 74.4-96.0) and 67.7% (95% CI: 60.6-74.3) to detect RID-IgG<4 g/L and 79.0 (95% CI: 68.5-87.3) and 77.3% (95% CI: 69.8-83.8) to detect RID-IgG≤8 g/L, respectively. The sensitivity and specificity of the optical refractometer at optimal cut-off (≤42 g/L) were 86.1 (95% CI: 72.1-94.7) and 70.9% (95% CI: 63.9-77.3) to detect RID-IgG<4 g/L and at cut-off (≤44 g/L) were 82.9 (95% CI: 73.0-90.3) and 72.7% (95% CI: 64.8-79.6) to detect RID-IgG≤8 g/L, respectively. The number of diseased foals was small to investigate the validity of the selected cut-off values for assessing FTPI in sick foals. The two refractometers exhibit utility as rapid, inexpensive screening tests and have a good sensitivity for assessing FTPI in neonatal foals.

Evaluation of a filter system to harvest plasma for identification of failure of passive transfer in newborn calves

The objective of this study was to evaluate a filter system to harvest plasma to assess failure of passive transfer (FPT) in newborn calves. Blood samples (n = 227) for serum and plasma harvesting were collected via jugular vein puncture from Holstein calves aged 1 to 7 d from 4 commercial dairy herds in Northeast Germany. Serum IgG concentrations were determined using a sandwich ELISA. Failure of passive transfer was defined as IgG concentrations <10 mg/mL and used as a gold standard. One handheld optical refractometer (Euromex Holland, Arnhem, the Netherlands) and 2 digital Brix refractometers (device 1: HI 96801 digital refractometer, Hanna Instruments, Woonsocket, RI; device 2: Misco PA201, Misco, Solon, OH) were used to analyze total proteins in serum or plasma. The colostrum uptake of the calf can thus be monitored and calves with FPT can be identified. Serum was obtained through centrifugation. Plasma was obtained through either a filter system or centrifugation. For plasma filtration, approximately 2 mL of lithium heparin blood was injected into the inlet reservoir of a plasma filter (2-Drop-Filter, Pharmadoc, Lübeck, Germany) using a disposable syringe. Receiver operating characteristic curve analyses were used to determine optimum thresholds for each of the 3 devices using different media. Sixty-seven (30%) calves had FPT. For the handheld optical refractometer, the optimum threshold was 5.6 g/dL [sensitivity 70.1%; specificity 80.0%; positive predictive value (PPV) 60.1%; negative predictive value (NPV) 86.2%; area under the curve (AUC) 0.85] using serum. For centrifuged plasma, the optimum threshold was 6.3 g/dL (sensitivity 82.1%; specificity 68.1%; PPV 52.5%; NPV 89.9%; AUC 0.84), and for filtered plasma, the threshold was 6.0 g/dL (sensitivity 56.7%; specificity 90.0%; PPV 70.9%; NPV 82.9%; AUC 0.80). For device 1, the optimum threshold was 8.9% Brix (sensitivity 82.1%; specificity 63.8%; PPV 48.7%; NPV 89.5%; AUC 0.81), 9.4% Brix (sensitivity 76.1%; specificity 73.7%; PPV 55.4%; NPV 87.8%; AUC 0.80), using serum and centrifuged plasma, respectively. For device 2, the optimum threshold was 8.7% Brix (sensitivity 74.6%; specificity 76.2%; PPV 57.4%; NPV 87.5%; AUC 0.83), 9.5% Brix (sensitivity 80.6%; specificity 70.6%; PPV 54.0%; NPV 89.5%; AUC 0.83), and 9.2% Brix (sensitivity 58.2%; specificity 87.5%; PPV 66.6%; NPV 83.0%; AUC 0.80) using serum, centrifuged plasma, and filtered plasma, respectively. Based on the AUC, the 3 devices yielded comparable test characteristics to identify calves with FPT. In conclusion, a filter system can be used to facilitate the evaluation of FPT as a point of care technique in calves without the need for serum centrifugation.

Using serum and plasma samples to assess failure of transfer of passive immunity in dairy calves

The objectives of this study were (1) to determine the differences in IgG and total protein (TP) content of serum and plasma samples collected from the same calves; (2) to evaluate the correlation between calf serum and plasma IgG levels, Brix scores, and TP concentrations; (3) to determine whether different cut-off values should be used for plasma and serum to assess failure of transfer of passive immunity (FTPI) in dairy calves; and (4) to evaluate the level of agreement between results obtained from using serum and plasma samples of the same calves to assess FTPI using optimal cut-off values. Blood samples (n = 217) were collected from Holstein calves at 3 to 10 d of age on 30 commercial dairy farms in Nova Scotia and Newfoundland, Canada. Paired serum and plasma samples were analyzed for IgG concentration by the reference radial immunodiffusion assay, transmission infrared (TIR) spectroscopy, digital and optical Brix refractometers, and optical TP refractometer. The IgG concentrations measured by RID and TIR spectroscopy in serum were similar to those in plasma. However, the Brix and TP refractometer readings were significantly higher in plasma than in serum. The prevalence of FTPI in serum and plasma samples based on a RID-IgG concentration <10 g/L was 43.3 and 46.5%, respectively. The RID-IgG concentration was correlated with TIR-IgG (r = 0.92 and 0.89), digital Brix (r = 0.80 and 0.80), optical Brix (r = 0.77 and 0.77), and optical TP (r = 0.75 and 0.77) refractometers in serum and plasma, respectively. The correlations between paired serum and plasma IgG content were 0.85 by TIR spectroscopy, 0.80 by digital Brix, 0.77 by optical Brix, and 0.79 by optical TP refractometer. The optimal cut-off values for TIR spectroscopy, digital Brix, optical Brix, and TP refractometers to assess FTPI using serum were 13.1 g/L, 8.7% Brix, 8.4% Brix and 5.1 g/dL, respectively; and the optimal cut-off values with plasma were 13.4 g/L, 9.4% Brix, 9.3% Brix and 5.8 g/dL, respectively. When using these optimal cut-off values, the level of agreement (88.1%) between results derived from testing serum and plasma by TIR spectroscopy was substantial, with a kappa (κ) value of 0.76. The results derived from testing serum and plasma by digital Brix refractometer showed substantial agreement (83.4%), with a κ value of 0.65, which is higher than the agreement and κ value (74.7% and 0.51) reported for the optical Brix refractometer. Substantial agreement (81.6%) between serum and plasma TP was also obtained when using the optical TP refractometer, with a κ value of 0.63. In conclusion, serum or plasma samples can be used interchangeably for measuring IgG concentrations and assessing FTPI in dairy calves. However, different cut-offs must be used to assess FTPI depending on the sample matrix. Furthermore, results obtained from serum samples showed higher agreement with the reference RID assay than those obtained from plasma samples.

Aluminum doped zinc oxide (AZO) coated optical fiber LMR refractometers—An experimental demonstration

This work presents the experimental demonstration of lossy mode resonance generation by means of aluminum doped zinc oxide thin-films. The use of such material may allow to optimize the performance of LMR-based sensors, obtaining good sensitivity at lower costs than other overlays, such as those including indium. The refractometric response of the fabricated devices is explored in different spectral regions. One refractometer working in the near infrared region was fabricated, obtaining a sensitivity of 2280 nm/RIU. A second refractometer working in the visible light spectrum was also fabricated. This second device allows to observe rough refractive index variations with the naked eye as a change of the color of the light propagating through the fiber, simplifying the setup needed for its use.

In situ measurement of seawater salinity with an optical refractometer based on total internal reflection method.

An optical refractive index sensor used for underway seawater salinity monitoring is proposed. Due to the empirical relation to salinity, refractive index measurement provides an alternative solution to obtain salinity of seawater. We developed a compact refractive index sensor based on total internal reflection (TIR) method. Through the repeatability and stability experiment and temperature correction, the performance of the sensor has been demonstrated experimentally. To evaluate the applicability of the sensor under real turbid sea conditions, field performance of the TIR sensor has been tested on an oceanographic cruise in the eastern of Yangtze Estuary in July 2017. The underway monitoring results show good correlation with the results provided by commercial CTD profiler.

Effect of Heat-treatment on Accuracy of Infrared Spectroscopy and Digital and Optical Brix Refractometers for Measuring Immunoglobulin G Concentration in Bovine Colostrum.

BackgroundHeat‐treatment of colostrum is a method developed to reduce calf exposure to pathogens. Infrared (IR) spectroscopy and Brix refractometers can be used for measuring colostral IgG concentration and assessing colostrum quality.ObjectivesTo determine the impact of heat‐treatment on accuracy of IR spectroscopy and Brix refractometers for measuring colostral IgG concentration and assessing colostrum quality before and after heat‐treatment.AnimalsA total of 60 Holstein dairy cows on 8 commercial dairy farms.MethodsA cross‐sectional study was designed to determine the effect of heat‐treatment at 60°C and 63°C each for 30 and 60 minutes duration on colostral IgG concentration measured by the reference radial immunodiffusion (RID) assay, IR spectroscopy, and digital and optical refractometers.ResultsColostrum IgG concentration significantly decreased after heat‐treatment at 63°C for 30 or 60 minutes as measured by RID, but the IgG values remained unchanged when measured by IR spectroscopy and refractometers. The lowest correlation coefficient found between IR spectroscopy (r = 0.70) and RID results was in colostrum heat‐treated at 63°C for 60 minutes. For digital (r = 0.48) and optical (r = 0.50) refractometers, the lowest correlation coefficient was at 63°C for 30 minutes when compared to RID. The accuracy of the IR spectroscopy, digital and optical Brix refractometers was decreased from 91.7 to 80%, 81.7 to 45%, and 80 to 45%, respectively, when colostrum heat‐treated at 63°C for 60 minutes.Conclusions and Clinical ImportanceRadial immunodiffusion, IR spectroscopy, and Brix refractometers exhibit utility for measuring IgG concentration when colostrum heat‐treated at 60°C but does not detect decrease IgG concentrations when heat‐treated at 63°C.

Factors affecting colostrum quality in Australian pasture‐based dairy herds

The aim of this study was to identify factors affecting colostrum quality in dairy cattle. Colostrum samples were collected from lactating dairy cows (n = 990) from nine commercial dairy herds in south-west Victoria. Colostrum quality was measured using an optical Brix refractometer. Cow-level factors thought to influence colostrum quality included season of calving, dam breed and age, volume of first-milking colostrum produced and whether the dam leaked colostrum prior to calving. Multivariable logistic regression was used to quantify the association between each cow-level factor and whether or not colostrum was assessed to be of poor quality. Cows older than 5 years of age were less likely to have poor-quality colostrum compared with primiparous heifers (odds ratio (OR) 0.62, 95% confidence interval (CI) 0.11-0.89, P = 0.009). The odds of having poor-quality colostrum was increased in cows and primiparous heifers that leaked colostrum prior to calving (OR 2.06, 95% CI, 1.33-3.17, P = 0.001). Cows and primiparous heifers that produced ≥ 8.5 L of colostrum were 1.76 times as likely to have poor-quality colostrum as individuals that produced < 8.5 L (95% CI, 1.10-2.82, P = 0.018). Visual assessment of colostrum by the herd manager was moderately correlated with colostrum quality, with 69% of poor-quality samples being correctly classified. Although this study identified factors that increase the risk of poor-quality colostrum, we concluded that objective assessment using a Brix refractometer is a more reliable means of assessing colostrum quality.

Resin Directional Flow and Degree of Cure Sensing Using Chirped Optical Fiber Long Period Gratings

The use of chirped long period gratings (CLPGs) for monitoring the flow, the direction of the flow, and the subsequent cure of an epoxy resin is presented. The asymmetric properties of the CLPG and its sensitivity to refractive index changes were exploited to facilitate the measurement of the direction of the flow. The performances of a continuously chirped LPG (CCLPG) and a step chirped LPG (SCLPG) were compared, with the CCLPG showing improved spatial resolution. The CCLPG and SCLPG were also used to monitor changes in the refractive index of the resin during cure, with the results showing close agreement with measurements undertaken simultaneously using a fiber optic Fresnel refractometer.

Design, fabrication and characterisation of silica-titania thin film coated over coupled long period fibre gratings: Towards bio-sensing applications

In this paper we report on the application of over coupled long period fibre gratings (OCLPFGs) for detecting small changes in the surrounding refractive index (SRI). In addition, the optimization of a high RI (HRI) overlay deposited over the fibre for the adhesion of biological species is described. In this study, we utilised a sol-gel-based silica-titania thin film as HRI material deposited on the grating portion using the simple and versatile dip-coating (DC) technique. The OCLPFG-based sensor has been manufactured in such a way that the resonant band retains good visibility (close to the maximum coupling condition) in the transmission spectrum even after high thermal sintering of the coating material. Three different batches of OCLPFGs were produced using different withdrawal speeds and sol viscosities. By carefully tuning both the overlay thickness during the DC process and the RI of the sol-gel material during its preparation, it was possible to bring the sensor into the so-called transition mode working region, and thus maximize the sensing performance in terms of SRI changes. All devices were characterized as optical refractometers in the RI range of interest for a bio-sensing application (from 1.33 to 1.34) and, after a suitable bio-functionalisation process, one of them was used to implement a classical receptor-analyte biosensor.

Towards a Uniform Metrological Assessment of Grating-Based Optical Fiber Sensors: From Refractometers to Biosensors.

A metrological assessment of grating-based optical fiber sensors is proposed with the aim of providing an objective evaluation of the performance of this sensor category. Attention was focused on the most common parameters, used to describe the performance of both optical refractometers and biosensors, which encompassed sensitivity, with a distinction between volume or bulk sensitivity and surface sensitivity, resolution, response time, limit of detection, specificity (or selectivity), reusability (or regenerability) and some other parameters of generic interest, such as measurement uncertainty, accuracy, precision, stability, drift, repeatability and reproducibility. Clearly, the concepts discussed here can also be applied to any resonance-based sensor, thus providing the basis for an easier and direct performance comparison of a great number of sensors published in the literature up to now. In addition, common mistakes present in the literature made for the evaluation of sensor performance are highlighted, and lastly a uniform performance assessment is discussed and provided. Finally, some design strategies will be proposed to develop a grating-based optical fiber sensing scheme with improved performance.

A true fiber optic refractometer

AbstractThe best instrument to measure the refractive index of liquids is the Abbe refractometer which can only provide accuracies of the order of 10−5 at visible wavelengths and 10−4 in the near infrared. Here we present a technique by which the exact wavelength positions in the near infrared frequency comb of a tilted grating inscribed in the core of an optical fiber can be used to measure the absolute value of the refractive index of a liquid in which the fiber is inserted, with an accuracy of ±5×10−5. This is in contrast to typical fiber optic‐based “refractometry” where only refractive index variations can be measured accurately, hence the appellation of “true” fiber optic refractometer here. In addition to the increased accuracy, the fiber refractometer proposed here offers the additional advantages associated with in situ measurements. The performance of this refractometer is demonstrated by measurements in water from room temperature down to near freezing at wavelengths in the 1550 nm window. image

Rapid assessment of bovine colostrum quality: How reliable are transmission infrared spectroscopy and digital and optical refractometers?

The objectives of this study were to evaluate the performance of the transmission infrared (IR) spectroscopic method and digital and optical Brix refractometers for measurement of colostral IgG concentration and assessment of colostrum quality of dairy cows. Colostrum samples (n = 258) were collected from Holstein cows on 30 commercial dairy farms in Nova Scotia and Newfoundland, Canada. Colostral IgG concentrations of 255 samples were measured by the reference radial immunodiffusion (RID) assay and IR spectroscopy. The Brix scores were determined on 240 of these samples using both the digital and optical Brix refractometers. Approximately half (48%) of the colostrum samples had RID IgG concentrations <50 g/L, which was the cut-point for poor quality. The correlation between RID and IR IgG concentrations was 0.88. The correlations between RID IgG concentration and Brix scores, as determined by the digital and optical refractometers, were 0.72 and 0.71, respectively. The optimal cutoff levels for distinguishing good- and poor-quality colostrum using IR spectroscopy, and digital and optical Brix refractometers were at 35 g/L and 23% Brix, respectively. The IR spectroscopy showed higher sensitivity (90%) and specificity (86%) than the digital (74 and 80%, respectively) and optical (73 and 80%, respectively) Brix refractometers for assessment of colostrum quality, as compared with RID. In conclusion, the transmission-IR spectroscopy is a rapid and accurate method for assessing colostrum quality, but is a laboratory-based method, whereas Brix refractometers were less accurate but could be used on-farm.

1470 Use of the Brix refractometer to evaluate milk replacer solutions for calves

The Brix refractometer is used on dairy farms and calf ranches for several reasons including evaluation of colostrum quality (estimation of IgG concentration), estimation of serum IgG concentration in neonatal calves, and nonsalable milk evaluation of total solids for calf nutrition. Another potential use is to estimate the total solids concentrations of milk replacer mixes as an aid in monitoring feeding consistency. The purpose of this study was to evaluate the use of Brix refractometers to estimate total solids in milk replacer solutions. Five different milk replacer powders were mixed to achieve total solids concentrations from approximately 5.5 to 18%, for a total of 90 different solutions. Both digital and optical Brix refractometers were used to compare with total solids. The two types of refractometers' readings correlated well with one another (R2 = 0.997). The Brix readings were highly correlated with the total solids percentage (R2 = 0.94). A value of approximately 1.08 to 1.47 would need to be added to the Brix reading to estimate the total solids in the milk replacer mixes. Osmolality was correlated to the Brix reading but the relationship was different depending on the type of milk replacer. The Brix refractometer can be successfully used to estimate total solids concentration in milk replacer mixes to help monitor milk replacer feeding consistency.

Design and Fabrication of Lossy Mode Resonance Based U-Shaped Fiber Optic Refractometer Utilizing Dual Sensing Phenomenon

The present work for the first time, provides a detailed analysis of U-shaped lossy mode resonance (U-LMR) fiber optic refractometer which is based on dual sensing phenomena. Theoretical and experimental studies on the sensitivities of U-LMR based fiber optic refractometer have been carried out utilizing different surrounding medium refractive indices (SRI). Also, the effect of bend diameter on the sensitivity has been investigated in detail by fabricating and analyzing zinc oxide (ZnO) coated U-shaped fiber optic probes of various bend diameters. Experimental sensitivities of the proposed U-LMR fiber optic refractometer were characterized in terms of wavelength shift, absorbance and full-width at half-maximum (FWHM) changes with respect to the SRI. With ZnO coated U-shaped fiber optic probe of bend diameter of 1.5 mm, we achieved six fold increase in the LMR sensitivity compared to the straight LMR probe. Also, in terms of the absorbance, our proposed probe was found to be four times sensitive compared to the uncoated U-shaped probe. In addition to this, for the probe diameter of 2.1 mm, sensitivity obtained by monitoring a new parameter, viz. FWHM change, is $\sim$ 900 nm/RIU which is at least 3 times better than the straight LMR probe.

Technical note: Use of a digital and an optical Brix refractometer to estimate total solids in milk replacer solutions for calves

The Brix refractometer is used on dairy farms and calf ranches for colostrum quality (estimation of IgG concentration), estimation of serum IgG concentration in neonatal calves, and nonsalable milk evaluation of total solids for calf nutrition. Another potential use is to estimate the total solids concentrations of milk replacer mixes as an aid in monitoring feeding consistency. The purpose of this study was to evaluate the use of Brix refractometers to estimate total solids in milk replacer solutions and evaluate different replacer mixes for osmolality. Five different milk replacer powders (2 milk replacers with 28% crude protein and 25% fat and 3 with 22% crude protein and 20% fat) were mixed to achieve total solids concentrations from approximately 5.5 to 18%, for a total of 90 different solutions. Readings from both digital and optical Brix refractometers were compared with total solids. The 2 types of refractometers’ readings correlated well with one another. The digital and optical Brix readings were highly correlated with the total solids percentage. A value of 1.08 to 1.47 would need to be added to the Brix reading to estimate the total solids in the milk replacer mixes with the optical and digital refractometers, respectively. Osmolality was correlated with total solids percentage of the mixes, but the relationship was different depending on the type of milk replacer. The Brix refractometer can be beneficial in estimating total solids concentration in milk replacer mixes to help monitor milk replacer feeding consistency.

Assessment of different methods to estimate bovine colostrum quality on farm

AIMS: 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 AND CLINICAL RELEVANCE: 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.