Influence of preservation methods on the quality of colostrum sourced from New Zealand dairy farms

AIMS: To assess the effect of two temperatures (ambient temperature and 4°C), three preservation methods (no preservative, yoghurt and potassium sorbate), and two periods of storage (3 and 7 days) on Brix and total bacterial and coliform counts of colostrum collected from New Zealand dairy farms. METHODS: One litre of colostrum destined to be fed to newborn calves was collected from 55 New Zealand dairy farms in the spring of 2015. Six aliquots of 150 mL were obtained from each colostrum sample, with two aliquots left untreated, two treated with potassium sorbate and two with yoghurt, and one of each pair of aliquots stored at ambient temperature and the other at 4°C. All samples were tested for Brix, total bacterial counts and coliform counts before treatment (Day 0), and after 3 and 7 days of storage. The effect of preservation method and storage temperature on the change in Brix, bacterial and coliform counts after 3 or 7 days of storage was analysed using multivariable random effects models. RESULTS: For all outcome variables there was a temperature by preservation interaction. For aliquots preserved with potassium sorbate, changes in Brix and bacterial counts did not differ between aliquots stored at ambient temperature or 4°C, but for aliquots preserved with yoghurt or no preservative the decrease in Brix and increase in bacterial counts was greater for aliquots stored at ambient temperature than 4°C (p<0.001). For aliquots preserved with potassium sorbate, coliform counts decreased at both temperatures, but for aliquots preserved with yoghurt or no preservative coliform counts increased for aliquots stored at 4°C, but generally decreased at ambient temperatures (p<0.001). There was also an interaction between duration of storage and temperature for bacterial counts (p<0.001). The difference in the increase in bacterial counts between aliquots stored at 4°C and ambient temperature after 3 days was greater than between aliquots stored at 4°C and ambient temperature after 7 days. CONCLUSIONS AND CLINICAL RELEVANCE: Use of potassium sorbate to preserve colostrum for 3 or 7 days resulted in little or no reduction in Brix and a lower increase in total bacterial counts than colostrum stored without preservative or with yoghurt added. Colostrum quality was not affected by storage temperature for samples preserved with potassium sorbate, but storage at 4°C resulted in better quality colostrum than storage at ambient temperatures for colostrum with no preservative or yoghurt added

Comparison of diagnostic tests for determining the prevalence of failure of passive transfer in New Zealand dairy calves

AIM: To evaluate the level of agreement of three indirect testing methods with concentrations of IgG in serum, and to determine their test characteristics for diagnosing failure of passive transfer (FPT), in dairy calves in New Zealand. METHODS: From 17 July to 30 November 2015, 471 blood samples were collected from dairy calves aged 0–8 days, from 19 different commercial dairy farms in the Waikato region of New Zealand. All serum samples were tested for concentrations of IgG and total protein (TP), and gamma-glutamyl transferase (GGT) activity, and 138 samples were tested using a digital Brix refractometer. The diagnostic tests were assessed for level of agreement with concentrations of IgG using Bland-Altman plots. FPT was defined as concentration of IgG ≤10.0 g/L and receiver operating characteristic curve analysis was used to determine optimal cut-points for correctly predicting FPT. The test characteristics for TP, GGT and Brix for predicting FPT were determined using the optimal cut-points. The effect of age on the relationship between test results and concentrations of IgG was also assessed. RESULTS: Based on the limits of agreement plots, the agreement with concentrations of IgG was greatest for concentrations of TP, followed by Brix, with the lowest being GGT activity. There was an interaction between age at sampling and the association between concentrations of IgG and GGT activity (p<0.001); in calves 5–8 days of age there was a greater increase in concentrations of IgG associated with a unit increase in GGT activity than in calves <5 days of age. The optimal cut-points for diagnosis of FPT were 52 g/L for concentrations of TP, 8.8% for Brix, 250 IU/L for GGT activity in calves <5 days old, and 210 IU/L for GGT activity in calves 5–8 days old. Accuracy for predicting FPT was greatest for TP (0.95), followed by GGT in calves <5 days old (0.94) and Brix (0.92). Specificities were high for all three tests, however sensitivity varied greatly. CONCLUSION: Measurement of concentrations of TP in serum was the most accurate alternative to measuring concentrations of IgG for diagnosing FPT in non-dehydrated calves. CLINICAL RELEVANCE: Veterinary practitioners in New Zealand now have confidence in using a test that is more accurate and practical than GGT and considerably cheaper than IgG to screen for FPT