In this project we have studied vital physico-chemical properties and their correlation in first fresh postpartum colostrum samples collected from healthy German Holstein dairy cattle. Furthermore, this study evaluated the relationship between the impact of heat-treatment on the colostrum viscosity and threshold of IgG concentrations. Generally, physical properties of colostrum such as color gradation and visual viscosity provides an initial impression of the quality status of colostrum. In this study, a correlation between color gradation and degree of viscosity was assessed where a significant (p ˂0.05) relationship was observed. Gross et al. (17) reported that colostrum has a wide range of color spectra ranging from pale-white to dark-brown/red compared to the dairy cow milk color. The color gradation of colostrum increased progressively from pale to dark with more fat, protein and IgG as well as other factors including dietary composition also considered as contributory factors (17-19). However, a correlation between color and viscosity was not previously reported. Furthermore, the fat content varied in contrast to Quigley et al. (20) where a higher fat content (9.2 - 31.6 100 g-1; mean: 23.6 100 g-1) was reported. On the other hand, Kehoe et al. (21) measured the average colostrum fat 6.7 100 g-1 as compared to 3.6 100 g-1 (22). In contrary to the previous study (17), the present study results showed no significant relationship between color gradation and fat as well as between fat and various degrees of viscosity. This weak correlation with these parameters can possibly be due to the color variation as compared to the viscosity and fat concentration.
For assessing IgG concentration, previous studies have recommended on-farm tools to provide precise and reproducible results (6, 13, 20, 23-27). Based on these studies, we used colostrometer and refractomter as alternative indirect, rapid and accurate tools to assess the quality of German Holstein dairy cattle colostrum by estimating the IgG concentration. Both methods showed a high degree (≥95%) of similarity in the classification of colostrum IgG concentration where strong correlation coefficients (0.894 and 0.887) with %Brix and nD were observed. Interestingly, these results are higher than previously reported results (24, 26) where the correlation coefficients of IgG and %Brix were relatively low (0.71 and 0.75). However, our results were similar to Morrill et al. (27) with a correlation coefficient of 0.86. The colostrum quality, in the present study, revealed disparate individual IgG concentrations leading to a high variation but lower (69.9 mg mL-1) than the previously reported IgG concentration (20). The IgG concentration data obtained from colostrometer (mg mL-1) and refractomter (%Brix and nD), in our study, revealed that 37.5%, 42.5% and 42.5% samples did not show congurence to the recommended IgG cut-points (≥50 mg mL-1; ≥20%Brix and ≥1.3596 nD). On the other hand, 72.9 mg mL-1 IgG mean concentration was determined in Jersey dairy cattle colostrum ranging from 12.8 to 154.3 mg mL-1, and 32.8% of samples had <50 mg mL-1 IgG concentration with a mean (21.24%) %Brix of fresh colostrum, %Brix values ranging from 10.5 to 28.6% with recommended breed-specific ≥18% cut-point (27). In congruence with our %Brix results, conventional (62.5%) and organic (56.1%) Danish dairy cattle colostrum samples had equal or exceeded 22%Brix cut-point, with significant variation ranging from 8.3 to 35.1% (7). Our cut-point level of good quality colostrum was determined at ≥20%Brix corresponded to ≥50 mg mL-1 IgG concentration using colostrometer. Chigerwe et al. (13) and Bielmann et al. (25) suggested 22%Brix as an optimal cut-point level as compared to the recommended levels (18%, 21% and 23%) for Jersey dairy cattle colostrum (6, 9, 14, 24-27).
Heat-treatment of colostrum, either in experimental conditions or commercial batch pasteurization system, was previously investigated to determine the efficiency of pasteurization on viability of microorganisms to reduce calf exposure to bacterial pathogens, change in viscosity (degree of coagulation) and degradation of IgG (5, 8, 9). The present study indicates that pasteurizing colostrum at 60°C/60 min containing ≤80 mg mL-1 IgG concentration have a minimal impact on the viscosity, whilst pasteurizing colostrum at 63.5°C/30 min containing ≤68 mg mL-1 IgG concentration have a moderate impact on the viscosity. Our study results correspond to the previous study where pasteurizing colostrum at 63.5°C/30 min using a commercial batch pasteurizer produced a mildly thick coagulation viscosity compared to 72°C/15 sec where heat-treatment caused a solid form of colostrum especially in samples containing IgG concentration >50 mg mL-1 (5). Furthermore, viscosity or IgG concentration remained unaltered when colostrum was treated at 60°C for 120 min using the Rapid Visco Analyzer (RVA). However, high quality colostrum containing ≥73.0 mg mL-1 IgG concentration had a significant impact on IgG concentration and viscosity at 63°C as compared to colostrum containing <73.0 mg mL-1 IgG concentration (28). Similarly, no change in IgG concentration was observed when colostrum was treated at 60°C for 60 min using a commercial on-farm batch pasteurizer (29). Interestingly, similar to our findings, colostrum treated at various temperatures (57, 60 and 63°C) and time (30, 60 and 90 min) did not affect viscosity (8). Donahue et al. (30) reported first-milking colostrum containing IgG between 97.4 - 36.4 mg mL-1 treated at 60°C for 60 min did not show a negative impact on IgG concentration. Interestingly, change in the viscosity of colostrum containing IgG ≥80 mg mL-1 has not need reported yet. Similarly, pasteurization of first colostrum of buffaloes and cows was carried out at 63°C for 30 min, 60°C for 60 min and 72°C for 15 s where no effect on the IgG concentration and viscosity of colostrum was observed at 60°C for 60 min compared to a study where no impact on IgG concentration and quality of colostrum treated at 60°C and 63°C for 30 and 60 min was observed (13, 31). However, the cut-point of pasteurization, in our study, at different heat-treatment maintained the viscosity, IgG concentration and high quality of colostrum .