Previous studies have suggested that newborn calves should be fed shortly after birth with an adequate amount of high-quality first-milking colostrum, containing ≥ 50 mg mL–1 of colostrum IgG, to acquire transfer of passive immunity (7–9). In Germany, limited research data are available regarding the FTPI, colostrum IgG quality and influence of thermal treatments on colostrum viscosity. To our knowledge, this is the first detailed study describing the colostrum quality including color gradation, viscosity, fat and IgG concentration of first-milking postpartum dairy cattle colostrum collected randomly from healthy cows from March 2017 to February 2018. Furthermore, this study evaluated the relationship between the impact of heat treatments of colostrum and threshold of IgG on the viscosity of colostrum. In the present study, the second- and third-milking colostrum, the factors impacting the quality of colostrum such as breed, parity, season, dry period length and volume of colostrum were not included (13, 26).
Generally, physical properties of colostrum like color gradation and density or viscosity give an initial impression of the quality status of colostrum. For this study, color was assessed visually and ranged from white-pale yellow to yellow and dark-yellow, this gradation of color and degree of viscosity (watery, liquid and thick consistency) showing a significant (p ˂0.05) relationship, respectively. According to Gross et al. (27), measuring the color of cow colostrum might be a new tool to assess quality. The authors 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 concentration as well as other factors such as dietary composition being contributory factors (27–29).
In the current study, the fat content varied from 1.4 to 8.8% with a mean of 5.4% in contrast to Quigley et al. (30) who reported a higher fat content varying from 9.16 to 31.63% with a higher mean of 23.56%. On the other hand, Kehoe et al. (31) measured the colostrum fat at an average of 6.7% compared to 3.55% (32). A study on multiparous Holstein cows showed that the fat content of colostrum ranged from 2.3 to 12.5% (26). In contrast to our study, a highly variable fat content from 1.02 to 21.69% with a mean of 5.6 % on US dairy farms compared to Danish dairy farms where fat content varied from 0.6 to 14.0% with a mean of 6.02% was reported (33, 34). However, the present study showed no significant relationship between color gradation and fat content nor between various degrees of viscosity and fat contents, respectively.
Over the past two decades, various research groups have evaluated the accuracy of colostrometer (mg mL–1) and refractomter (%Brix and nD) tools either by means of comparison or with radial immunodiffusion (RID) assay used as a gold standard method. A study by Chigerwe et al. (15) compared four methods to assess the IgG concentration in dairy cows and found equal correlation coefficients of the colostrometer and Brix refractometer by comparing 0.76 and 0.75 RID values. On the other hand, Bartier et al. (12), reported that colostrometer values were highly correlated with RID values (r = 0.77) compared to RID and Brix refractometer (r = 0.64) values. Generally, these tools and the RID assay showed a strong correlation coefficient (from 0.62 to 0.87) (12, 15, 19, 30, 33–38). According to Bartier et al. (12), the reasons for variable values of correlation coefficients could be due to variations in the content of non-IgG protein in the colostrum and other factors such as dry period length, vaccination status and season of parturition that affected the concentration of dissolved components. These studies recommended both the colostrometer and refractomter as alternative, indirect, rapid and accurate on-farm tools to provide precise and reproducible results for assessing IgG concentration. Based on the previous data, we used these two indirect tools to estimate the IgG quality of German Holstein dairy cattle colostrum. Both methods showed a high degree of similarity in the classification of colostrum IgG (95%) concentration and strong correlation coefficients; 0.894 and 0.887 with %Brix and nD values, respectively, which is higher than the results reported by Bielmann et al. (35) and Quigley et al. (36) where the correlation coefficients of IgG and %Brix were relatively low (0.71 and 0.75, respectively). However, results of our study were similar to those reported by Morrill et al (37) with a correlation coefficient of 0.86. Colostrum quality in the present study revealed disparate individual IgG concentrations leading to a huge variation ranging from 4 to 116 mg mL–1 with the 58 mg mL–1 mean lower than previously reported (30) where the mean of IgG concentration was 65.8 mg mL–1. The data of the colostrometer (mg mL–1) and refractomter (%Brix and nD) in the present study revealed that 14 (37.5%), 17 (42.5%) and 14 (37.5%) samples, respectively did not show similarity to the recommended cut-point (≥ 50 mg mL–1; ≥ 20% Brix and ≥ 1.3596 nD) values. A study on Swedish dairy cows reported high variation in colostrum IgG concentrations ranging from 4 to 235 mg mL–1 with a low median of 45 mg mL–1 and the majority of cows (57.8%) produced colostrum containing IgG < 50 mg mL–1 measured by RID assay (39). However, Chigerwe et al. (15) found 32% of colostrum samples to have an inadequate IgG concentration, while Conneely et al. (40) reported that 96% of colostrum samples contained a IgG concentration >50 mg of mL–1 with a mean of 112 mg mL–1 measured by ELISA. Contrary to our study results, Morrill et al. (33) reported a higher concentration of IgG in colostrum ranging from <1 to 200 mg mL–1 with a mean of 68.8 mg mL–1 and ~30% of colostrum containing <50 mg mL–1 of IgG. On the other hand, a 72.91 mg mL–1 mean IgG concentration was determined by RID in fresh colostrum of Jersey dairy cattle ranging from 12.82 to 154.26 mg mL–1, and 32.75% of samples had <50 mg mL–1 of IgG with a mean %Brix of fresh colostrum being 21.24%, %Brix values ranging from 10.5% to 28.6% with recommended breed-specific cut points of ≥18% (37). In congruence with our %Brix value results, conventional (62.5%) and organic (56.1%) Danish dairy cattle colostrum samples had equal or exceeded cut-points of 22% Brix, with significant variation in ranging from 8.3% to 35.1% (13). A study conducted on colostrum samples of different Danish dairy cow breeds showed variation from 3 to 154 mg mL–1 of IgG concentration with an average value of 60.2 mg mL–1 (34). Elsohaby et al. (18) determined the IgG concentration of the Canadian dairy cows colostrum by RID assay ranging from 4 to 145 mg mL–1 with an average of 48 mg mL–1 and 39% of the colostrum samples showed good quality with a cut-point ≥ 50 mg mL–1. A further study by Elsohaby et al. (19) measured the colostrum IgG concentration of Canadian dairy cows that showed high values ranging from 8.4 to 232.4 mg mL–1 with a mean 64.7 mg mL–1 using RID assay and 48% of samples contained IgG lower than a cut-point of 50 mg mL–1. Determining the cut-point level for good quality colostrum by means of the Brix refractometer was previously studied (15, 35, 36, 34, 38). Our cut-point level of good quality colostrum was determined at ≥20% Brix corresponding to IgG concentration ≥50 mg mL–1 of colostrometer results. Chigerwe et al. (15) and Bielmann et al. (35) suggested 22% Brix as an optimal cut-point level compared to levels of 18%, 21% and 23% recommended for Jersey dairy cattle colostrum (12, 34, 36–38, 42).
Heat treatment of colostrum either in laboratory conditions or directly on the farm using a 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 (11, 25, 42). The present study indicates that pasteurizing colostrum at 60°C for 60 min containing ˂ 80 mg mL–1 of IgG concentration may have a minimal impact on the viscosity, whilst pasteurizing colostrum at 63.5°C for 30 min containing
˂68 mg mL–1 IgG concentration may have a moderate impact on the viscosity. Our study results correspond to the previous study where pasteurizing colostrum at 63.5°C for 30 min using a commercial batch pasteurizer produced a mildly thick coagulation consistency compared to 72°C for 15 s where heat-treatment caused a solid form of colostrum especially in samples containing
IgG > 50 mg mL–1 concentration (11). 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 compared with colostrum containing < 73.0 mg mL–1 IgG concentration (24). 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 (43). Interestingly, similar to our findings, colostrum containing > 50 mg mL–1 IgG was treated at various temperatures (57, 60 and 63°C) and times (30, 60 and 90 min) using a water bath where colostrum treated at 60°C for 30 or 60 min slightly reduced IgG concentration and did not affect viscosity (25). Donahue et al. (44) reported first-milking colostrum containing IgG between 97.4 - 36.4 mg mL–1 treated at 60°C for 60 min not showing a negative impact on IgG concentration. Nonetheless, change in the viscosity of colostrum containing IgG ≥ 80 mg mL–1 was not reported. 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 (38, 45).