Abstract: The freezing points (FP) of raw milk from Zhongdian yak (ZY, n = 38), cattle-yak (CY, n = 85), Diqing yellow cattle (DYC, n = 18) and Simmental cattle (SC, n = 20) were measured and correlated with other physicochemical properties including somatic cell count (SCC), and urea nitrogen (UN), fat, protein and lactose contents. The results showed that the milk freezing points (MFP) of ZY, CY and DYC were ?0.589, ?0.587 and ?0.582 ℃, respectively, which were significantly lower than that of SC (?0.555 ℃). The SCC in milk from ZY, CY, DYC and SC were 52.21 × 104, 56.06 × 104, 48.67 × 104 and 45.45 × 104 cells/mL, respectively, which were not significantly different from each other (P > 0.05). Milk urea nitrogen (MUN) of ZY was 11.70 mg/100 mL, which was significantly higher than that of CY (7.63 mg/100 mL, P < 0.05) and SC (4.81 mg/100 mL, P < 0.01), and higher than that of DYC (8.51 mg/100 mL, P > 0.05). No significant correlation was observed between MFP and any other physicochemical index for ZY and DYC (P > 0.05). MFP was highly positively correlated with milk fat and SCC of CY (P < 0.01), and milk lactose and non-fat solids of SC (P < 0.01), and positively correlated with milk total solids of SC (P < 0.05). The correlation between MFP and other physicochemical indexes of all 161 milk samples tested was analyzed using Pearson correlation. The results showed that significantly positive correlations between MFP and fat, lactose or total solids content (P < 0.01), and between MFP and SCC (P < 0.05) were found. The measurement of MFP, SCC and MUN in raw milk from ZY, CY and DYC can provide an important reference for pricing of fresh raw milk based on its quality in the future.

Key words: milk, freezing point, physicochemical indexes, correlation