中文摘要：

测定中甸牦牛（n＝38）、犏牛（n＝85）、迪庆黄牛（n＝18）和西门塔尔牛（n＝20）原乳的冰点、体细胞数、尿素氮以及脂肪、蛋白、乳糖含量等理化指标，并分析冰点与其他理化指标的相关性。结果表明：中甸牦牛、犏牛和迪庆黄牛乳的冰点分别为－0.589、－0.587℃和－0.582℃，极显著低于西门塔尔牛的－0.555℃（P＜0.01）；中甸牦牛、犏牛、迪庆黄牛和西门塔尔牛的乳中体细胞数分别为52.21×104、56.06×104、48.67×104个/mL和45.45×104个/mL，相互间比较差异不显著（P＞0.05）；中甸牦牛的乳尿素氮含量为11.70mg/100mL，显著高于犏牛的7.63mg/100mL（P＜0.05），极显著高于西门塔尔牛的4.81mg/100mL（P＜0.01），高于迪庆黄牛的8.51mg/100mL，但差异不显著（P＞0.05）。Pearson相关分析结果表明：中甸牦牛和迪庆黄牛乳的冰点与其他理化指标间无明显的相关性（P＞0.05），犏牛乳的冰点与乳脂肪含量、乳脂蛋白比和体细胞数呈极显著正相关（P＜0.01），西门塔尔牛乳的冰点与乳糖和乳非脂固形物含量呈极显著正相关（P＜0.01），与乳总固形物呈显著正相关（P＜0.05）；对全部乳样（n＝161）测定数据相关性分析结果，冰点与乳脂肪、乳蛋白、乳总固形物含量和乳脂蛋白比均呈极显著正相关（P＜0.01），与体细胞数呈显著正相关（P＜0.05）。本研究完成对中甸牦牛、犏牛和迪庆黄牛原乳的冰点、体细胞数、尿素氮的测定，可为今后制定生鲜乳收购按质论价标准提供参考。

英文摘要：

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,?0.587and?0.582℃,respectively,which were significantly lower than that of SC(?0.555℃).The SCC in milk from ZY,CY,DYC and SC were52.21×104,56.06×104,48.67×104and45.45×104cells/mL,respectively,which were not significantly different from each other(P>0.05).Milk urea nitrogen(MUN)of ZY was11.70mg/100mL,which was significantly higher than that of CY(7.63mg/100mL,P<0.05)and SC(4.81mg/100mL,P<0.01),and higher than that of DYC(8.51mg/100mL,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 all161milk 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.