日粮中添加不同水平氧化镁对奶牛泌乳性能、血清镁含量及尿液pH值的影响

[目的] 探究日粮中添加不同水平氧化镁对奶牛泌乳性能、血清镁含量及尿液pH值的影响。[方法] 选择胎次、泌乳量、泌乳天数相近的经产荷斯坦奶牛50头,随机分为5组,每组10头。Ⅰ组（对照组）饲喂基础日粮,Ⅱ组、Ⅲ组、Ⅳ组和Ⅴ组基础日粮中分别添加0.125%、0.250%、0.375%和0.500%的氧化镁（含量为70%）。预饲期7 d,正饲期70 d。记录采食情况和产奶量,计算干物质采食量;于试验第35天和第70天分别采集乳样、血样、尿样,测定乳蛋白含量、乳脂率、血清镁含量、尿液pH值。[结果] 在试验第35天和第70天,Ⅲ组的干物质采食量和产奶量显著（P<0.05）高于对照组;4个氧化镁添加组的乳蛋白含量均显著（P<0.05）高于对照组,Ⅲ组和Ⅳ组的乳脂率显著（P<0.05）高于对照组;4个氧化镁添加组的血清镁含量与对照组相比均无显著（P>0.05）差异;4个氧化镁添加组的尿液pH值均显著（P<0.05）高于对照组。[结论] 在奶牛日粮中添加氧化镁（含量为70%）能增加产奶量,提高乳脂率和乳蛋白含量;在该试验条件下,合理添加量为0.250%。

Effects of Dietary Supplementation of Magnesium Oxide on Lactation Performance,Serum Magnesium Level and Urine pH Value in Dairy Cows

[Objective] The aim of this experiment was to investigate the effects of dietary supplementation of magnesium oxide on lactation performance, serum magnesium level and urine pH value in dairy cows. [Method] A total of 50 multiparous Holstein dairy cows of similar parity, milk yield and day in milk were randomly assigned into 5 groups with 10 individuals in each group. The groupⅠserving as a control was fed with the basal diet, and groups Ⅱ, Ⅲ, Ⅳ and Ⅴ were fed with the basal diet supplemented with 0.125%, 0.250%, 0.375% and 0.500% of magnesium oxide powder （containing 70% magnesium oxide）, respectively. The pre-feeding trial lasted for 7 days and the formal feeding trial lasted for 70 days. The daily feed intake and milk yield of the experimental dairy cows were monitored, and the weekly dry matter intake （DMI） was calculated. The samples of fresh milk, blood and urine were collected on day 35 （5^th week） and day 70 （10^th week） of the experiment, respectively, and the milk protein content, milk fat rate, serum magnesium level and urine pH value were determined.[Result] On day 35 and day 70 of the experiment, the DMI and milk yield of group Ⅲ were significantly （P<0.05） higher than those of control; the milk protein content of the four magnesium oxide supplementation groups was all significantly （P<0.05） higher than that of control, and the milk fat rate of groups Ⅲ and Ⅳ was significantly （P<0.05） higher than that of control; there was no significant （P>0.05） difference in serum magnesium level among the four magnesium oxide supplementation groups and control, while the four magnesium oxide supplementation groups all had significantly （P<0.05） higher urine pH value in comparison to control. [Conclusion] Dietary supplementation of magnesium oxide powder （containing 70% magnesium oxide） increased the milk yield, milk fat rate and milk protein content of dairy cows; under this experimental condition, the recommended supplementation amount was 0.250%.