Abstract:

[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%.

Key words: magnesium oxide, dairy cows, lactation performance, serum magnesium level, urine pH value