Lough D S, Beede D K, Wilcox C J
Dairy Science Department, University of Florida, Gainesville 32611-0701.
J Dairy Sci. 1990 Feb;73(2):413-24. doi: 10.3168/jds.S0022-0302(90)78688-2.
Thirty-six midlactation Holstein cows were used in a randomized incomplete block design to evaluate lactational responses to varying dietary concentrations of Mg supplemented by MgO or Mg chelate. Basal diet was 41:4:55 corn silage:cottonseed hulls:concentrate (.21% total Mg). Magnesium oxide was added to the basal diet to give .32, .37, and .43% total dietary Mg, and Mg chelate was added to provide .23, .25, and .27% Mg, DM basis. Dietary treatments were formulated to supply equal concentrations of bioavailable Mg from either Mg source. Dry matter intake and milk yield were greater by cows fed MgO-supplemented than Mg chelate-supplemented treatments. Milk fat percentages were not affected. Milk protein percentages increased with Mg chelate compared with protein percentages with MgO. Treatments did not affect gross efficiency (4% FCM/DM intake) or body weight change. Lack of response to Mg chelate suggested that either the bioavailability was not as high as assumed or that sufficient total bioavailable Mg was not provided in those treatments. A companion in vitro experiment showed that MgO-supplemented concentrates, with more total supplemental Mg, supplied two to three times more soluble Mg than Mg chelate-supplemented concentrates.
选用36头泌乳中期的荷斯坦奶牛，采用随机不完全区组设计，以评估氧化镁（MgO）或镁螯合物补充不同日粮镁浓度时的泌乳反应。基础日粮为玉米青贮：棉籽壳：精料 = 41:4:55（总镁含量0.21%）。向基础日粮中添加氧化镁，使日粮总镁含量分别达到0.32%、0.37%和0.43%，添加镁螯合物，以干物质计，使日粮镁含量分别达到0.23%、0.25%和0.27%。日粮处理旨在使两种镁源提供等量的生物可利用镁。饲喂氧化镁补充日粮的奶牛干物质采食量和产奶量高于饲喂镁螯合物补充日粮的奶牛。乳脂率不受影响。与氧化镁相比，镁螯合物组乳蛋白率升高。处理对总效率（4%标准乳/干物质采食量）或体重变化无影响。对镁螯合物无反应表明，要么其生物利用率不如预期高，要么这些处理中未提供足够的总生物可利用镁。一项体外配套试验表明，总补充镁含量更高的氧化镁补充精料提供的可溶性镁比镁螯合物补充精料多两到三倍。
