Hristov A N, Hazen W, Ellsworth J W
Department of Animal and Veterinary Science, University of Idaho, Moscow 83844, USA.
J Dairy Sci. 2007 Jun;90(6):3034-43. doi: 10.3168/jds.2007-0013.
Six commercial dairies from south central Idaho were surveyed to estimate the whole-farm surpluses of magnesium (Mg), sulfur (S), copper (Cu), and zinc (Zn). Mineral imports and exports were monitored in a 12-mo period and samples from the diets, feeds, feces, urine, and manure were collected at regular farm visits. Soils from manure-amended fields were sampled in the spring and fall. In all cases, the largest import of Mg, S, Cu, and Zn to the dairy was with purchased feeds, from 91 (S) to 97% (Zn) of all imports. The major mineral export item was manure [from 60% (S) to 89% (Cu) of all exports] and forages, in the case of a dairy with a large land base. Export with milk represented on average only 8.6, 25, 2.1, and 11% (Mg, S, Cu, and Zn, respectively) of all exports. Thus, the conversion of the imported feed Mg, S, Cu, and Zn into milk was rather low (on a whole-farm scale): 5.6, 11, 1.4, and 5.2%, respectively. Concentrations of Mg, Cu, and Zn in the lactating cow diets from the participating dairies exceeded National Research Council (2001) recommendations on average by 85, 34, and 73%, respectively, which contributed to the inefficient use of imported minerals. Whole-farm Mg surplus varied from 4 to 54 t/yr (3 to 19 kg/cow per year). The efficiency of use of imported Mg varied from 27 to 88%. Sulfur surpluses were from 9 to 52 t/yr (12 to 40 kg/cow per year). Copper and Zn surpluses were also significant (average of 59 and 585 kg/yr and 0.05 and 0.4 kg/cow per year, respectively). The average efficiency of use of imported S, Cu, and Mg was 44, 62, and 56%, respectively and, as with Mg, varied significantly among the dairies. The results from this study suggest that reduction in the concentration of dietary Mg, Cu, and Zn is potentially the most efficient way of reducing overall excretions and whole-farm surpluses of these minerals.
对爱达荷州中南部的6家商业奶牛场进行了调查，以估算镁（Mg）、硫（S）、铜（Cu）和锌（Zn）的全农场盈余量。在12个月的时间内监测矿物质的进出口情况，并在定期农场访问时收集日粮、饲料、粪便、尿液和粪肥的样本。对施用粪肥田地的土壤在春季和秋季进行采样。在所有情况下，奶牛场中Mg、S、Cu和Zn的最大进口来源是购买的饲料，占所有进口量的91%（S）至97%（Zn）。主要的矿物质出口项目是粪肥（占所有出口量的60%（S）至89%（Cu）），对于拥有大片土地的奶牛场来说还有草料。随牛奶出口的量平均仅占所有出口量的8.6%、25%、2.1%和11%（分别对应Mg、S、Cu和Zn）。因此，进口饲料中的Mg、S、Cu和Zn转化为牛奶的比例相当低（在全农场规模上）：分别为5.6%、11%、1.4%和5.2%。参与调查的奶牛场中泌乳奶牛日粮中的Mg、Cu和Zn浓度平均分别比美国国家研究委员会（2001年）的建议值高出85%、34%和73%，这导致进口矿物质的利用效率低下。全农场的Mg盈余量为每年4至54吨（每头奶牛每年3至19千克）。进口Mg的利用效率在27%至88%之间。S的盈余量为每年9至52吨（每头奶牛每年12至40千克）。Cu和Zn的盈余量也很显著（分别平均为每年59和585千克以及每头奶牛每年0.05和0.4千克）。进口S、Cu和Mg的平均利用效率分别为44%、62%和56%，并且与Mg一样，各奶牛场之间差异显著。本研究结果表明，降低日粮中Mg、Cu和Zn的浓度可能是减少这些矿物质总体排泄量和全农场盈余量的最有效方法。
