Guyton A D, McKinney J M, Knowlton K F
Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
J Dairy Sci. 2003 Dec;86(12):3972-82. doi: 10.3168/jds.S0022-0302(03)74008-9.
The effect of starch source and phytic acid (PA) supplementation on phosphorus (P) partitioning and ruminal phytase activity was evaluated in eight midlactation cows (four ruminally cannulated). Cows were randomly assigned to treatments in replicated 4 x 4 Latin squares with four 18-d periods. Diets included dry ground corn (DG) or steam-flaked corn (SF), with no supplemental P (L; 0.33% P) or supplemental purified PA (0.44% P) to provide additional P from a nonmineral source. Total collection of milk, urine, and feces was conducted on d 16 to 18 of each period. Ruminal fluid was sampled and ruminal pH measured every 8 h on d 17 and 18. Milk yield was unaffected by starch source, despite lower DMI by cows fed SF. Cows fed SF had increased DM digestibility compared with those fed DG, and tended to have higher efficiency of milk yield (1.40 vs. 1.35 kg of milk/kg of DMI). Intake and fecal excretion of P was lower in cows fed SF than in cows fed DG. In cows fed SF, milk P as a percentage of P intake increased compared with cows fed DG. Ruminal pH was unaffected by diet, but milk fat content was lower for cows fed SF. Milk yield, DMI, and feed to milk ratio were not affected by supplementation with PA. Although cows fed PA had increased P intake compared with cows fed low P diet, increased P excretion resulted in no differences in apparent P digestibility. Phosphorus balance tended to be higher in cows fed PA, but milk P as a percentage of intake was reduced. The interaction of starch source and PA affected ruminal phytase activity. Altering starch source to improve efficiency of milk yield in lactating dairy cows may help reduce P losses from dairy farms.
在八头处于泌乳中期的奶牛（四头安装了瘤胃瘘管）中评估了淀粉来源和植酸（PA）添加对磷（P）分配和瘤胃植酸酶活性的影响。奶牛被随机分配到重复的4×4拉丁方设计的处理组中，共有四个18天的周期。日粮包括干磨玉米（DG）或蒸汽压片玉米（SF），不添加额外的磷（L组，磷含量0.33%）或添加纯化的PA（磷含量0.44%）以从非矿物来源提供额外的磷。在每个周期的第16至18天收集牛奶、尿液和粪便的总量。在第17和18天，每8小时采集瘤胃液并测量瘤胃pH值。尽管饲喂SF的奶牛干物质采食量较低，但淀粉来源对牛奶产量没有影响。与饲喂DG的奶牛相比，饲喂SF的奶牛干物质消化率有所提高，且产奶效率有提高的趋势（分别为1.40和1.35千克牛奶/千克干物质采食量）。饲喂SF的奶牛的磷摄入量和粪便排泄量低于饲喂DG的奶牛。在饲喂SF的奶牛中，牛奶中的磷占磷摄入量的百分比与饲喂DG的奶牛相比有所增加。瘤胃pH值不受日粮影响，但饲喂SF的奶牛牛奶脂肪含量较低。产奶量、干物质采食量和饲料转化率不受PA添加的影响。尽管饲喂PA的奶牛与饲喂低磷日粮的奶牛相比磷摄入量增加，但磷排泄量增加导致表观磷消化率没有差异。饲喂PA的奶牛磷平衡有提高的趋势，但牛奶中的磷占摄入量的百分比降低。淀粉来源和PA的相互作用影响瘤胃植酸酶活性。改变淀粉来源以提高泌乳奶牛的产奶效率可能有助于减少奶牛场的磷损失。
