Department of Animal Science, Faculty of Science and Technology, Aarhus University, AU Foulum, PO Box 50, 8830 Tjele, Denmark.
J Dairy Sci. 2013 Mar;96(3):1691-700. doi: 10.3168/jds.2011-5278. Epub 2013 Jan 9.
The effect of exogenous phytase on inositol phosphate degradation in the rumen of dairy cows was investigated in a 4 × 4 Latin square design. Four lactating Danish Holstein cows fitted with ruminal, duodenal, and ileal cannulas were offered a total mixed ration (TMR) with a high content of inositol phosphate and supplemented with 1 of 4 concentrations of phytase [none, low, medium, or high, corresponding to 23, 2,023, 3,982, and 6,015 phytase units/kg of dry matter (DM)]. Exogenous phytase lead to a higher rumen pool of phytase. Inositol phosphate content in digesta samples from rumen, duodenum, ileum, and feces was almost entirely composed of myo-inositol hexakisphosphate (InsP(6)), indicating that degradation of this compound is the rate-limiting step in inositol phosphate degradation in the digestive tract. Ruminal and total-tract degradations of InsP(6) were higher when exogenous phytase was added to the TMR. Degradation of InsP(6) occurred mainly before the duodenum. The ruminal degradability of InsP(6) was increased with increasing dietary concentrations of phytase: 86.4, 93.7, 94.5, and 96.3% for none, low, medium, or high, respectively. A comparison of the InsP(6) content in individual feedstuffs and in samples of the TMR revealed that the exogenous phytase started degrading the inositol phosphate when feeds and phytase were mixed, and thus the InsP(6) phosphorus (InsP(6)-P) content in the TMR was found to decrease with higher doses of phytase (1.69, 1.51, 1.39, and 1.25 g/kg of DM for the none, low, medium, and high phytase doses, respectively). It was not possible to distinguish between the degradation of inositol phosphate occurring in the TMR and in the rumen. Exogenous phytase had no effect on total P intake or flow of total P to the duodenum and ileum, whereas exogenous phytase increased flow of microbial P to the duodenum and total fecal P excretion. None of the investigated rumen variables (pH, degradability of neutral detergent fiber, and rumen kinetics for neutral detergent fiber) were affected by treatment. Rumen and total-tract degradations of inositol phosphate were increased when exogenous phytase was added to the TMR, which offers the potential for reducing P excretion through reduced dietary P.
在 4×4 拉丁方设计中，研究了外源性植酸酶对奶牛瘤胃肌醇磷酸盐降解的影响。4 头泌乳丹麦荷斯坦奶牛通过瘤胃、十二指肠和回肠套管接受高肌醇磷酸盐含量的全混合日粮（TMR），并补充 4 种浓度的植酸酶[无、低、中或高，分别对应于 23、2、023、3982 和 6015 植酸酶单位/千克干物质（DM）]。外源性植酸酶导致瘤胃中植酸酶的池增加。瘤胃、十二指肠、回肠和粪便中消化物样本中的肌醇磷酸盐含量几乎完全由肌醇六磷酸（InsP(6)）组成，表明该化合物的降解是肠道肌醇磷酸盐降解的限速步骤。当 TMR 添加外源性植酸酶时，InsP(6)在瘤胃和整个肠道中的降解率更高。InsP(6)的降解主要发生在十二指肠之前。随着日粮中植酸酶浓度的增加，InsP(6)的瘤胃可降解性增加：分别为无、低、中或高，分别为 86.4%、93.7%、94.5%和 96.3%。对单个饲料中 InsP(6)含量和 TMR 样品的比较表明，外源性植酸酶在饲料和植酸酶混合时开始降解肌醇磷酸盐，因此 TMR 中的 InsP(6)-P 含量随着植酸酶剂量的增加而降低（无、低、中、高植酸酶剂量分别为 1.69、1.51、1.39 和 1.25 g/kg DM）。无法区分 TMR 和瘤胃中肌醇磷酸盐的降解。外源性植酸酶对总磷摄入量或总磷向十二指肠和回肠的流量没有影响，而外源性植酸酶增加了微生物磷向十二指肠和总粪便磷排泄的流量。处理对调查的瘤胃变量（pH、中性洗涤剂纤维的可降解性和中性洗涤剂纤维的瘤胃动力学）均无影响。当 TMR 添加外源性植酸酶时，InsP(6)在瘤胃和整个肠道中的降解率增加，这为通过减少日粮磷来减少磷排泄提供了潜力。
