1School of Animal,Rural and Environmental Sciences,Brackenhurst Campus,Nottingham Trent University,Nottingham NG25 0QF,UK.
2Department of Molecular Biology and Genetics,Research Center Flakkebjerg, Faculty of Science of Technology,Aarhus University,DK-4200 Slagelse,Denmark.
Animal. 2017 Sep;11(9):1457-1463. doi: 10.1017/S1751731117000544. Epub 2017 Mar 20.
Around 70% of total seed phosphorus is represented by phytate which must be hydrolysed to be bioavailable in non-ruminant diets. The limited endogenous phytase activity in non-ruminant animals make it common practice to add an exogenous phytase source to most poultry and pig feeds. The mature grain phytase activity (MGPA) of cereal seeds provides a route for the seeds themselves to contribute to phytate digestion, but MGPA varies considerably between species and most varieties in current use make negligible contributions. Currently, all phytases used for feed supplementation and transgenic improvement of MGPA are derived from microbial enzymes belonging to the group of histidine acid phosphatases (HAP). Cereals contain HAP phytases, but the bulk of MGPA can be attributed to phytases belonging to a completely different group of phosphatases, the purple acid phosphatases (PAPhy). In recent years, increased MGPAs were achieved in cisgenic barley holding extra copies of barley PAPhy and in the wheat HIGHPHY mutant, where MGPA was increased to ~6200 FTU/kg. In the present study, the effect of replacing 33%, 66% and 100% of a standard wheat with HIGHPHY wheat was compared with a control diet with and without 500 FTU of supplemental phytase. Diets were compared by evaluating broiler performance, ileal Ca and P digestibility and tibia development, using nine replicate pens of four birds per diet over 3 weeks from hatch. There were no differences between treatments in any tibia or bird performance parameters, indicating the control diet did not contain sufficiently low levels of phosphorus to distinguish effect of phytase addition. However, in a comparison of the two wheats, the ileal Ca and P digestibility coefficients for the 100% HIGHPHY wheat diets are 22.9% and 35.6% higher, respectively, than for the control diet, indicating the wheat PAPhy is functional in the broiler digestive tract. Furthermore, 33% HIGHPHY replacement of conventional wheat, significantly improved Ca and P digestibility over the diet-supplemented exogenous phytase, probably due to the higher phytase activity in the HIGHPHY diet (1804 v. 1150 FTU). Full replacement by HIGHPHY gave 14.6% and 22.8% higher ileal digestibility coefficients for Ca and P, respectively, than for feed supplemented with exogenous HAP phytase at 500 FTU. This indicates that in planta wheat PAPhys has promising potential for improving P and mineral digestibility in animal feed.
约 70%的总种子磷由植酸磷组成，植酸磷必须水解才能在非反刍动物日粮中具有生物可利用性。非反刍动物内源植酸酶活性有限，因此在大多数家禽和猪饲料中添加外源植酸酶是常见做法。谷物种子的成熟谷物植酸酶活性 (MGPA) 为种子本身提供了一种参与植酸消化的途径，但不同物种之间的 MGPA 差异很大，目前使用的大多数品种几乎没有贡献。目前，用于饲料补充和转基因提高 MGPA 的所有植酸酶均来自属于组氨酸酸性磷酸酶 (HAP) 的微生物酶。谷物含有 HAP 植酸酶，但大部分 MGPA 可归因于属于完全不同的磷酸酶组，即紫色酸性磷酸酶 (PAPhy) 的植酸酶。近年来，在含有额外大麦 PAPhy 拷贝的转基因大麦 cisgenic barley 和小麦 HIGHPHY 突变体中实现了更高的 MGPA，其中 MGPA 提高到约 6200 FTU/kg。在本研究中，用 HIGHPHY 小麦替代标准小麦的 33%、66%和 100%，并与含有或不含 500 FTU 补充植酸酶的对照日粮进行比较。通过在孵化后 3 周内从每个日粮 9 个重复笼中每笼 4 只鸡评估肉鸡性能、回肠钙和磷消化率以及胫骨发育，对日粮进行比较。在任何胫骨或鸟类性能参数方面，处理之间均无差异，表明对照日粮中磷含量不足以区分植酸酶添加的效果。然而，在两种小麦的比较中，100% HIGHPHY 小麦日粮的回肠钙和磷消化率分别比对照日粮高 22.9%和 35.6%，表明小麦 PAPhy 在肉鸡消化道中具有功能。此外，33% HIGHPHY 替代常规小麦显著提高了日粮补充外源植酸酶的钙和磷消化率，可能是由于 HIGHPHY 日粮中的植酸酶活性较高（1804 v. 1150 FTU）。用 HIGHPHY 完全替代可使回肠钙和磷的消化率分别比补充外源 HAP 植酸酶 500 FTU 的日粮高 14.6%和 22.8%。这表明，在植物中，小麦 PAPhys 具有提高动物饲料中磷和矿物质消化率的巨大潜力。
