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Abstract：
This study evaluated the effect of limestone solubility on the capacity of a novel consensus bacterial 6-phytase variant (PhyG) to improve phosphorus (P) and calcium (Ca) digestibility, retention, and utilization in low-Ca broiler diets containing no added inorganic phosphate (Pi). Male Ross 308 broilers (n = 1,152) were fed one of 16 experimental diets from 11 to 21 d of age in a randomized complete design (12 birds/cage, 6 cages/treatment). Diets comprised three positive controls (PC3, PC2, and PC1) containing 1.8, 1.2, or 0.6 g/kg MCP-P and 7.7, 7.0, or 6.2 g/kg Ca, respectively, and a negative control (NC) containing no added Pi (4.4 g/kg P; 2.8 g/kg phytate-P) and 5.5 g/kg Ca from either low or high solubility limestone (LSL or HSL, respectively, [with 42% and 97% solubility after 5 min at pH 3.0]), supplemented with 0, 250, 500, 1,000, or 2,000 FTU/kg of PhyG. Fecal samples collected on days 18 to 20 and ileal digesta collected on day 21 were analyzed for titanium dioxide, Ca, P, and phytate (IP6, inositol hexakisphosphate). Tibias (day 21) were analyzed for ash content. Data were analyzed by factorial analysis (2 limestone solubilities × 4 MCP-P levels and 2 limestone solubilities × 5 phytase dose levels) and exponential regression. Increasing dose levels of PhyG resulted in an exponential increase (P < 0.01) in the apparent ileal digestibility (AID) of P, ileal digestible P content of the diet, ileal IP6 content, and IP6 disappearance in birds fed either HSL or LSL diets, but AID Ca and ileal digestible Ca were exponentially increased by the phytase only in HSL diets (P < 0.01). Relative to HSL, the LSL increased AID P, ileal digestible P, and IP6 disappearance (P < 0.05) but reduced AID Ca, ileal digestible Ca, and retainable Ca (P < 0.05), resulting in reduced retainable P and tibia ash. Phytase exponentially increased the apparent total tract digestibility of P, retainable P, and tibia ash in HSL and LSL diets, but at or above 500 FTU/kg values were higher in HSL than LSL (interaction P < 0.05). The findings highlight that phytase dose-response effects on mineral digestibility and utilization are different for high- and low-solubility limestones, and it is therefore recommended to use digestible rather than total Ca content during diet formulation to ensure an optimal balance of Ca and P, especially in low-Ca diets. In diets containing HSL, higher phytase dose levels may be needed to compensate for the low digestible P content of the basal diet.
In broilers, an excess of dietary calcium (Ca) or imbalance with phosphorus (P) can impair mineral digestion and utilization. As a result, diets are being formulated with less Ca, but the quality of the added Ca (that is mainly from limestone) is also important. This study investigated effects of limestone solubility (high [HSL] vs. low [LSL]) on the capacity of a novel consensus bacterial 6-phytase variant, PhyG, to improve P and Ca digestion and utilization in low-Ca diets containing no added inorganic phosphate. Increasing the phytase dose increased ileal P and phytate digestibility and the digestible P content of the diet at 21 d of age regardless of limestone solubility and reduced the negative effects of HSL (relative to LSL). Total tract digestibility of P and Ca, retainable P and Ca, and tibia ash were also increased by phytase, but responses were reduced with LSL relative to HSL. The findings highlight that phytase dose-responses differ in diets containing different limestones and it is therefore recommended to formulate diets based on the content of digestible rather than total Ca to ensure that Ca requirements are met but not exceeded, with optimal phytase efficacy. In diets containing HSL, a higher PhyG dose level is needed to meet the requirement for P.
In broilers, an excess of dietary calcium (Ca) or imbalance with phosphorus (P) can impair mineral digestion and utilization. As a result, diets are being formulated with less Ca, but the quality of the added Ca (that is mainly from limestone) is also important. This study investigated effects of limestone solubility (high [HSL] vs. low [LSL]) on the capacity of a novel consensus bacterial 6-phytase variant, PhyG, to improve P and Ca digestion and utilization in low-Ca diets containing no added inorganic phosphate. Increasing the phytase dose increased ileal P and phytate digestibility and the digestible P content of the diet at 21 d of age regardless of limestone solubility and reduced the negative effects of HSL (relative to LSL). Total tract digestibility of P and Ca, retainable P and Ca, and tibia ash were also increased by phytase, but responses were reduced with LSL relative to HSL. The findings highlight that phytase dose-responses differ in diets containing different limestones and it is therefore recommended to formulate diets based on the content of digestible rather than total Ca to ensure that Ca requirements are met but not exceeded, with optimal phytase efficacy. In diets containing HSL, a higher PhyG dose level is needed to meet the requirement for P.
摘要：
这项研究评估了石灰石溶解度对新型共有细菌6-植酸酶变体（PhyG）提高磷（P）和钙（Ca）消化率的能力的影响，保留,在不添加无机磷酸盐（Pi）的低钙肉鸡日粮中的利用。雄性Ross308肉鸡（n=1,152）在随机完整设计的11至21日龄的16种实验饮食中的一种（12只鸟/笼，6个笼子/治疗）。饮食包括三个阳性对照（PC3，PC2和PC1），含有1.8，1.2或0.6g/kgMCP-P和7.7，7.0或6.2g/kgCa，分别,和阴性对照（NC），不含添加的Pi（4.4g/kgP；2.8g/kg植酸盐-P）和5.5g/kg来自低或高溶解度石灰石的Ca（LSL或HSL，分别,[在pH3.0下5分钟后溶解度分别为42%和97%])，补充0、250、500、1,000或2,000FTU/kg的PhyG。分析第18天至第20天收集的粪便样品和第21天收集的回肠消化物中的二氧化钛，Ca,P,和植酸（IP6，肌醇六磷酸）。分析Tibias(第21天)的灰分含量。通过析因分析（2个石灰石溶解度×4个MCP-P水平和2个石灰石溶解度×5个植酸酶剂量水平）和指数回归分析数据。增加PhyG的剂量水平导致P的表观回肠消化率（AID）呈指数增加（P<0.01），饮食中回肠可消化的P含量，回肠IP6含量，在喂HSL或LSL饮食的鸟类中IP6消失，但仅在HSL日粮中，植酸酶使AIDCa和回肠可消化Ca呈指数增加（P<0.01）。相对于HSL,LSL增加了AIDP，回肠可消化P，IP6消失（P<0.05），但AIDCa降低，回肠可消化Ca，和可保持的Ca（P<0.05），导致可保留的磷和胫骨灰分减少。植酸酶指数增加P的表观总道消化率，可保留的P，HSL和LSL饮食中的胫骨灰分，但在500FTU/kg或以上，HSL高于LSL（交互作用P<0.05）。研究结果表明，植酸酶对高，低溶解度石灰岩的矿物质消化率和利用的剂量反应效应是不同的，因此，建议在饮食配方过程中使用可消化的而不是总的Ca含量，以确保Ca和P的最佳平衡，尤其是低钙饮食。在含有HSL的饮食中，可能需要更高的植酸酶剂量水平来补偿基础饮食中可消化的磷含量低。
在肉鸡中，饮食中钙（Ca）的过量或磷（P）的不平衡会损害矿物质的消化和利用。因此,饮食中的钙含量较低，但是添加的Ca（主要来自石灰石）的质量也很重要。这项研究调查了石灰石溶解度的影响（高[HSL]与低[LSL])对新型共有细菌6-植酸酶变体的能力，PhyG,在不添加无机磷酸盐的低钙日粮中改善P和Ca的消化和利用。增加植酸酶剂量可增加21日龄时回肠P和植酸消化率以及饮食中可消化的P含量，而与石灰石的溶解度无关，并减少了HSL（相对于LSL）的负面影响。P和Ca的总肠道消化率，可保持的P和Ca，植酸酶也增加了胫骨灰分，但相对于HSL，LSL的反应降低。研究结果强调，植酸酶的剂量反应在含有不同石灰岩的饮食中有所不同，因此建议根据可消化而不是总Ca的含量来制定饮食，以确保满足但不超过Ca的要求。具有最佳的植酸酶功效。在含有HSL的饮食中，
在肉鸡中，饮食中钙（Ca）的过量或磷（P）的不平衡会损害矿物质的消化和利用。因此,饮食中的钙含量较低，但是添加的Ca（主要来自石灰石）的质量也很重要。这项研究调查了石灰石溶解度的影响（高[HSL]与低[LSL])对新型共有细菌6-植酸酶变体的能力，PhyG,在不添加无机磷酸盐的低钙日粮中改善P和Ca的消化和利用。增加植酸酶剂量可增加21日龄时回肠P和植酸消化率以及饮食中可消化的P含量，而与石灰石的溶解度无关，并减少了HSL（相对于LSL）的负面影响。P和Ca的总肠道消化率，可保持的P和Ca，植酸酶也增加了胫骨灰分，但相对于HSL，LSL的反应降低。研究结果强调，植酸酶的剂量反应在含有不同石灰岩的饮食中有所不同，因此建议根据可消化而不是总Ca的含量来制定饮食，以确保满足但不超过Ca的要求。具有最佳的植酸酶功效。在含有HSL的饮食中，
