Effects of limestone particle size and dietary Ca concentration on apparent P and Ca digestibility in the presence or absence of phytase

Authors: KIM, SEON-WOO - University Of Maryland; LI, WENTING - University Of Maryland; ANGEL, ROSELINA - University Of Maryland; Proszkowiec-Weglarz, Monika

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2018
Publication Date: 7/31/2018
Citation: Kim, S., Li, W., Angel, R., Proszkowiec-Wegla, M.K. 2018. Effects of limestone particle size and dietary Ca concentration on apparent P and Ca digestibility in the presence or absence of phytase. Poultry Science. 97:4306-4314.

Interpretive Summary: Typical plant seed-based poultry diets are usually deficient in Ca and require the addition of concentrated Ca sources to meet the Ca requirement for growth. Among all the Ca sources, limestone, a naturally occurring mineral composed primarily of CaCO3, is the predominant supplement used in broiler production world-wide. However, considerable variations in limestone Ca solubility (highly correlated with particle size) and concentration have been reported even within the same country or region and preferences in limestone particle size differs among countries/regions. It is well documented that Ca has a detrimental impact on phytate-P utilization in broilers, mainly through the formation of Ca-phytate-P complexes. The present study was performed to evaluated effects of limestone particle size and Ca concentration on apparent ileal digestibility of P and Ca in the presence or absence of a 6-phytase (enzyme releasing P from phytate-P) derived from Buttiauxella sp., expressed in Trichoderma. During the experiment birds (n = 9, 3 birds/n) were fed 13 treatment diets consisting of corn-soybean meal based diet with small (PUV) and large (PAR) particle size of the limestone (mean particle size < 75 µm and =402 µm, respectively) at three Ca concentration (0.6, 0.8 and 1.0 %) and two 6-phytase levels (0 and 1000 FTU/kg). Additionally, corn-soybean meal basal diet with no inorganic Ca or 6-phytase added was fed as control diet. Starting at 27 d of age, broilers were fed the treatment diets for 32 h, then sampled for gizzard pH and distal ileal digestibility. We have shown that (1) regardless of phytase level birds fed diet with PAR limestone had similar gizzard pH in comparison to control birds (pH = 1.94), (2) gizzard pH increased in most birds fed PUV limestone diets irrespectively of phytase inclusion compared to control birds, (3) in the absence of 6-phytase, apparent P digestibility was reduced with a greater effect seen in PUV than in PAR limestone fed birds, (4) Ca apparent digestibility was lower in birds fed PUV than in those fed PAR limestone diets, and (5) apparent P ileal digestibility was not affected by increasing Ca concentration when PAR limestone was used as the Ca source, whereas apparent P ileal digestibility P decreased when PUV limestone was used as the Ca source. In summary, impact of Ca concentration on apparent digestibility of Ca and P was dependent on limestone particle size and 6-phytase inclusion. Because P digestibility was impacted by the limestone solubility, the results also suggest that particle size of the Ca source must be considered, in addition to total Ca concentration in the diet, to properly formulate the diet.

Technical Abstract: The present study evaluated effects of limestone particle size and Ca concentration on apparent ileal digestibility (AID) of P and Ca in the presence or absence of a 6-phytase derived from Buttiauxella sp., expressed in Trichoderma. Treatment diets were corn-SBM based with no added inorganic Ca or P. The design consisted of a factorial arrangement of 2 particle sizes of limestone from the same source (mean particle size: PUV < 75 µm (), PAR = 402 µm); 3 Ca (0.6, 0.8 and 1.0 %) and 2 phytase levels (0 and 1000 FTU/kg) plus the corn-SBM basal diet with no added Ca (0.14% Ca), resulting a total of 13 treatments (Trts, n = 9, 3 birds/n). Starting at 27 d of age, broilers were fed the mash diets for 32 h, then sampled for gizzard pH and distal ileal digestibility. Gizzard pH was 1.94 in birds fed diet without added Ca and was similar to those fed diet with PAR limestone regardless of phytase. Gizzard pH was increased in birds fed PUV limestone diets irrespectively of phytase inclusion compare to birds fed 0.14% Ca (P < 0.05), except in birds fed 0.60% Ca diet. In the absence of phytase, AID P was reduced as a result of increases in limestone inclusion (P < 0.05), with a greater effect seen in PUV as compared to PAR limestone. The AID Ca in birds fed PUV limestone diets was lower than that of those fed PAR limestone diets (22.1% vs. 28.2%; P < 0.05). The AID P was not affected by increasing Ca concentration when PAR limestone was used as the Ca source (average = 64.3%), whereas AID P decreased from 66.9% (0.6% Ca) to 51.0% (1.0% Ca) when PUV limestone was used as the Ca source (P < 0.05). In summary, impact of Ca concentration on AID Ca and P was dependent on limestone particle size and phytase inclusion.