Dietary Phytase and Lactic Acid-Treated CerealGrains Differently Affected Calcium and PhosphorusHomeostasis from Intestinal Uptake to SystemicMetabolism in a Pig Model

Abstract

High intestinal availability of dietary phosphorus (P) may impair calcium (Ca)homeostasis and bone integrity. In the present study, we investigated the effect of phytasesupplementation in comparison to the soaking of cereal grains in 2.5% lactic acid (LA) on intestinalCa and P absorption; intestinal, renal, and bone gene expression regarding Ca and P homeostasis;bone parameters; and serum levels of regulatory hormones in growing pigs. Thirty-two pigs wererandomly assigned to one of four diets in a 2 × 2 factorial design in four replicate batches for 19days. The diets comprised either untreated or LA-treated wheat and maize without and withphytase supplementation (500 phytase units/kg). Although both treatments improved the Pbalance, phytase and LA-treated cereals differently modulated gene expression related to intestinalabsorption, and renal and bone metabolism of Ca and P, thereby altering homeostatic regulatorymechanisms as indicated by serum Ca, P, vitamin D, and fibroblast growth factor 23 levels.Moreover, phytase increased the gene expression related to reabsorption of Ca in the kidney,whereas LA-treated cereals decreased the expression of genes for osteoclastogenesis in bones,indicating an unbalanced systemic availability of minerals. In conclusion, high intestinalavailability of dietary P may impair Ca homeostasis and bone integrity.

Keywords: bone; calcium; gene expression; growing pigs; intestine; kidney; lactic acid soaking; phosphorus; phytase.

Figure 1

Content of soluble phosphorus (% of tP) in the stomach of pigs fed either Con (), LA (), Con-Phy (), and LA-Phy () for 18 days. Values are least square means (n = 8/diet), with their SEM represented by vertical bars. Statistically significant (p < 0.05) effects of treatment are indicated by different letters (a, b, c).

Figure 2

Phosphorus and calcium balance in pigs fed either Con (), LA (), Con-Phy (), and LA-Phy (). (a) Urinary phosphorus (P) excretion (% of dietary intake); (b) urinary calcium (Ca) excretion; (% of dietary intake); (c) ratio of excreted Ca:P in urine; (d) P absorption (% of dietary intake); (e) Ca absorption (% of dietary intake); (f) ratio of absorbed Ca:P; (g) P retention (% of dietary intake); (h) Ca retention (% of dietary intake); and (i) ratio of retained Ca:P; Values are least square means (n = 8/diet), with their SEM represented by vertical bars. Statistically significant (p > 0.05) effects of treatment are indicated by different letters (a,b,c). The nutrient intake, nutrient excretion in feces and urine, as well as absorption and retention were calculated as the mean of the three days of sampling (experimental day 15 to day 17).

Figure 3

Content of calcium, phosphorus, 25(OH)D3, fibroblast growth factor 23, osteocalcin, alkaline phosphatase, and parathyroid hormone in the serum of pigs fed either Con (), LA (), Con-Phy (), and LA-Phy () for 18 days. (a) phosphorus (mmol/L); (b) calcium (mmol/L); (c) ratio of Ca:P in serum; (d) product of Ca × P in serum; (e) vitamin D (ng/mL); (f) fibroblast growth factor (pg/mL); (g) parathyroid hormone parathormon (pg/mL); (h) osteocalcin (ng/mL); (i) alkaline phosphatase (U/L). Values are means (n 8/diet), with their standard errors represented by vertical bars. Statistically significant (p < 0.05) effects of treatment are indicated by different letters (a,b,c).

Figure 3

Content of calcium, phosphorus, 25(OH)D3, fibroblast growth factor 23, osteocalcin, alkaline phosphatase, and parathyroid hormone in the serum of pigs fed either Con (), LA (), Con-Phy (), and LA-Phy () for 18 days. (a) phosphorus (mmol/L); (b) calcium (mmol/L); (c) ratio of Ca:P in serum; (d) product of Ca × P in serum; (e) vitamin D (ng/mL); (f) fibroblast growth factor (pg/mL); (g) parathyroid hormone parathormon (pg/mL); (h) osteocalcin (ng/mL); (i) alkaline phosphatase (U/L). Values are means (n 8/diet), with their standard errors represented by vertical bars. Statistically significant (p < 0.05) effects of treatment are indicated by different letters (a,b,c).