Absorption of Ca and P by active transport in the small intestine is regulated by calcitriol, which is the active form of vitamin D (1,25-dihydroxycholecalciferol) and the hormones calcitonin and PTH. One-alpha-hydroxycholecalciferol (1-α-OH-D3) and 25-hydroxycholecalciferol (25-OH-D3) are vitamin D metabolites that may be added to diets for pigs. Because 1-α-OH-D3 is already hydroxylated at the 1-position, only the first hydroxylation in the liver at the 25-position is needed to convert the metabolite to calcitriol. Likewise, because the 25-OH-D3 is already hydroxylated at the 25-position, only the second hydroxylation in the kidney at the 1-position is needed if this metabolite is used. It is possible that supplementation of diets with 25-OH-D3 or 1-α-OH-D3 increases absorption and retention of Ca and P by increasing the conversion efficiency to calcitriol compared with the conversion of cholecalciferol to calcitriol. It is possible that the effects on Ca and P balance differ between 25-OH-D3 and 1-α-OH-D3, but research to test this hypothesis has not been reported.
Exogenous phytase increases the digestibility of both Ca and P in pigs and it is possible that effects of supplemental vitamin D metabolites are affected by the use of microbial phytase. Therefore, the objective of this experiment was to test the hypothesis that supplementation of 25-OH-D3 or 1-α-OH-D3 affects serum bone biomarkers, digestibility and retention of Ca and P, digestibility of gross energy (GE), and concentration of digestible energy (DE) metabolizable energy (ME) in diets without or with microbial phytase fed to late-gestation sows.
Experimental design
A total of 60 gestating sows, parity 2 to 6, were fed experimental diets from d 91 to 105 of gestation. Sows were housed individually in metabolism crates and randomly allotted to 6 diets that were formulated based on corn, soybean meal, and sugar beet pulp. Diets were formulated using a 3 × 2 factorial arrangement with 3 inclusions of supplemental vitamin D metabolite (no metabolite, supplementation with 25-OH-D3 (Hy-D®; DSM, Parsippany, NJ, USA), or supplementation with 1-α-OH-D3 (Savint; Iluma Alliance, Durham, NC, USA) and 2 inclusion levels of microbial phytase [0 or 1,000 units of phytase (Quantum Blue®; AB Vista, Marlborough, UK)]. Feed was provided daily in 2 meals and a feeding level equivalent to 1.5 × the daily maintenance ME requirement was used. Fecal and urine samples were quantitatively collected, and the apparent total tract digestibility (ATTD) and retention of Ca and P in experimental diets were calculated based on intake and fecal and urine output of Ca and P. The ATTD of GE and DE and ME in diets were also calculated.
Results
There were no interactions between use of phytase and vitamin D metabolites and no effects of use of phytase and vitamin D metabolites were observed for feed intake and urine excretion (Table 1). There was no difference in the weight of feces excreted among sows fed the 3 diets containing microbial phytase, but among sows fed diets without phytase, fecal excretion was greater (P < 0.05) from sows fed the diet with no vitamin D metabolite compared with sows fed the diet supplemented with 1-α-OH-D3 (interaction; P = 0.007). There was no difference in the ATTD of dry matter (DM) and GE among the 3 diets containing microbial phytase, but among diets without phytase, the ATTD of DM and GE was greater (P < 0.05) in diets containing 1-α-OH-D3 compared with the diet without a vitamin D metabolite (interaction; P < 0.05). If no phytase was added to diets, the DE was greater in the diet containing 1-α-OH-D3 compared with the diet without a vitamin D metabolite, but if phytase was added to the diets, no difference among diets was observed (interaction; P < 0.05). In diets without microbial phytase, the ME was greater in diets containing either one of the 2 vitamin D metabolites than in the diet without one of the metabolites, but among diets with microbial phytase, the ME in the diet containing the 1-α-OH-D3 metabolite was less than in the diet with 25-OH-D3 (interaction; P < 0.05). No effects of microbial phytase on ATTD of DM or GE, or on concentrations of DE and ME were observed.
There were no interactions between vitamin D metabolites and phytase supplementation. Regardless of metabolite supplementation, use of microbial phytase increased (P < 0.05) the ATTD of Ca and P and Ca and P retention (gram per day and percentage; Table 2). Regardless of dietary phytase, the ATTD of Ca and P was greater (P < 0.05) for sows fed a diet containing one of the vitamin D metabolites compared with sows fed a diet without a vitamin D metabolite. Calcium and P retentions (gram per day and percentage) were greater (P < 0.05) for sows fed a diet containing one of the 2 vitamin D metabolites compared with sows fed a diet without one of the metabolites.
Serum biomarkers for bone formation or bone resorption were not affected by addition of phytase or vitamin D metabolites to the diets.
Key points
- Supplementation of 1-α-OH-D3 increased digestibility of GE and concentration of ME in diets containing no microbial phytase.
- Vitamin D metabolites and microbial phytase increased digestibility and retention of Ca and P.
- Serum biomarkers were not affected by addition of phytase or vitamin D metabolites to the diets.
Table 1. Apparent total tract digestibility (ATTD) of dry matter (DM) and gross energy (GE) and concentrations of digestible energy (DE) and metabolizable energy (ME) in diets fed to sows in late-gestation1
a-cWithin a row, means without a common superscript differ (P < 0.05).
1Each least squares mean represents 10 observations except that there were only 9 observations for the 2 diets containing 25-OH-D3.
Table 2. Apparent total tract digestibility (ATTD) of Ca and P and retention of Ca and P in diets fed to sows in late-gestation1
a-bWithin a row, means without a common superscript differ (P < 0.05).
1Each least squares mean represents 10 observations except that there were only 9 observations for the 2 diets containing 25-OH-D3.