[Absence of effect of vitamin D on intestinal phytase and alkaline phosphatase: relation with phytic phosphorus in the pig].

At least two-thirds of the phosphorus ingested by pigs is in the form of phytates. Two intestinal vitamin D-sensitive enzymes, alkaline phosphatase and phytase, might be involved in phytate-P digestion. The effects of dietary vitamin D upon the two intestinal phosphatases and P utilization in pigs fed a high phytate-P diet are reported here. Fourteen vit. D-depleted pigs (25-hydroxy vit. D: about 2 ng/ml plasma) were divided into two groups fed the same basal diet containing 0.6% P (of which 80% was phytic) and 0.6% Ca. One group (+D) was supplemented for 5 weeks with vit. D (1 000 IU D3/kg diet) and the other (-D) received none. P absorption and retention was two times higher in +D pigs than in -D animals (balance technique), and tibia X-ray pictures showed a lower bone density with the -D diet than with the +D diet. Surprisingly, vit. D supplementation had no effect on either of the mucosal enzymes (phytase and alkaline phosphatase). It may be concluded that vit. D improves phytate-P absorption via a mechanism which does not involve an increase in the activity of the intestinal phosphatases.