Dietary branched-chain amino acids modulate the dynamics of calcium absorption and reabsorption in proteinrestricted pigs

Background: Very low-protein(VLP) diets negatively impact calcium(Ca) metabolism and absorption. The objective of this study was to investigate the effect of supplemental branched-chain amino acids(BCAA) and limiting amino acids(LAA) on Ca digestibility, absorption and reabsorption in pigs fed with VLP diets. Forty-eight piglets were assigned to six treatments: positive control(PC), negative control(NC), and NC containing LAA 25%, LAA 50%,LAA + BCAA 25%(LB25) and LAA + BCAA 50%(LB50) more than recommendations.Results: Relative to PC or NC, LB25 and LB50 had higher digestibility of Ca and plasma Ca and phosphorus(P), but lower plasma vitamin D3. LB50 tended to increase vitamin D receptor transcript and protein in the gut, but decreased mRNA or protein abundance of parathyroid hormone 1 receptor(PTH1 R), calbindin 1(CALB1),cytochrome P450 family 27 subfamily B member 1 and occludin in small intestine. LB50 increased the transcript of cytochrome P450 family 24 subfamily A member 1 and PTH1 R but decreased the transcript of transient receptor potential cation channel subfamily V member 5, CALB1 and solute carrier family 17 member 4 in kidney.Conclusion: Overall, BCAA increased Ca digestibility through regulating the transcellular and paracellular Ca absorption in the gut and reabsorption in kidney during protein restriction.