Ex vivo intestinal studies on calcium and phosphate transport in growing goats fed a reduced nitrogen diet

In ruminant feeding, the reduction of dietary protein is an effective approach for decreasing the excretion of N. In non-ruminant species, the intestinal absorption of Ca was affected when dietary protein was reduced. Therefore, it was the aim of the present study to characterise the intestinal absorption of Ca and inorganic phosphate (P-i) in goats fed different N and Ca diets. Intestinal flux rates of Ca and P-i were determined in goats fed a reduced N and Ca diet by Ussing chamber experiments. For a more mechanistic approach, the uptake of Ca and P-i in intestinal brush-border membrane vesicles (BBMV), the expression levels of the epithelial Ca channel transient receptor potential vanilloid channel type 6 (TRPV6), the sodium-dependent P-i transporter (NaPi) IIb and the vitamin D receptor (VDR) were measured. In goats fed a reduced N and Ca diet, the intestinal flux rates of Ca and P-i were elevated. However, the reduced N and Ca diet had no effect on the uptake of Ca and P-i in intestinal BBMV, while the expression of TRPV6 and NaPi IIb protein in the corresponding intestinal segments was even decreased. The mRNA expression of NaPi IIb and VDR was not affected. Therefore, a post-transcriptional regulation of TRPV6 and NaPi IIb protein was suggested in goats fed a reduced N and Ca diet. From these data, it can be concluded that the intestinal absorption of Ca and P-i in growing goats was affected by changes in dietary N and Ca intake like those in single-stomached animals but differently modulated.