Modulation of intestinal calcium and phosphate transport in young goats fed a nitrogen- and/or calcium-reduced diet

Abstract

Feeding ruminants a reduced N diet is a common approach to reduce N output based on rumino-hepatic circulation. However, a reduction in N intake caused massive changes in Ca and inorganic phosphate (P i ) homoeostasis in goats. Although a single dietary Ca reduction stimulated intestinal Ca absorption in a calcitriol-dependent manner, a concomitant reduction of Ca and N supply led to a decrease in calcitriol, and therefore a modulation of intestinal Ca and P i absorption. The aim of this study was to examine the potential effects of dietary N or Ca reduction separately on intestinal Ca and P i transport in young goats. Animals were allocated to a control, N-reduced, Ca-reduced or combined N-and Ca-reduced diet for about 6 − 8 weeks, whereby N content was reduced by 25 % compared with recommendations. In Ussing chamber experiments, intestinal Ca flux rates significantly decreased in goats fed a reduced N diet, whereas P i flux rates were unaffected. In contrast, a dietary Ca reduction stimulated Ca flux rates and decreased P i flux rates. The combined dietary N and Ca reduction withdrew the stimulating effect of dietary Ca reduction on Ca flux rates. The expression of Ca-transporting proteins decreased with a reduced N diet too, whereas P i -transporting proteins were unaffected. In conclusion, a dietary N reduction decreased intestinal Ca transport by diminishing Ca-transporting proteins, which became clear during simultaneous N and Ca reduction. Therefore, N supply in young ruminant nutrition is of special concern for intestinal Ca transport.Key words: Flux rates of calcium and phosphate: Goats: Na + -dependent P i transporter IIb: Transient receptor potential vanilloid channel type 6: Ussing chambersFeeding ruminants a N-reduced diet is preferable for economic and environmental reasons. Dietary crude protein (CP) concentrations of 11 − 12 % were recommended to meet the requirements of growing goats (1) . A reduced dietary N supply was associated with a significant reduction in urinary N excretion (2) due to increased expression of renal urea transporters, and thus greater renal urea re-absorption (3) in goats. In addition, the urea transporting capacity of the ruminal epithelium was increased due to dietary N reduction (4) . By possessing such efficient recycling mechanisms, ruminants such as goats are able to maintain rumen microbes' N supply, and therefore a sufficient synthesis of microbial protein as the most important source for host protein, provided that energy supply to the rumen flora is also adequate for microbial protein synthesis.As monogastric species do not have the similar potential to utilise N efficiently, a low-protein diet changes metabolic pathways seriously. A reduction of dietary protein leads to changes in Ca and inorganic phosphate (P i ) homoeostasis in monogastric animals and humans, including decrease in intestinal Ca absorption, reduced urinary Ca excretion and diminished plasma calcitriol and insulin-like growth factor 1 (IGF1) concentrations (5)(6)(7)(8) .Despite the N-rec...

Modulation of growth hormone receptor-insulin-like growth factor 1 axis by dietary protein in young ruminants

“…Sample size (minimum n 7/group) was determined based on metabolic data from previous work (5) with a statistical power of 0•8 and α error of 0•05. Data are given as means with their standard errors if not stated otherwise and number of animals (n).…”

“…However, it was shown that decreased dietary protein intake caused massive changes in mineral homoeostasis and vitamin D metabolism in young goats (4,5) ; this being reflected by reduced levels of blood Ca, 1,25-dihydroxyvitamin D 3 (calcitriol) and insulin-like growth factor 1 (IGF1). Protein restriction was also shown to have an impact on Ca homoeostasis, IGF1 and vitamin D metabolism in monogastric species like humans and rats (6)(7)(8) .…”

Review: Regulation of gastrointestinal and renal transport of calcium and phosphorus in ruminants

“…In goats kept on a low Ca diet or treated with vitamin D, duodenal Ca flux rates measured in Ussing chambers were significantly increased in some (Wilkens et al, 2012b) but not in all studies (Schröder et al, 1997;Sidler-Lauff et al, 2010). Higher flux rates and a more pronounced stimulation of transcellular Ca transport by dietary Ca restriction was accompanied by an increase in RNA, and protein expression of TRPV6 could be shown for the jejunum of goats indicating that this segment is more active for overall Ca absorption (Figure 6a) (Wilkens et al, 2012b;Elfers et al, 2015). Although the efficiency of net Ca absorption from the jejunum, measured by applying the Thiry-Vella loop technique, was increased in sheep with dietary Ca restriction (Abdel-Hafeez et al, 1982), this could not be demonstrated in protein expression studies and Ussing chamber experiments (Figure 6b) (Wilkens et al, 2011).…”

“…Studies provide conflicting results on the intestinal absorption of Ca. 1,25-(OH) 2 D 3 -regulated proteins, essential for transcellular Ca absorption, have been identified in the small intestine of cattle (Yamagishi et al, 2006;Schröder et al, 2015), sheep (Schröder et al, 2001;Wilkens et al, 2009Wilkens et al, , 2011 and goats (Wilkens et al, 2012b;Elfers et al, 2015). However, Ca transport across ovine and caprine epithelia when determined in vitro in the absence of an electrochemical gradient appears to be very low compared to monogastric animals such as horses using the same methods ( Figure 5) (Wilkens et al, 2017).…”

“…Restriction of P and CP intake may occur for economic reasons or because animals are kept on deficient pastures (McGrath et al, 2012;Elfers et al, 2015). This might be especially relevant in growing or fattening animals.…”