Physiological and Transcriptional Responses in Weaned Piglets Fed Diets with Varying Phosphorus and Calcium Levels

Abstract

Phosphorus (P) is an important element of various metabolic and signalling processes, including bone metabolism and immune function. To elucidate the routes of P homeostasis and utilization, a five-week feeding study was conducted with weaned piglets receiving a diet with recommended amounts of P and Ca (M), or a diet with lower (L) or higher (H) P values and a constant Ca:P ratio. Routes of P utilization were deduced via bone characteristics (MicroCT), genome-wide transcriptomic profiles of peripheral blood mononuclear cells (PBMCs), and serum mineral levels. MicroCT revealed significantly lower bone mineral density, trabecular number, and mechanical fracture load in (L). Gene expression analyses showed transcripts of 276 and 115 annotated genes with higher or lower abundance in (H) than (L) that were related to basic cellular and metabolic processes as well as response to stimuli, developmental processes and immune system processes. This study shows the many molecular routes involved in P homeostasis that should be considered to improve endogenous mechanisms of P utilization.

Keywords: calcium homeostasis; dietary mineral intake; immunomodulation; phosphorus homeostasis; trabecular bone.

Figure 1

Representative images obtained from micro-CT analyses of porcine femurs. (A). The volume of interest (VOI) was set distal to the hip joint at 30% of the total femur length (yellow line) and covered 800 slices (light blue lines). (B). Region of interest (ROI) (red) represents the trabecular bone for measurements of bone mineral density (BMD). (C). ROI (red) to approximate the tissue mineral density (TMD) in cortical bone.

Figure 2

Daily weight gain and feed intake of piglets fed variable dietary amounts of P and Ca. Data refer to the weekly means of body weight gain and feed intake throughout the feeding trial (details are displayed in Table S2). Low P diet (white bars); Medium (recommended) P diet (gray bars); High P diet (black bars); * p < 0.05.

Figure 3

Serum inorganic P, Ca, Zn, and Cu levels of pigs fed variable dietary amounts of P and Ca. Values for serum inorganic P and Ca were obtained previously [17]. L—Low P diet; M—Medium (recommended) P diet; H—High P diet; * p < 0.05.

Figure 4

Gene Ontology (GO)-terms. Results refer to genes differentially expressed in animals fed the L and H diets. The analysis shows significantly enriched terms for (A) molecular functions and (B) biological processes.