Response to dietary phosphorus deficiency is affected by genetic background in growing pigs

Abstract

<p>Concern over the environmental effect of P excretion from pig production has led to reduced dietary P supplementation. To examine how genetics influence P utilization, 94 gilts sired by 2 genetic lines (PIC337 and PIC280) were housed individually and fed either a P-adequate diet (PA) or a 20% P-deficient diet (PD) for 14 wk. Initially and monthly, blood samples were collected and BW recorded after an overnight fast. Growth performance and plasma indicators of P status were determined monthly. At the end of the trial, carcass traits, meat quality, bone strength, and ash percentage were determined. Pigs fed the PD diet had decreased (<em>P</em> < 0.05) plasma P concentrations and poorer G:F (<em>P</em> < 0.05) over the length of the trial. After 4 wk on trial, pigs fed the PD diet had increased (<em>P</em> < 0.05) plasma 1,25(OH)₂D₃ and decreased (<em>P</em> < 0.05) plasma parathyroid hormone compared with those fed the PA diet. At the end of the trial, pigs fed the PD diet had decreased (<em>P</em> < 0.05) BW, HCW, and percentage fat-free lean and tended to have decreased LM area (<em>P</em> = 0.06) and marbling (<em>P</em>= 0.09) and greater (<em>P</em> = 0.12) 10th-rib backfat than pigs fed the PA diet. Additionally, animals fed the PD diet had weaker bones and also decreased (<em>P</em> < 0.05) ash percentage and increased (<em>P</em> < 0.05) concentrations of 1α-hydroxylase and parathyroid hormone receptor mRNA in kidney tissue. Regardless of dietary treatment, PIC337-sired pigs consumed more feed and gained more BW than their PIC280-sired counterparts (<em>P</em> < 0.05) during the study. The PIC337-sired pigs also had greater (<em>P</em> < 0.05) HCW, larger (<em>P</em> < 0.01) LM area, and tended to have (<em>P</em> = 0.07) greater dressing percentage. Meat from the PIC337-sired pigs also tended to have greater (<em>P</em> = 0.12) concentrations of lactate but decreased (<em>P</em> = 0.07) concentrations of total glucose units 24 h postslaughter. Although plasma 1,25(OH)₂D₃ concentrations were elevated (<em>P</em> < 0.05) in all the animals fed the PD diet, this elevation due to P deficiency tended (<em>P</em> = 0.09) to be greater in the PIC337-sired pigs after 12 wk on the treatment. The PIC337-sired pigs had stronger (<em>P</em> < 0.01) bones with greater ash percentage than the PIC280-sired pigs. The difference in the strength of the radii between the PIC337-sired pigs fed the PA and PD diets was greater than their PIC280-sired counterparts, which resulted in sire line × treatment interactions (<em>P</em> < 0.05). These data indicate differing mechanisms of P utilization between these genetic lines. Elucidating these mechanisms may lead to strategies to increase efficiency of growth in a more environmentally friendly manner.</p>