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

L. S. Alexander^*,, A. Qu^*, S. A. Cutler^*, A. Mahajan^*,, S. M. Lonergan^*, M. F. Rothschild^*,, T. E. Weber, B. J. Kerr and C. H. Stahl

^* Department of Animal Science, Iowa State University, Ames, IA 50010 , Department of Animal Science, North Carolina State University, Raleigh, NC 27695 , Center for Integrative Animal Genomics, Iowa State University USDA-ARS, Ames, IA 50011

chad_stahl{at}ncsu.edu

Abstract

Concern over the environmental impact 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 following 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 % were determined. Pigs fed the PD diet had decreased (P < 0.05) plasma P concentrations and poorer G:F (P < 0.05) over the length of the trial. After 4 wk on trial, pigs fed the PD diet had increased (P < 0.05) plasma 1,25(OH)₂D₃ and decreased (P < 0.05) plasma parathyroid hormone (PTH) compared to those fed the PA diet. At the end of the trial, pigs fed the PD diet had decreased (P < 0.05) live weight, HCW, and % fat-free lean (FFL), and tended to have decreased LM area (P = 0.06) and marbling (P = 0.09) and greater (P = 0.12) 10^th-rib backfat than pigs fed the PA diet. Additionally, animals fed the PD diet had weaker bones and also decreased (P < 0.05) ash % and increased (P < 0.05) concentrations of CYP27B1 and PTHR mRNA in kidney tissue. Regardless of dietary treatment, PIC337 sired pigs consumed more feed and gained more weight than their PIC280 sired counterparts (P < 0.05) during the study. The PIC337 sired pigs also had greater (P < 0.05) HCW, larger (P < 0.01) LM area, and tended to have (P = 0.07) greater dressing percentage. Meat from the PIC337 sired pigs also tended to have greater (P = 0.12) concentrations of lactate, but decreased (P = 0.07) concentrations of total glucose units 24 h post-harvest. While plasma 1,25(OH)₂D₃ concentrations were elevated (P < 0.05) in all the animals fed the PD diet, this elevation due to P deficiency tended (P = 0.09) to be greater in the PIC337 sired pigs after 12 wk on the treatment. [REMOVED SEQ FIELD]The PIC337 sired pigs had stronger (P < 0.01) bones with greater ash % 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 x treatment interactions (P < 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.

Key Words: bone • meat quality • phosphorus • pig