ARS | Publication request: Response to Dietary Phosphate Deficiency is Affected by Genetic Background in Growing Pigs

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 12, 2008
Publication Date: October 1, 2008
Citation: Alexander, L.S., Ou, A., Cutler, S.A., Mahajan, A., Lonergan, S.M., Rothschild, M.F., Weber, T.E., Kerr, B.J., Stahl, C.H. 2008. Response to Dietary Phosphate Deficiency is Affected by Genetic Background in Growing Pigs. Journal of Animal Science. 86(10):2585-2595.

Interpretive Summary: In animals, dietary phosphorus is essential for the growth, development, and maintenance of both muscular and skeletal tissues. However, increased public and governmental concern over the environmental impact of excess phosphorus in the excreta of pigs has driven research to minimize the environmental impact of swine production. Although there is a great deal of interest in reducing phosphorus excretion by production animals, little work has examined the influence of genetics on phosphorus nutrition. Data presented indicated differing mechanisms of phosphorus utilization between two genetic lines of pigs and suggests that elucidating these mechanisms may lead to nutritional and genetic strategies to increase efficiency of phosphorus use in the pig, resulting in reduced phosphorus excretion into the environment from swine production facilities.

Technical Abstract: Concern over the environmental impact of phosphate (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 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 body weight 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 bone percent ash were determined. Regardless of sire line, pigs fed the PD diet had lower (P < 0.05) plasma P concentrations and poorer average daily gain and feed efficiency (P < 0.05) over the length of the trial. After 4 weeks on trial, PD fed pigs had increased (P < 0.05) plasma 1,25(OH)2 D3 concentrations and decreased plasma parathyroid hormone (PTH) compared to their PA fed counterparts. At the end of the trial, PD fed pigs had lower (P < 0.05) live weight, hot carcass weight, percent fat-free lean, and loin marbling, and tended to have greater (P < 0.12) 10th rib backfat than PA fed pigs. Additionally, PD fed animals also had weaker bones with lower ash percent (P < 0.05). Regardless of diet, PIC337 sired pigs consumed more feed and gained more weight than their PIC280 sired counterparts (P < 0.05). The PIC337 sired pigs also had higher (P < 0.05) hot carcass weights, larger (P < 0.05) loin muscle area, and tended to have (P < 0.07) higher percent fat-free lean. Meat from the PIC337 sired pigs also tended to have higher (P < 0.12) concentrations of lactate, but lower (P < 0.07) concentrations of total glucose units 24-h post-harvest. Whereas plasma 1,25(OH)2 D3 concentrations were elevated (P < 0.05) at 4 week in all the PD fed pigs, this increase was larger among the PIC337 sired pigs. Among the PA fed pigs, PIC337 sired pigs had the stronger bones with higher ash percent (P < 0.05). Increased (P < 0.05) concentrations of the 1-alpha hydroxylase (CYP27B1) and PTH receptor mRNA in kidney tissue were seen in PD pigs. 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.