The impact of dietary phosphorus regimen on muscle growth and quality in pig differing in lean growth capacity
An experiment was conducted to examine the impact of dietary phosphorus regimen on body tissue deposition, the efficiency of utilization of dietary available phosphorus for protein deposition, and on post-mortem exudative losses, water holding capacity and color scores during retail storage of longissimus muscle sections from pigs of two genetic strains differing in lean growth capacity. Seven sets of six littermate barrows from each of a high and moderate lean growth (LG) genotype were allotted within each litter to one of six diets differing in dietary available phosphorus (AP) concentration (.080,.110,.155,.222,.323, and.475%). Pigs were allowed to consume their experimental diets ad-libitum. At 109 ± 4 kg pigs were removed from feed at 7:00 am, transported 5 km, electrically stunned and killed by exsanguination.25 to 1.5 hr post-transport. From 20 to 109 kg, high LG pigs accrued more muscle daily, gained more weight per unit of feed, and produced carcasses with more dissectable muscle and less fatty tissue than moderate LG pigs. Longissimus muscle (LM) sections from high LG pigs had lower pH 45 minutes post-mortem, larger initial weights, higher exudative losses from d 0 to d 3, lower water holding capacities (WHC), more moisture and less fat, and were lighter in color on d 0, whereas redness and yellowness of the LM sections were unaffected by LG genotype. Longissimus muscle sections from high LG pigs had higher exudative loss early in the storage period and lower exudative loss later than LM sections from moderate LG pigs in both the fresh and post-thaw state. Longissimus muscle sections became lighter and less red in color as storage progressed; however the pattern of color change as storage progressed differed between genotypes in both the fresh and post-thaw states. As dietary AP concentration decreased, the rate of deposition of high protein, high phosphorus containing tissues (muscle, bone) decreased, whereas that of low protein, low phosphorus containing tissues (fatty tissue) increased. Pigs deposited 12 to 15 g of protein per g of dietary AP. Dietary AP concentration had minimal impact on LM quality traits. Thus, the phosphorus needs of pigs are determined largely by the animals' deposition rates of proteinaceous tissues especially those rich in phosophorus.