Digestible phosphorus needs of terminal-cross growing-finishing pigs

Growth and digestion experiments were conducted to estimate the digestible P needs of terminal-cross growing-finishing pigs fed sorghum-soybean meal-based diets from 25 to 118 kg. Dietary available P levels approximated the levels recommended by the NRC (1988) or were approximately 25% above or below those levels. Up to 80 kg, dietary treatment did not affect performance; from 80 to 118 kg, the lowest P level (no inorganic P) reduced (P = .03) feed efficiency. Carcass leanness, subjective quality scores for the loin, chemical content of lean, and sensory evaluation of cooked lean were not adversely affected by decreasing P. As dietary P decreased, connective tissue amount in the lean decreased (P = .06). Ash content (P < .01) and peak load (P < .05) of metacarpals and metatarsals decreased as dietary P decreased, but structural soundness scores in the live pig were unaffected by treatment. Apparent digestibility of P decreased (P = .08 to P < .01) as dietary P decreased in the diets. Estimated P excretions per pig decreased with decreasing dietary P up to 80 kg; during the 80-to-118-kg interval, P excretions were similar for pigs fed the two lowest P diets due to reduced feed efficiency of pigs fed the lowest P diet. Dietary digestible P contents maximizing performance and carcass merit were .21, .19, and .16% for pigs fed from 25 to 50, 50 to 80, and 80 to 118 kg, respectively. The results suggest that P excretions of terminal-cross pigs can be reduced by feeding less than current NRC recommendations for P without reducing performance, carcass merit, or structural soundness of live pigs.