Effect of Phosphorus Levels on Growth Performance, Bone, and Carcass Characteristics in PIC 800-sired Nursery and Finishing Pigs

Phosphorus is involved in numerous important physiological roles, such as skeletal development, growth, and protein deposition. Previous experiments have determined the standardized total tract digestible P (STTD P) requirement for PIC 337 sired pigs, but further research is needed to evaluate the response in PIC 800 sired pigs and to validate current PIC recommendations. Therefore, a total of 1,040 pigs (initially 10.2 ± 0.19 kg) were used in a 136-d study to evaluate the effects of increasing STTD P on growth performance, bone, and carcass characteristics of PIC 800-sired, late nursery and finishing pigs. Pens of pigs were blocked by average p and allotted to one of five dietary treatments within a randomized complete block design with 26 mixed-sex pigs per pen and eight pens per treatment. Diets were corn-soybean meal-based. Three treatment diets were manufactured (low, intermediate and high P) and blended to reach the STTD P levels of 82, 89, 96, 103, and 110% of PIC recommendations for PIC 800-sired pigs. Experimental diets were provided across five feeding phases based on time: from d 0 to 18, 18 to 44, 44 to 71, 71 to 97, and 97 to 136. The PIC STTD P:NE recommendations for mixed-sex PIC-800 sired pigs for the corresponding phases are 1.75, 1.54, 1.30, 1.10, and 0.97 g/Mcal, respectively. At the third marketing event, two medium body weight pigs per pen, one gilt and one barrow within each pen were selected for bone analysis. The third metacarpal bone of the left foot was dissected and defatted to determine the percentage of ash relative to dry bone weight. A marginal improvement (linear, P = 0.087) was observed for final BW as STTD P increased. Similarly, overall (d 0 to 136) ADG increased (linear, P = 0.020) with increasing dietary STTD P, with the greatest response as STTD P increased to 103% of PIC 800 recommendations. A marginal improvement (quadratic, P < 0.099) in overall G:F was observed, with 96% of PIC 800 STTD P recommendations having the greatest G:F. No differences were observed for percentage bone ash, carcass yield, backfat or loin depth or lean percentage with increasing STTD P. Overall, hot carcass weight (HCW) marginally increased (linear, P = 0.093) through 103% in response to increasing STTD P. In conclusion, the STTD P recommendations for PIC 800 sired pigs are reasonably accurate to optimize performance. Dose response models predicted 101% of STTD P recommendations were sufficient to maximize ADG of PIC-800 grow-finishing pigs, while 97% of STTD P recommendations was sufficient for G:F.