Available phosphorus in diets with or without ractopamine for late finishing gilts

with the objective to evaluate levels of available phosphorus (ap) in diets with or without ractopamine, 112 gilts with high genetic potential for meat deposition with initial weigh of 94.0±2.28 kg were allotted in a completely randomized block design, in a 4 × 2 factorial arrangement (0.109, 0.209, 0.309, and 0.409% ap and 0 or 5 ppm of ractopamine), with eight treatments, seven replicates, and two gilts per experimental unit. there were no interactions between ap levels and ractopamine. the levels of available phosphorus influenced both daily weight gain and daily phosphorus intake, which increased linearly. feed conversion improved in a quadratic way up to the estimated level of 0.330% ap maximum response. daily weight gain increased and feed conversion improved by adding ractopamine to the diets. serum alkaline phosphatase activity decreased linearly by increasing the levels of available phosphorus. bone strength, ash, calcium, and phosphorus contents in the bones also increased quadratically with maximum responses at 0.320, 0.270, 0.277, and 0.295% ap, respectively. the available phosphorus level of 0.330%, corresponding to a daily intake of 8.67 g of ap is suitable for 94 to 125 kg gilts selected for meat deposition fed diets with or without ractopamine.