Intake and digestibility of diets supplemented with or without phosphorus by feedlot Nellore bulls

The use of mineral supplements is a common practice in cattle finishing systems. The hypothesis of this study was that phosphorus supplementation in diets containing high concentrate would not improve the intake and digestibility by feedlot Nellore cattle. The study was conducted to evaluate the intake and digestibility of dry matter (DM), organic matter (OM), crude protein (CP) and neutral detergent fiber (NDF) on diets supplemented or not with phosphorus by feedlot Nellore bulls. Forty two Nellore bulls with an initial average weight of 296 ? 25 kg were used. The experiment lasted 120 days, consisting of four experimental periods of 28 days. The diets consisted of 20% of sugarcane bagasse plus 80% of concentrate, on a DM basis. Dietary treatments were: Diet 1 (control diet) consisted of bagasse (20%) + concentrate (80%), white salt without supplementary P with 2.4 g P/kg on a DM basis; Diet 2 (standard group) consisted of sugarcane bagasse (20%) + concentrate (80%), white salt and a commercial mineral supplement specific for feedlot cattle with 4.2 g P/kg on a DM basis; Diet 3 consisted of sugarcane bagasse (20%) + concentrate (80%), white salt and dicalcium phosphate with 5.0 g P/kg on DM basis. The diet 3 had the addition of 0.8% of dicalcium phosphate to achieve a P concentration similar to diet 2, but without other additives existing in the commercial mineral mix. The amount supplied was adjusted to allow daily orts of 10%. In order to assess the nutrient intakes, weekly samples were obtained from the orts of the animals. Fecal samples were taken once daily for three days of each experimental period. The variables were analyzed as a completely randomized arrangement using GLM procedure of SAS. There were no variations in the intake of DM, OM, CP and NDF of diets (P>0.05), with an average daily intake of 8.29 kg, 7.93 kg, 1.14 kg and 2.68 kg, respectively. The digestibility of CP did not vary between the treatments (P >0.05). Treatments with commercial mineral supplement and dicalcium phosphate decreased NDF (P=0.0163) and OMdigestibility(P=0.0489). Diets supplemented with phosphorus affected digestion of NDF and OM. Phosphorus levels of approximately 0.24 % in DMappears adequate.