Influence of dietary crude protein and phosphorus levels on the utilization of crude protein and phosphorus in growing pigs

Abstract Text: A study was conducted to determine the response of total tract utilization of CP and P to different CP and P levels in growing pigs. A total of 72 growing pigs (initial BW 20.9 ± 0.8 kg) were used in a randomized completely blocked design, with 9 treatments and four 10-d experimental periods giving 8 replicates per treatment. The pigs were blocked by BW and allotted to 9 treatments with a 3 × 3 factorial arrangement consisted of 3 CP levels (5.5, 9.7, or 13.9%) and 3 apparent total tract digestible P (ATTDP) levels (0.11, 0.19, or 0.27%). The CP level and ATTDP levels were adjusted using SBM and mono-calcium phosphate (MCP), respectively. Limestone was included to maintain the Ca: ATTDP ratio across diets. There was a 5-d adjustment period followed by a 5-d total collection period. Chromic oxide and ferric oxide were used as markers to time the initiation and termination of fecal collection, respectively. The daily feed intake was adjusted to 4% of the average BW of each block, in two equal daily feeding regimen at 0730 and 1730 h. Data was analyzed using PROC MIXED of SAS (9.4) and contrasts were used to test the linear and quadratic effects of increasing levels of P within each CP level, or vice versa. Digested P (g/d) was regressed against P intake (g/d) for each CP level to determine the true total tract digestibility (TTTD) of P in MCP. Digested P (g/d) increased linearly along with the increasing level of CP (P < 0.05). The determined TTTD of P in MCP for 5.5, 9.7, and 13.9% CP diets were 80.5, 82.6, and 87.9%, respectively. There were no statistical differences among the three TTTD estimates. In the nitrogen utilization results, increasing dietary P level decreased the urine nitrogen output (P < 0.05). In conclusion, the results indicated that dietary CP deficiency may limit total tract P digestion.

Keywords: crude protein, phosphorus, total tract digestibility