The effects of different dietary crude protein level on faecal crude protein and amino acid flow and digestibility in growing pigs

This study was conducted to evaluate the effects of dietary crude protein (CP) level on faecal CP and amino acid (AA) flow and digestibility, faecal and ileal digesta microbial AA composition. Eighteen Duroc × Landrace × Yorkshire barrows (60 ± 1.43 kg) were randomly divided into 3 groups with 6 barrows in each, and fed a maize–soybean meal diet at the 10% (L-CP), 13% (M-CP) and 16% (H-CP) CP levels. The results indicated the faecal total N, CP, total AA (TAA) flow increased linearly (P < 0.05) whereas dietary CP concentration increased from 10% to 16%. The DM digestibility, CP digestibility, TAA digestibility, essential amino acid and non-essential amino acid digestibility decreased linearly (P < 0.05), whereas dietary CP concentration increased from 10% to 16%. Compared with pigs in M-CP and L-CP groups, pigs in the H-CP group had higher Asp, Cys, His, Arg flow in the faeces (P < 0.05). Compared with pigs in the L-CP group, pigs in M-CP and H-CP groups had less faecal Glu, Ala, Tyr, Pro, Val, Ile, Leu and flow (P < 0.05). Faecal microbial N and AA in the L-CP group was the highest in three groups. Pigs fed a corn–soybean meal-based diet reduced in protein concentration have lower faecal N flow