Effects of dietary crude protein level and N-carbamylglutamate supplementation on nutrient digestibility and digestive enzyme activity of jejunum in growing pigs.

Three experiments were conducted to investigate the effects of dietary CP level and N-carbamylglutamate (NCG) supplementation on apparent total tract digestibility (ATTD) and ileal digestibility of nutrients and digestive enzyme activity of jejunum in growing pigs. In Exp. 1, ten Duroc x Landrace x Yorkshire barrows (initial BW: 48.7 kg) were allotted to a 3-period switchback design with 5 experimental diets and 2 replicate pigs per diet in each period. Diets were high-CP (HP, 18% CP), moderate low-CP (MLP, 15% CP), very low-CP (VLP, 12% CP), and MLP and VLP with 0.1% NCG supplementation. Feces and urine were collected from d 6 to 11 after a 5-d adaptation period. The DE, ME and ATTD of GE, OM, CP, NDF, ADF and P decreased (P < 0.01) with reduction of dietary CP, but no effect of dietary treatments on pig daily N retention was detected. The NCG supplementation increased (P < 0.01) DE and ATTD of ADF of VLP diet. In Exp. 2, ten jejunal-cannulated Duroc x Landrace x Yorkshire barrows (initial BW: 44.5 kg) were fed 5 diets for 3 periods as Exp. 1. Jejunal fluid was collected on d 6 and 8 after a 5-d adaptation period. The digestive enzymes activity were not affected by dietary CP level, except for alpha-amylase, for which there was a decrease (P < 0.01) in pigs fed VLP diets compared to HP and MLP diets. In Exp. 3, twelve ileal-cannulated Duroc x Landrace x Yorkshire barrows (initial BW: 46.7 kg) were allotted to a 3-period switchback design with 6 diets and 2 replicate pigs per diet in each period. The 6 experimental diets consisted of 5 experimental diets as Exp. 1 and 1 N-free diet. Ileal digesta was collected from d 6 to 8 after a 5-d adaptation period. Results indicated that apparent ileal digestibility (AID) of CP and P and ileal digestibility of Arg, His, Ile, Leu, Phe and all dispensable AA, except Pro decreased (P < 0.01) in pigs fed VLP diet compared to HP and MLP diets, but AID of GE, OM, EE, NDF, and ADF were not affected. The supplementation of NCG in VLP diet increased (P < 0.01) the AID of CP and ileal digestibility of Arg, His, Leu, Phe, Val, Ser and Tyr. In conclusion, reducing dietary CP level decreased nutrient digestibility, but improved the efficiency of dietary N utilization and reduced N emission. Moderate reduction of dietary CP level had a minimal effect on nutrient digestibility and digestive enzyme activity. Additionally, NCG supplementation plays beneficial effect on nutrient digestion only if the dietary CP level is extremely lowered.