The objective of this study was to evaluate effects of dietary crude protein (CP) intake on ileal amino acid digestibilities and expression of genes for digestive enzymes in growing and finishing pigs. In Experiment 1, 18 growing pigs (average initial BW = 36.5 kg) were assigned randomly into one of three treatments (n = 6/treatment group) representing normal (18 % CP), low (15 % CP), and very low (12 % CP) protein intake. In Experiment 2, 18 finishing pigs (average initial BW = 62.3 kg) were allotted randomly into one of three treatments (n = 6/treatment group), representing normal (16 % CP), low (13 % CP) and very low (10 % CP) protein intake. In both experiments, diets with low and very low CP were supplemented with crystalline amino acids to achieve equal content of standardized ileal digestible Lys, Met, Thr, and Trp, and were provided to pigs ad libitum. Daily feed intake, BW, and feed/gain ratios were determined. At the end of each experiment, all pigs were slaughtered to collect pancreas, small-intestine samples, and terminal ileal chymes. Samples were used for determining expression of genes for digestive enzymes and ileal amino acid digestibilities. Growing pigs fed the 12 % CP and 15 % CP diets had lower final body weight (P < 0.01) and ADG (P < 0.0001) when compared with pigs fed the 18 % dietary CP diet. Growing pigs fed with the 12 % CP diet showed higher digestibilities for CP (P < 0.05), DM (P < 0.05), Lys (P < 0.0001), Met (P < 0.01), Cys (P < 0.01), Thr (P < 0.01), Trp (P < 0.05), Val (P < 0.05), Phe (P < 0.05), Ala (P < 0.05), Cys (P < 0.01), and Gly (P < 0.05) than those fed the 18 % CP diet. Finishing pigs fed the 16 % CP diet had a higher (P < 0.01) final body weight than those fed the 10 % CP diet. mRNA levels for digestive enzymes (trypsinogen, chymotrypsin B, and dipeptidases-II and III) differed among the three groups of pigs (P < 0.05), and no difference was noted in the genes expression between control group and lower CP group. These results indicated that a reduction of dietary CP by a six-percentage value limited the growth performance of growing-finishing pigs and that a low-protein diet supplemented with deficient amino acids could reduce the excretion of nitrogen into the environment without affecting weight gain.

In various pathological conditions of tissue injury, oxidative stress is often associated with autophagy.However, H 2 O 2 -induced oxidative stress initiates autophagy and its molecular mechanism is still obscure. Here we report that intragastric and peritoneal administration of H 2 O 2 caused different degrees of oxidative stress and changed intestinal permeability, morphology, and barrier function in piglets. Western blotting studies revealed that H 2 O 2 increased the autophagosome-related protein LC3-I and LC3-II abundance and the ratio of LC3-II to LC3-I content after exposure to 10% H 2 O 2 in the jejunum.Meanwhile, the data from beclin1 also indicated that H 2 O 2 initiated autophagy in response to oxidative stress. In addition, H 2 O 2 activates the NF-kB and Nrf2/Keap1 signals, which may be involved in H 2 O 2induced autophagy. In conclusion, administration of H 2 O 2 caused intestinal oxidative stress and triggered an autophagic response, which might be associated with NF-kB and Nrf2/Keap1 signals.