Abstract: The effects of crude protein (CP) levels in the diet on the mRNA expression of amino acid (AA) transporters were studied in a 45-d trial. Eighteen piglets with an initial body weight (BW) of 9.57 kg were assigned to three groups (14%, 17%, and 20% CP in the diet) in a completely randomized design (six replicates per treatment). Diets were supplemented with crystalline AA to achieve equal standardized ileal digestible contents of Lys, Met plus Cys, Thr, and Trp, and were provided ad libitum. After 45 d, all piglets were slaughtered to collect small intestine samples. Compared with the values in the 14% CP group, the expressions of ASCT2, 4F2hc, and ATB⁰ mRNA in the jejunum were increased by 23.00%, 12.00%, 6.00% and 48.00%, 47.00%, 56.00% in the 17% and 20% CP groups, respectively. These results indicate that a 14% CP diet supplemented with crystalline AA may not transport enough AA into the body and maintain growth performance of piglets. However, a reduction of dietary 17% CP may reduce the excretion of nitrogen into the environment while supporting the development of piglets. Therefore, the 17% CP level is more suitable than 14% CP level.

降低日粮粗蛋白水平对断奶仔猪营养感受体基因（氨基酸转运载体）表达的影响

[1]Abdulhussein, A.A., Wallace, H.M., 2014. Polyamines and membrane transporters. Amino Acids, 46(3):655-660.

[2]Acciaioli, A., Sirtori, F., Pianaccioli, L., et al., 2011. Comparison of total tract digestibility and nitrogen balance between Cinta Senese and Large White pigs fed on different levels of dietary crude protein. Anim. Feed Sci. Tech., 169(1-2):134-139.

[3]Chen, G., Zhang, J., Zhang, Y.Z., et al., 2014. Oral MSG administration alters hepatic expression of genes for lipid and nitrogen metabolism in suckling piglets. Amino Acids, 46(1):245-250.

[4]Deng, D., Li, A.K., Chu, W.Y., et al., 2007a. Growth performance and metabolic responses in barrows fed low-protein diets supplemented with essential amino acids. Livest. Sci., 109(1-3):224-227.

[5]Deng, D., Huang, R.L., Li, T.J., et al., 2007b. Nitrogen balance in barrows fed low-protein diets supplemented with essential amino acids. Livest. Sci., 109(1-3):220-223.

[6]Deng, D., Yao, K., Chu, W.Y., et al., 2009. Impaired translation initiation activation and reduced protein synthesis in weaned piglets fed a low-protein diet. J. Nutr. Biochem., 20(7):544-552.

[7]Fairbrother, J.M., Nadeau, E., Gyles, C.L., 2005. Escherichia coli in postweaning diarrhea in pigs: an update on bacterial types, pathogenesis, and prevention strategies. Anim. Health Res. Rev., 6(1):17-39.

[8]Franklin, M.A., Mathew, A.G., Vickers, J.R., et al., 2002. Characterization of microbial populations and volatile fatty acid concentrations in the jejunum, ileum, and cecum of pigs weaned at 17 vs 24 days of age. J. Anim. Sci., 80(11):2904-2910.

[9]Gallo, L., Monta, G.D., Carraro, L., et al., 2014. Growth performance of heavy pigs fed restrictively diets with decreasing crude protein and indispensable amino acids content. Livest. Sci., 161:130-138.

[10]Gloaguen, M., Le Floc'h, N., Corrent, E., et al., 2014. The use of free amino acids allows formulating very low crude protein diets for piglets. J. Anim. Sci., 92(2):637-644.

[11]He, L.Q., Yang, H.S., Hou, Y.Q., et al., 2013. Effects of dietary L-lysine intake on the intestinal mucosa and expression of cat genes in weaned piglets. Amino Acids, 45(2):383-391.

[12]Hou, Z.P., Yin, Y.L., Huang, R.L., et al., 2008. Rice protein concentrate partially replaces dried whey in the diet for early-weaned piglets and improves their growth performance. J. Sci. Food Agric., 88(7):1187-1193.

[13]Hu, C.A., Khalil, S., Zhaorigetu, S., et al., 2008. Human ∆¹-pyrroline-5-carboxylate synthase: function and regulation. Amino Acids, 35(4):665-672.

[14]Jensen, B.B., 1998. The impact of feed additives on the microbial ecology of the gut in young pigs. J. Anim. Feed Sci., 7:45-64.

[15]Kang, P., Yin, Y.L., Ruan, Z., et al., 2008. Effect of repl 10.1002/jsfa.3298 16 J. Anim. Sci., 73(10):3000-3008.

[17]Kerr, B.J., Southern, L.L., Bidner, T.D., et al., 2003. Influence of dietary protein level, amino acid supplementation, and dietary energy levels on growing-finishing pig performance and carcass composition. J. Anim. Sci., 81(12):3075-3087.

[18]Lallès, J.P., Bosi, P., Smidt, H., et al., 2007. Nutritional management of gut health in pigs around weaning. Proc. Nutr. Soc., 66(2):260-268.

[19]Le Bellego, L., Noblet, J., 2002. Performance and utilization of dietary energy and amino acids in piglets fed low protein diets. Livest. Prod. Sci., 76(1-2):45-58.

[20]Liu, M.B., Li, X.L., Liu, Y., et al., 2014. Detection of crude protein, crude starch, and amylose for rice by hyperspectral reflectance. Spectrosc. Lett., 47(2):101-106.

[21]Liu, X.D., Wu, X., Yin, Y.L., et al., 2012. Effects of dietary L-arginine or N-carbamylglutamate supplementation during late gestation of sows on the miR-15b/16, miR-221/222, VEGFA and eNOS expression in umbilical vein. Amino Acids, 42(6):2111-2119.

[22]Nyachoti, C.M., Omogbenigun, F.O., Rademacher, M., et al., 2006. Performance responses and indicators of gastrointestinal health in early-weaned pigs fed low-protein amino acid-supplemented diets. J. Anim. Sci., 84(1):125-134.

[23]Opapeju, F.O., Rademacher, M., Blank, G., et al., 2008. Effect of low-protein amino acid-supplemented diets on the growth performance, gut morphology, organ weights and digesta characteristics of weaned pigs. Animal, 2(10):1457-1464.

[24]Opapeju, F.O., Rademacher, M., Nyachoti, C.M., 2009. Effect of dietary crude protein level on jejunal brush border enzyme activities in weaned pigs. Arch. Anim. Nutr., 63(6):455-466.

[25]Recktenwald, E.B., Ross, D.A., Fessenden, S.W., et al., 2014. Urea-N recycling in lactating dairy cows fed diets with 2 different levels of dietary crude protein and starch with or without monensin. J. Dairy Sci., 97(3):1611-1622.

[26]Skalli, A., Zambonino-Infante, J.L., Kotzamanis, Y., et al., 2014. Peptide molecular weight, distribution of soluble protein fraction affects growth performance and quality in European sea bass (Dicentracrchus labrax) larvae. Aquacul. Nutr., 20(2):118-131.

[27]Tan, B., Yin, Y., Liu, Z., et al., 2009. Dietary L-arginine supplementation increases muscle gain and reduces body fat mass in growing-finishing pigs. Amino Acids, 37(1):169-175.

[28]Tan, B., Yin, Y., Liu, Z., et al., 2011. Dietary L-arginine supplementation differentially regulates expression of lipid-metabolic genes in porcine adipose tissue and skeletal muscle. J. Nutr. Biochem., 22(5):441-445.

[29]Tuitoek, K., Young, L.G., de Lange, C.F., et al., 1997. The effect of reducing excess dietary amino acids on growing-finishing pig performance: an elevation of the ideal protein concept. J. Anim. Sci., 75(6):1575-1583.

[30]Wang, W., Gu, W., Tang, X., et al., 2009. Molecular cloning, tissue distribution and ontogenetic expression of the amino acid transporter b^0,+ cDNA in the small intestine of Tibetan suckling piglets. Comp. Biochem. Physiol. B Biochem. Mol. Biol., 154(1):157-164.

[31]Wu, G., 1998. Intestinal mucosal amino acid catabolism. J. Nutr., 128(8):1249-1252.

[32]Yao, K., Yin, Y., Li, X., et al., 2012. Alpha-ketoglutarate inhibits glutamine degradation and enhances protein synthesis in intestinal porcine epithelial cells. Amino Acids, 42(6):2491-2500.

[33]Yin, Y.L., Tan, B., 2010. Manipulation of dietary nitrogen, amino acids and phosphorus to reduce environmental impact of swine production and enhance animal health. J. Food Agric. Environ., 8(3-4):447-462.

[34]Yue, L.Y., Qiao, S.Y., 2008. Effects of low-protein diets supplemented with crystalline amino acids on performance and intestinal development in piglets over the first 2 weeks after weaning. Livest. Sci., 115(2-3):144-152.

[35]Zarate, A.J., Moran, E.T., Burnham, D.J., 2003. Reducing crude protein and increasing limiting essential amino acid levels with summer-reared, slow- and fast-feathering broilers. J. Appl. Poultry Res., 12(2):160-168.

[36]Zhang, J., Yin, Y.L., He, Q.H., et al., 2012. Effects of MSG supplementation on free amino acids in plasma of growing-finishing pigs. J. Food Agric. Environ., 10(3-4):600-605.

[37]Zhang, J., Yin, Y.L., Shu, X.G., et al., 2013. Oral administration of MSG increases expression of glutamate receptors and transporters in the gastrointestinal tract of young piglets. Amino Acids, 45(5):1169-1177.