Supplementation of Arginine or N-Carbamylglutamate Affects Jejunum Development, Global Arginine Bioavailability Ratio, and Stress-Related Indices in Young Rex Rabbits

This study aimed to investigate the effects of arginine (Arg) or N-carbamylglutamate (NCG) on jejunum development, the global arginine bioavailability ratio (GABR), and stress-related indices in young rex rabbits. Forty-five litters of newborn rabbits with similar litter weights and sizes were randomly divided into five groups and fed a basal diet (con group), basal diet + 0.3% Arg (0.3% Arg group), basal diet + 0.6% Arg (0.6% Arg group), basal diet + 0.03% NCG (0.03% NCG group), or basal diet + 0.06% NCG (0.06% NCG group). After weaning at 35 days, eight healthy young rabbits with similar body weights were selected from each group and slaughtered on the 36th day. Serum and jejunum samples were collected for index analysis. Arg or NCG significantly affected the jejunum structure development in the young rabbits. The villus height (V) in the treatment groups was significantly higher than that in the con group (<i>p</i> < 0.05) and was highly significantly improved in the 0.6% Arg group (<i>p</i> < 0.01). The crypt depth (C) in 0.6% Arg and 0.06% NCG groups was significantly lower than that in the con, 0.3% Arg, and 0.03% NCG groups (<i>p</i> < 0.05). Compared with the con group, the V/C ratio was significantly increased in the treatment groups (<i>p</i> < 0.05) and was excessively and significantly increased in the 0.6% Arg and 0.06% NCG groups (<i>p</i> < 0.01). Compared with the con group, the Nitric-Oxide (NO) levels and inducible Nitric-Oxide Synthase (iNOS) activity in serum were significantly increased in the treatment groups. The NO levels in the jejunum were also increased in the treatment groups; however, there were no significant differences (<i>p</i> > 0.05). The iNOS activity and mRNA expression in the jejunum of the 0.6% Arg and 0.06% NCG groups were significantly higher than those in the con group (<i>p</i> < 0.05). Compared with the con group, the concentration of serum corticosterone in the 0.3% Arg, 0.6% Arg, and 0.06% NCG groups was significantly reduced. Adding Arg or NCG to the basal diet significantly increased the concentration and gene <i>mRNA</i> expression levels of heat shock protein 70 (HSP70) in the jejunum (<i>p</i> < 0.05). The expression level in the 0.6% Arg and 0.06% NCG groups was significantly higher than that in the con group (<i>p</i> < 0.01). At 36 days, Arg and NCG improved the GABR. In the 0.6% Arg group, the GABR was increased by 16.92%. The GABR was <0.8 at the time of weaning. The Arg levels in the body did not meet the needs of the young animals. In the trial, Arg or NCG supplementation in the diet significantly increased iNOS activity and gene <i>mRNA</i> expression, promoting NO synthesis. Thus, it can improve jejunal morphological and structural development. Adding Arg or NCG increased HSP70 <i>mRNA</i> expression levels, enhanced intestinal stress tolerance, and improved intestinal health. During the lactation period, adding Arg or NCG increased the GABR, but the GABR was <0.8 during weaning.