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

## TL;DR

Adding arginine or N-carbamylglutamate to rabbit diets improves gut health and stress resistance in young rabbits.

## Contribution

This study demonstrates that dietary supplementation with arginine or NCG enhances jejunum development and stress tolerance in weaning rabbits.

## Key findings

- Arginine or NCG supplementation increased villus height and improved jejunum structure in young rabbits.
- Supplementation reduced crypt depth and increased the villus-to-crypt ratio, indicating better gut morphology.
- Arginine and NCG increased HSP70 mRNA expression and stress tolerance in the jejunum.

## Abstract

Rabbits are important economic and experimental animals. At present, the main challenge facing rabbit production is maintaining gut health during the post-weaning period. This study focused on the gut health of weaning rabbits by adding arginine (Arg) or N-carbamylglutamate (NCG) to their diet. The assessment was performed from jejunum development, focusing on stress-related indices. Adding 0.6% Arg or 0.06% NCG can improve jejunum morphological and structural development. They also up-regulated HSP70 mRNA expression, enhanced intestinal stress tolerance, and improved gut health. During the lactation period, adding 0.6% Arg or 0.06% NCG increased the GABR, but GABR was <0.8 during weaning, which could be crucial for predicting diseases and also reflect the effect of arginine or NO on the body.

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 (p < 0.05) and was highly significantly improved in the 0.6% Arg group (p < 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 (p < 0.05). Compared with the con group, the V/C ratio was significantly increased in the treatment groups (p < 0.05) and was excessively and significantly increased in the 0.6% Arg and 0.06% NCG groups (p < 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 (p > 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 (p < 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 mRNA expression levels of heat shock protein 70 (HSP70) in the jejunum (p < 0.05). The expression level in the 0.6% Arg and 0.06% NCG groups was significantly higher than that in the con group (p < 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 mRNA expression, promoting NO synthesis. Thus, it can improve jejunal morphological and structural development. Adding Arg or NCG increased HSP70 mRNA 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.