Effects of Alanyl-Glutamine Dipeptide Supplementation on Growth Performance, Nutrient Digestibility, Digestive Enzyme Activity, Immunity, and Antioxidant Status in Growing Laying Hens

Alanyl-glutamine (<b>Aln-Gln</b>), a highly soluble and stable Glutamine-dipeptide, is known to improve the performance of poultry birds. This study aimed to investigate the effect of Aln-Gln during the rearing period on growth performance, nutrient digestibility, digestive enzyme activity, immunity, antioxidant status and relative gene expression of <i>Hy-Line</i> brown hens. A total of 480 healthy day-old <i>Hy-line</i> brown chicks with similar body weights were randomly divided into four dietary groups (8 replicates/group and 15 birds/replicate). Groups A, B, C and D were fed diets containing 0%, 0.1%, 0.2% and 0.3% Aln-Gln, respectively, for 6 weeks. The body weight (<b>BW</b>) and average daily gain (<b>ADG</b>) were higher in hens fed test diets compared with the control (<i>p</i> < 0.05). The feed conversion ratio (<b>FCR</b>) was better in test groups as compared to the control group (<i>p</i> < 0.05). The ADFI showed no significant difference between the groups. Dietary treatments had no effect on dry matter (<b>DM</b>), organic matter (<b>OM</b>) and crude fiber (<b>CF</b>) digestibility. The Aln-Gln also improved gross energy (<b>GE</b>) and crude protein (<b>CP</b>) digestibility (<i>p</i> < 0.05). It has also increased IgG levels in groups C and D. IgM levels were similar to the control in B, C and D. The Aln-Gln increased IL-1 in B and C, IL-2 in C and D, and IL-6 in all test groups (<i>p</i> < 0.05). The supplementation of Aln-Gln had no effect on serum antioxidant indices like CAT, MDA, GSH-PX, GSH, and SOD in 42-day-old growing hens. Aln-Gln supplementation had no significant effect (<i>p</i> > 0.05) on the activity of amylase and lipase, however, a significant improvement (<i>p</i> < 0.05) in the activities of trypsin and chymotrypsin was observed in the test groups. Supplemented Aln-Gln levels in the birds' diets led to an increase in the expression of genes related to growth factors (IGF-1, IGFBP-5), immune markers (IL-1, IL-2, IL-6) and antioxidant status (GSH-Px1), as compared to control group. Aln-Gln supplementation in <i>Hy-Line</i> brown hens during their growing period improved growth, nutrient digestibility, immunity and digestive enzymes activity. These findings suggest that Aln-Gln is a promising dietary additive for enhancing poultry performance.