Abstract
Background: Orange peel waste (OPW) is an unconventional agro-industrial by-product that has attracted considerable attention as a functional feed ingredient because of its nutritional value and rich content of bioactive compounds. Its dietary inclusion has been suggested to improve growth performance, antioxidant status, immune response, and tissue health in rabbits.
Aim: This study aimed to evaluate the effects of dietary supplementation with OPW at inclusion levels of 5% and 10% in isonitrogenous and isocaloric diets on growth performance, blood biochemical parameters, oxidative status, immune response, and gene expression in growing New Zealand White rabbits.
Materials and Methods: Twenty-four healthy weaned New Zealand White rabbits were randomly allocated into three experimental groups (n = 8 per group). The control group received a basal diet, whereas the other two groups were fed diets supplemented with 5% or 10% orange peel waste (OPW) for 6 weeks. Growth performance and feed utilization were evaluated weekly. At the end of the experiment, blood and tissue samples were collected for biochemical, antioxidant, immune, oxidative stress, and gene expression analyses.
Results: Dietary supplementation with orange peel waste improved growth performance and feed utilization compared with the control group. OPW supplementation also improved the serum lipid profile by reducing total cholesterol, triglycerides, and low-density lipoprotein while increasing high-density lipoprotein levels. Antioxidant capacity was enhanced, particularly in the 10% OPW group. Furthermore, OPW enhanced humoral immune response, upregulated genes associated with growth, antioxidant defense, and immune function, especially in rabbits receiving 10% OPW.
Conclusion: Dietary supplementation with orange peel waste, particularly at the 10% inclusion level, demonstrated beneficial effects on growth performance, feed efficiency, lipid metabolism, antioxidant defense, immune response, and gene expression, in growing New Zealand White rabbits.

Key words: Orange peel waste; New Zealand White rabbits; growth performance; antioxidant status; gene expression.