Background Epidermal growth factor (EGF) is a multifunctional polypeptide, which could be utilized to solve problems in the industry such as increasing growth performance of commercial broilers or enhancing resistance to diseases under adverse conditions. Thus far, very few studies have focused on the gallus epidermal growth factor (gEGF) despite the availability of a plethora of studies on mammalian EGF. The aim of this study was to express gallus epidermal growth factor (gEGF) using a food-grade Lactococcus lactis expression system and to investigate its biological effects on broiler chickens. Results A recombinant Lactococcus lactis, which produced the secretary form of bioactive gEGF at 2.67 μg/mL in culture supernatant, was generated. In vitro testing denoted that gEGF promoted the proliferation of UMNSAH/DF-1 cells. Sixty-three 5-day-old broiler chickens were divided into three groups and treated with either M17 medium (C, as control), supernatant of LL-pNZ8149 fermentation product (P-LL), or supernatant of LL-pNZ8149-gEGF fermentation product (gEGF-P-LL). Body weight (BW), average daily gain (ADG), and the gain:feed ratio of the gEGF-P-LL group were significantly higher than those of the other groups during the two-week study. In addition, two weeks after therapy, the indices of spleen and thymus gland, levels of serum IgA, IgG and duodenum mucosal sIgA were all significantly higher in the gEGF-P-LL group than in the other groups. Moreover, the villus height of the duodenum, jejunum and ileum and crypt depth of the jejunum of the gEGF-P-LL group were significantly higher than those of the other groups, while the crypt depth of the duodenum showed the opposite pattern during the two-week study. Conclusions The bioactive gEGF could be expressed with Lactococcus lactis expression system. Furthermore, gEGF has the potential to enhance growth performance, immune function, and intestinal development in broiler chickens.