The present study investigated the effects of partially replacing conventional protein sources (CPS) with Spirulina platensis powder (SPP) on growth performance, immune response, physiological traits, histomorphology, and economic efficiency of broiler chickens. A total of 240 one-day-old male Cobb500 chicks were allotted to 24 cages and fed a starter diet from days 1 to 13. From days 14 to 35, birds were randomly assigned to four dietary treatments (six replicates each): a CPS-based finisher diet replaced with 0%, 5%, 10%, or 15% SPP. Growth performance parameters exhibited significant quadratic responses to SPP inclusion (P<0.05), with 10% SPP producing the highest BW, weight gain, feed efficiency, and production index. Regarding the immune response, leukocyte counts and lymphocyte proliferation increased linearly, while leukocyte viability, anti-SRBC antibody titers, phytohemagglutinin response, and heterophil-to-lymphocyte ratio improved quadratically, reaching a peak at 10% SPP. A linear increase in total antioxidant capacity and reduced glutathione, along with a corresponding linear decrease in malondialdehyde and pro-inflammatory cytokines, was observed following SPP treatment. Plasma T3 displayed a quadratic increase, with the highest value at 10% SPP. ALT, creatinine, and urea were linearly declined, while triglycerides and cholesterol were linearly increased by the SPP treatment. Histological evaluation revealed normal liver and intestinal architecture, with only mild alterations at 15% SPP. Economically, SPP reduced feed and protein costs linearly, while net profit was maximized at 10% SPP. In conclusion, SPP is a functional and sustainable protein source for broilers, with a 10% inclusion level providing optimal biological and economic outcomes.

To Cite This Article: Alaqil AA, Al-Khalaifah H, Al-Suwailem NK, Kamel NN and Abbas AO, 2026. Spirulina platensis as a sustainable protein source: Impacts on broiler growth performance, immunity, physiology, and profitability. Pak Vet J, 46(3): 645-652. http://dx.doi.org/10.29261/pakvetj/2026.053