Ovine IL-17A (Interleukin-17A) is a pro-inflammatory cytokine belonging to the IL-17 family that plays a key role in host defense and inflammatory responses in sheep (Ovis aries). IL-17A is produced primarily by Th17 CD4⁺ T cells, as well as by γδ T cells—which are prominent in ruminants—and other innate lymphoid cell populations in response to microbial infection and immune stimulation. It acts on epithelial, endothelial, and stromal cells to induce expression of pro-inflammatory cytokines (such as IL-6 and TNF-α), chemokines (including CXCL8), and antimicrobial peptides, thereby promoting neutrophil recruitment and enhancing mucosal and barrier immunity in respiratory, gastrointestinal, and mammary tissues. In healthy sheep, basal IL-17A expression is generally low, but levels increase during bacterial and fungal infections, mastitis, respiratory disease, and parasitic challenges, particularly gastrointestinal nematode infections such as Haemonchus contortus. In veterinary and agricultural research, ovine IL-17A serves as an important biomarker of Th17-mediated immune activation and neutrophilic inflammation, providing insight into host–pathogen interactions, vaccine responses, and immune regulation in small ruminant health and production systems.