The physiology of leptin in avians: A review.

Leptin, discovered in 1994 in ob/ob and db/db mutant mice, is a key regulator of energy balance, appetite, and multiple physiological systems including immunity and reproduction. While its function in mammals is well-established, leptin's presence and role in birds remain controversial due to differences in gene sequence, tissue expression, and signaling mechanisms. Avian leptin exhibits a GC-rich sequence, predominates in autocrine and paracrine signaling, and maintains conserved receptor-binding residues, supporting functional activity despite low systemic levels. Experimental studies show leptin influences feed intake, immune function, and reproduction, though conflicting results have fueled ongoing debate. In this review, we discuss evidence supporting and questioning avian leptin function and highlight emerging gene-editing approaches, including CRISPR/Cas9-mediated manipulation of leptin and its receptor in poultry, as powerful tools to clarify its functional dynamics in vivo, resolve longstanding uncertainties, and potentially enhance poultry growth and production efficiency.