This investigation provides a comprehensive anatomical, histological, and endocrine profile of the thyroid gland in adult guinea fowls (Numida meleagris), a species for which detailed morphological data remain scarce in avian literature. A total of ten clinically healthy specimens, representing both sexes, were subjected to morphometric analysis of their thyroid glands, including lobar dimensions and weight. Anatomical dissection revealed that the glands are bilaterally positioned at the thoracic inlet, symmetrically located near the carotid arteries. Histological examinations—conducted using Hematoxylin and Eosin and Masson\'s trichrome stains—demonstrated the presence of structurally uniform follicles surrounded by a highly vascularized stroma rich in collagen fibers and smooth muscle bundles. Parafollicular (C) cells appeared sporadically within the interfollicular matrix and exhibited mild affinity to periodic acid–Schiff staining. Distinct variations in follicular dimensions were noted between the two lobes, suggesting lateralized functional asymmetry. Quantification of circulating thyroid hormones, performed via ELISA, yielded the following mean values: T3 at 72.80 ± 10.7 pg/mL, T4 at 158.95 ± 7.4 pg/mL, and TSH at 1059.52 ± 81.4 pg/mL. These endocrine values indicate a physiologically active hypothalamic–pituitary–thyroid axis. A strong positive correlation was also observed between body mass and total thyroid weight, implying adaptive regulation of glandular mass in response to metabolic demand. Collectively, these findings contribute to a deeper understanding of the species-specific thyroid architecture and hormone dynamics in guinea fowl, with broader implications for comparative avian endocrinology and evolutionary morphology.
