Thymus Gland Development in White Leghorn Chickens: A Gross and Biometrical Evaluation from Hatching to 24 Weeks

The study was conducted from March to November, 2024 in the Department of Veterinary Anatomy & Histology, College of Veterinary Science & Animal Husbandry, Central Agricultural University, Mizoram, India to investigate the thymus gland development in White Leghorn Chickens from hatching to 24 weeks of age. The twenty-one (21) numbers of experimental birds were divided into seven (7) age-groups, at 4 weeks interval, consisting of three (3) numbers of birds in each group. After collection, the birds were sacrificed by the cervical dislocation method at their respective age and the thymus glands were collected. Along with morphological parameters the biometrical parameters like weight, length, width and thickness were also recorded. The left thymus was deeply situated near the esophagus, trachea, blood vessels, and nerves, whereas the right thymus was positioned closer to the skin and away from cervical structures, extending from the third cervical vertebra to the upper thoracic region. The thymus of all White Leghorn Chickens appeared light pink to creamy white in colour, regardless of their age and bean or button-shaped, and soft in texture. The body weight of White Leghorn chickens increased steadily from hatching to 24 weeks, while thymus weight rose until 12 weeks before gradually declining. Thymus weight, width, and thickness peaked at 12 weeks, with the right thymus reaching maximum length at 12 weeks and the left at 20 weeks. The highest number of lobes was observed at 8 and 16 weeks, and by 24 weeks, thymic involution was complete, with lobes replaced by adipose tissue. It was also noted that the thymus thickness increased from 0 day to 12 weeks, reaching its maximum thickness on both sides.