Abstract: Adipose tissue of mammals can be divided into white adipose tissue and brown adipose tissue. Brown adipose tissue and white adipose tissue are different in cell morphology and function, which play an important role in heat production and energy balance in mammals. In order to investigate the distribution characteristics of brown adipose tissue in sheep, perirenal fat, cervical fat, dorsal fat, tail fat, sternal fat, inguinal fat and pericardial fat of Sonid lamb at the 1 day, 7 day and 30 day after birth were collected. Different fat types were identified by HE staining, transmission electron microscope and immunohistochemical; And the characteristics of brown adipose tissue at different parts and different ages of Sonid lambs were explored by real-time fluorescent quantitative PCR and Western blot. The results showed that there were two different types adipocytes in Sonid lambs, brown adipocytes with small lipid droplets and white adipocytes with vacuolar lipid droplets. There were more mitochondria with cristae in brown adipocytes, and the expression of brown adipose tissue-specific protein UCP1 was detected. White adipocytes, on the other hand, had few mitochondria with regular cristae and did not express UCP1. Brown adipocyte numbers and UCP1 expression were not significantly different at 1 and 7 days of age, and decreased significantly at 30 days of age. In this study, the brown fat and white fat of Sonid lambs were identified by morphological observation, marker gene and protein detection, and it was proved that perirenal fat and tail fat were the main sources of brown fat and white fat, respectively. Sonid lambs had more brown fat at 1 and 7 days of age, and the phenotypic changes of brown fat at 30 days of birth showed a decreasing trend. The current study explored the characteristics of brown fat in Sonid lamb, and provided a certain basis for the study of brown fat in ruminants.

Key words: Sonid lambs, brown adipose tissue, distribution characteristics, UCP1