Egg Production Performance and Thyroid Transcriptome Characteristics of Two Chicken Breeds Under Cold and Warm Environment

Cold environments adversely affect egg production, health, and welfare of chickens. The thyroid gland produces two hormones, triiodothyronine (T3) and thyroxine (T4), which control the metabolic rate of the body. The Bashang long-tail chicken (BS), a cold tolerant Chinese indigenous chicken breed, and the Rhode island red (RIR) were used in the present study. The egg production performance, serum thyroid hormones levels, and thyroid transcriptome profile were investigated under both cold and warm environments. Four 39-week old birds from each breed in cold and warm environments were randomly selected for thyroid sampling and RNA-seq. BS showed superior egg production performance and higher thyroid hormone levels compared to RIR, as well as stable body weight increases, under cold conditions, which verified its remarkable cold tolerance. Analysis of RNA-seq data showed that BS thyroid had higher immune cell activity under both cold and warm environments, which may influence thyroid function and serum thyroid hormone levels. In the cold environment, BS thyroid showed increased activity in sterol biosynthesis and metabolic processes, which suggests that enhanced lipid biosynthesis and metabolism is a critical cold adaptation mechanism. To our knowledge, this is the first transcriptomic study of chicken thyroid function, generating information that provides a platform for future studies of cold-tolerance mechanisms and for its selection.