Comprehensive transcriptomic and metabolomic analysis of the effect of feed restriction on duck sternal development

Skeletal characteristics are important to the growth and development of poultry. In feeding management, constant free feeding (FF) of poultry may lead to imbalance between bone development and weight gain. Feed restriction (FR), to a certain extent, is one way to solve this problem. However, the effect of feed restriction on poultry bone development needs further elucidation at the molecular level. Therefore, in the present study, we investigated the effects of different levels of feed restriction (60% FR, 70% FR, 80% FR, and FF) on the sternum development of ducks at 7 and 8 wk old. In the seventh wk, with increasing feed restriction, the values of traits including body weight, breast muscle weight, sternal weight, keel length, and calcified keel length decreased. However, in the eighth wk, the sternum weight and keel length of ducks treated with 60% FR were unexpectedly higher than those of FF individuals, indicative of catch-up growth. Then, we conducted RNA-seq and metabolomic analysis on sterna from 7- and 8-wk-old FF and 60% FR ducks. The results identified multiple differentially expressed genes (DEGs) associated with sternum development that were influenced by feed restriction. Among them, we found that the mRNA expression levels of the chondroitin sulfate synthase 3 (CHSY3) and annexin A2 (ANXA2) which are involved in glycosaminoglycan biosynthesis and bone mineralization, had smaller changes over time under FR treatment than under FF treatment, implying that the FR treatment to a certain extent prevented the premature calcification and prolonged the development time of duck sternum. In addition, the metabolomic and integrative analyses revealed that several antiaging-related metabolites and genes were associated with sternal catch-up growth. Pyrimidine metabolism was identified as the most significant pathway in which most differential metabolites (DMs) between FF and 60% FR were enriched. The results from integrative analysis revealed that the content and expression of 4-aminobutyric acid (GABA) and its related genes showed relatively higher activity in the 60% FR group than in the FF group. The present study identifies multiple biomarkers associated with duck sternum development that are influenced by feed restriction and suggests the potential mechanism of feed restriction-associated duck sternal catch-up growth.