Pig production contributes importantly to environmental pollution through the emission of nitrogen waste. Many countries cannot meet the plant-protein demand of livestock with current feed cultivation practices, and an important part of high-quality protein feed, most importantly soybean meal, is imported from South America. The high global demand for protein results in an increased competition of agricultural land for human food and animal feed and ultimately to the large-scale loss of ecological habitats. It is therefore desirable to improve protein efficiency, i.e. the proportion of dietary protein that is fixed in the body, of pigs, an important livestock species, through selective breeding. However, little is known about the inheritance pattern and genetic architecture of protein efficiency as well as the genes underlying protein efficiency and their functions, which is essential for assessing the potential to breed pigs with higher protein efficiency.