1. Coll. of Animal Sciences and Technology; Huazhong Agricultural Univ.; Wuhan 430070 China
2. Cooperative Innovation Center for Sustainable Pig Production; Wuhan 430070 China
3. Hubei Provincial Engineering Lab. for Pig Precision Feeding and Feed Safety Technology; Wuhan 430070 China
4. Dept. of Agricultural, Food and Nutritional Science; Univ. of Alberta; Edmonton Alberta T6G 2P5 Canada