Texas A&M Univ, Dept Anim Sci, College Stn, TX 77843 USA.^Chinese Acad Sci, Inst Subtrop Agr, Lab Anim Nutr & Hlth, Changsha 410125, Hunan, Peoples R China.^Chinese Acad Sci, Inst Subtrop Agr, Key Lab Subtrop Agroecol, Changsha 410125, Hunan, Peoples R China.^Chinese Acad Sci, Inst Subtrop Agr, Lab Anim Nutr & Hlth, Changsha 410125, Hunan, Peoples R China.^Hunan Agr Univ, Coll Anim Sci & Technol, Changsha 410128, Hunan, Peoples R China.^Sichuan Agr Univ, Inst Anim Nutr, Yaan 625014, Sichuan, Peoples R China.^Univ Guelph, Ctr Nutr Modelling, Dept Anim & Poultry Sci, Guelph, ON N1G 2W1, Canada.