1. Department of Animal Science, Texas A&M University, College Station, TX 77843, USA
2. Department of Epidemiology and Biostatistics, Texas A&M University, College Station, TX 77843, USA
3. Department of Epidemiology and Biostatistics, School of Public Health, Indiana University, Bloomington, IN 47403, USA
4. Department of Medical Physiology, Texas A&M University, College Station, TX 77843, USA