1. Department of Crop and Soil Science, University of Georgia, Tifton, GA 31793, USA
2. Department of Animal Science, Sul Ross State University, Alpine, TX 79830, USA
3. Facultad de Zootecnia y Ecología, Universidad Autonoma de Chihuahua, Chihuahua 31453, Mexico
4. Department of Veterinary Science, University of Kentucky, Lexington, KY 40506, USA