1. Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg 24060
2. Institute of Biological, Environmental and Rural Sciences, Aberystwyth University, Ceredigion, Wales, SY23 3DA, United Kingdom
3. ADAS Rosemaund, Preston Wynne, England, HR1 3PG, United Kingdom
4. Sustainable Livestock Systems Group, Scottish Agricultural College (SAC), West Mains Road, Edinburgh, Scotland, EH9 3JG, United Kingdom