1. Department of Animal Sciences, Purdue University, West Lafayette, IN 47906, USA.
2. USDA-ARS Livestock Behavior Research Unit, West Lafayette, IN, 47907, USA.
3. Department of Agriculture, Food, Environment and Forestry (DAGRI), University of Florence, 50144 Firenze, Italy.
4. Smithfield Premium Genetic, Rose Hill, NC 28458, USA.