1. Department of Veterinary Clinical Sciences, Purdue University, West Lafayette, IN 47907-2026, USA
2. Center for Applied Ethology and Human–Animal Interaction, Purdue University, West Lafayette, IN 47907-2026, USA
3. P&G Pet Care R&D, Lewisburg, OH 45338-0189, USA
4. Department of Veterinary Pathobiology, Purdue University, West Lafayette, IN 47907-2026, USA