1. Introduction
Deep-litter, large group systems have been developed as an alternative housing system for growing pigs. These systems are cheaper to establish and are perceived as being more welfare friendly for pigs, compared to conventional housing systems. Deep-litter, large group systems offer more pen space per pig (approximately 1 m2 per pig), larger group sizes (ranging from 150 to 2000 pigs per pen), an enriched environment (an environment which provides an outlet for
rooting and foraging in deep bedding), together with the opportunity for increased social interaction among pigs (Morrison et al., 2003a,b). Conventionally, pigs are housed in more confined systems with fully, or partially slatted floors, liquid effluent system, group sizes ranging from 5 to 50 pigs with a floor space allowance of approximately 0.7 m2 per pig.