Outdoor pig production systems come in many forms. In some European countries, particularly UK and France, there are significant numbers of outdoor herds contributing to conventional pig meat supplies. In the UK, it has been estimated that approximately 30% of the national sow breeding herd is housed outdoors (Sheppard, 1996) although this figure is
lower in other European countries (Edwards, 1994). The popularity of outdoor production is a consequence of financial considerations linked to the low establishment and overhead cost of such systems (Edwards, 1996), as well as encouragement from retailers with a market for more extensively produced meat. These conventional outdoor production systems typically have highly selected genotypes, high stocking rates, and total reliance upon manufactured compound feed. However, they are seldom truly outdoor systems for the meat animals; they typically confine the progeny after weaning, sometimes in hit and- run outdoor systems and more often in fully enclosed buildings. Finishing pigs are almost always housed, either in deep litter systems or in conventional controlled environment housing, with b0.5% of UK pigs being finished outdoors (Sheppard, 1996; Edwards, 1999b).