In indoor intensive systems, pregnant gilts/sows (female pigs) are moved to a farrowing crate, also known as a piglet protection pen, approximately a week before farrowing (giving birth) . Farrowing crates confine sows so that they are unable to turn around. Some indoor systems may have farrowing pens which can be adjusted to either provide the sow freedom to move or be confined to protect piglets from being crushed. The confinement of sows is intended to protect piglets from being crushed, particularly during farrowing (birthing) and the following few days when the risk of crushing is high. Farrowing crates, and the ability to confine the sow, allows easy access to piglets for routine husbandry procedures that commonly occur in their first few days of life.
In outdoor extensive systems, pregnant gilts/sows are moved to farrowing huts located in an outdoor area or paddock. The farrowing huts are usually bedded with straw and are big enough to allow the female pig to turn and walk around easily. Some huts may also have guards around the front of the hut that sows can easily step over to get outside but keeps piglets in the hut during their first few days or weeks of life.
Farrowing crates confine the sow but give piglets room to access the udder, as well as a separate creep area away from the sow to keep them warm and protected, whereas farrowing huts allow the sow and her piglets (from around 1-2 weeks of age) to access the outdoor area. The sow has access to the farrowing hut or remains in the farrowing crate for 3-4 weeks after farrowing, at which time her piglets are weaned and moved to weaner housing. After weaning, the sow will usually come back ‘on-heat’ (be fertile) within a few days. At this point, the sow is mated again through artificial insemination which usually involves being confined in a mating stall for several days, and is then returned to group housing.
In indoor systems, weaned piglets are grown out in group pens with concrete floors or slats with or without bedding. In semi-indoor systems (outdoor bred or bred free range), the piglets grow out in large, deep-bedded shelters (also known as ecoshelters) with bedding (such as straw or rice hulls). Whereas in outdoor systems (free range), weaned piglets may be raised in similar bedded shelters but with an outdoor area attached or in outdoor areas with smaller shelters.
 Australian Pork: Our Farming Systems (2020)