The large confinement operations have actually bred out a stress gene that was causing an average 14 per cent mortality from crowding and shipping stresses. This is not an issue for pastured pigs that are properly managed, as the stress gene is managed with adequate space between sows and two of a pigs traits rooting and foraging.

Rooting is strong stress reducer among pigs, and they should be spending about 50 per cent of their active time doing this. Deep bedding in the nests and winter housing helps maintain this behavior and putting hogs on hard pack areas and confined areas (concrete, etc.) denies them this activity and leads to increased stress. On the other hand, foraging – looking for food and eating grass, legumes and roots – is a social activity when the pastured area is big enough for all to get their share of a wide enough range of food.

Swine herds are matriarchal in nature. There is a strong hierarchical structure among the females and the lead, or ‘alpha’ sow, is the gatekeeper and nests closest to the feeders and water trough. The lowest ranking female in the herd nests the furthest away. Having said that, some characteristics you need to look for in selection among the gilts include the following:

• Hardiness to climate extremes cold and heat. The heat stressor is critical and can be augmented by the mother’s ability to wallow, which is a heat reduction and external parasite coping trait.
• Mothering attributes would be supported by your record-keeping of the sows, including number of piglets born per litter, number of piglets successfully weaned (difference would be mortality figures from your records). Also consider the rate of gain, and weight per unit of feed.
• Nesting and farrowing traits, which are strongly heritable. In Berkshire, Tamworth, Chester Whites, Hereford, and large blacks breeds, these traits are well established.
• Physical confirmation and soundness traits. These include selecting from maternal and boar lines that have a low incidence of rhinitis and also good leg strength in sows for breeding and “lock-up” during standing heat.

Ideally, a bred female should be able to pick a nest site and build a nest away from the more dominant sows in under five hours. The time is critical in order for the sow to go into farrowing cycle with adequate rest and not be too stressed. This also means that there needs be adequate supply of nesting materials such as straw already on hand in the pasture. Inadequate nesting materials leads to stress, lower birth rates, and higher mortalities.

To learn more about raising hogs, check out the Hogs section of the ATTRA web site.

October 2014