The original gated stall system, in use before the industry adopted gestation stalls, has manually operated gates used to lock the sows into the stall only during feeding. At other times the gates are open and sows are free to come and go. This system is sometimes called a lock-in system.
In order to eliminate the need to have someone present during feeding, gating systems have been developed that can be controlled by the sow herself. If no sow is in the stall, the gate is open and any animal in the group can enter. Upon entering the stall, the gate is engaged and closes behind the animal by a cantilever mechanism. The gate locks and cannot be opened by any sow outside the stall, thus preventing the chance of food stealing or displacements. The sow inside the stall can open the gate, usually by backing against it, and is free to leave. These stalls are sometimes also called free-access or walk-in/lock-in stalls.
Unless otherwise specified, our comments in this article refer to these walk-in/lock-in stalls.
A third arrangement of gated stalls has arisen in order to reduce the space and cost of the system. In a cafeteria arrangement all of the sows in a group eat at the same time from a bank of lock-in stalls. When one group has finished feeding, they are moved out and a second group of sows is fed from the same bank of stalls. Rather than providing a feeding stall for each sow in a herd of 100, a single bank of 20 could be used to feed 5 groups of 20 during the day. This arrangement involves reduced installation costs, and provides protection whilst feeding, however, obviously there is an increased labour cost. A large scale cafeteria system has been studied in Australia (Karlen et al., 2007).
Keys to Success of Free-Access Stalls
Gated systems are an opportunity to buy success through design rather than management. Nonetheless, a few management practices will contribute to the smooth operation of the system:
- Maintain the gates so that they are easily opened by all sows when exiting the stall. Training of new sows may be helpful.
- Make the loafing area as conducive to sow use as possible, by providing adequate space, water, fibre, and comfortable floors.
- In large herds, sort the sows by age so that younger animals use the loafing area as well.
- Remove despot sows that constantly at tack other animals in the loafing area.
Control over feed intake
Because we limit feed sows, we are also very concerned about how well we can manage their feed intake. Competitive systems allow us to control the amount of feed that a pen of animals consumes, but not the amount that each individual sow will eat. With gated stalls, we know how much feed each animal will consume. But because we do not know which sow will be in which stall at feeding, the best we can do is to divide the feed evenly among the sows. All animals will eat the same amount. This brings about two important management methods for adjusting feed according to the requirements of different sows. The fi rst is to form groups based on desired feeding level: thin sows together and fat sows together. The second is to regularly provide additional feed, by hand feeding, to those sows needing more. For example, thin sows can be identified using stock marker, allowing the stockperson to top up those stalls very quickly.
Communal Loafing Space
Typically, free access stalls are arranged in one of several possible configurations. The two primary ones are the ‘I-pen’ or ‘I’, and the ‘T-pen’ or ‘T’ configurations. The ‘I-pen’ consists of an alley with slatted flooring running between two lanes of stalls from which open to the alley. The alley is typically 3 m (10 ft) wide. The length of the alley depends on the number of width of the feeding stalls. The ‘T-pen’ configuration consists of an identical alley with an additional solid floor area at one end of the pen. The ‘T’ typically adds at least 3 m (10 ft) to the overall length of the pen. The ‘T’ area may be bedded with straw, and is sometimes lower than the ‘I’ portion of the loafing area to retain straw on its solid floor.
Some producers may be tempted to reduce with width of the free space area between the two rows of stalls, however this is counter intuitive. It is not only important that we provide free space outside of the stalls, but the space must be of sufficient quality i.e. adequate flooring, adequate space to avoid aggressive encounters etc, and to increase usage, it would also be advised to provide some sort of enrichment, and water drinkers etc. It is very important that two sows from either row of stalls can exit their stalls without having to maneuver around one another and possibly having to avoid an aggressive encounter.
Use of Communal Loafing Space
Part of the rationale for group housing systems is that the animals benefit from increased exercise and social interactions. Studies demonstrated that sows in an ESF system were found to have increased bone strength and decreased muscular atrophy than those housed an equal period of time in gestation stalls (Marchant and Broom, 1996). Yet one of the greatest criticisms of the walk-in/ lock-in stall system is that sows spend most of their time within the stall. Our own observations, in a typical non-bedded free access system, is that using the loafing area is highly variable among the sows (Lang et al., 2010). Although the average amount of time.
spent outside the stall is approximately 4 hours, some sows may not leave the stall at all during the day and others will be out more than 20 hours. The sows least likely to be outside the stall are the smaller, younger sows, while larger, older (dominant) sows, spend the most time in the loafing area. We hypothesize three possible reasons for this. The smaller sows may be intimidated by the larger, dominant sows; the larger sows may be more uncomfortable in the gestation stalls; and, the smaller sows may have difficulty opening the back gate of the stall due to their size or lack of training.
Use or non-use of the loafing area will be dependent upon the relative costs and benefits of leaving the stall. The costs will include the social tension of interacting with other animals, while the benefits may include issues of comfort and access to resources. Many existing free access systems provide little incentive to use the loafing area. All resources (food and water) are provided in the stall, and the loafing area consists of spindle walls, slatted floors and no bedding or enrichment devices. Why would a sow spend a great deal of time in what would be a relatively uncomfortable environment?
Two general methods may be used to encourage sows to increase the use of the loafing area, and thus increase the exercise that they experience. The first is to provide resources outside the stall such that animals will exit at least once a day to access them. An obvious choice would be to provide water in the loafing area but not in the stall. This would require that we have a great deal of confidence in the gate locking system that sows could easily leave the stall at any time. As mentioned above, there is some concern that not all systems are easy to open by small sows. Another resource that sows would likely access would be sources of fibre, such as chopped straw or a hay rack.
A second means to increase use of the loafing area would be to improve comfort in the area. For example, sows prefer to rest against solid walls rather than spindle penning and solid floors are preferred to slatted. In many ‘T’ systems, the ‘T’ section is bedded with straw. Nielsen (2008) indicates that 50-75% of sows use the ‘T’ section, but is it unclear if this refers to the average proportion of sows using it at any time, or those that use it at least once per day
What Role Does Competition Play?
Gated stalls are the least competitive of all the group housing systems. A sow need only enter the feeding stall and she is protected from the remaining sows in the group. This is true both during feeding, and during social interactions in the loafing area. The stalls provide an escape from aggression. But competition remains for other resources within the pen. If water, a straw rack or some form of enrichment is available in the loafing area, the dominant sows will have preferred access to it. Dominant sows will make use of preferred lying areas, whether they are against the wall of the loafing area or areas with straw or rubber mats. Subordinate sows will be relegated to slatted areas and thus may have a higher incidence of ‘discomfort’ injuries such as lameness or calluses. In some groups, the dominant animal may be a despot and attack all other sows with little regard to the cost of such behaviour. It may be advantageous to remove a despot so that a new dominant sow can be established that does not upset the entire social group. But the bottom line is that gated stalls virtually eliminate competition related production losses.