USDA report includes a look at sow housing

According to a special article featured in USDA's Livestock, Dairy and Poultry report, in recent years, a growing number of major U.S. companies that demand and supply pork products have adopted strategies that explicitly move away from direct or indirect use of gestation crates in pork production.

McDonald"s Corp. a major buyer of pork products and thus an indirect user of gestation crates recently announced that it would require its pork suppliers to submit plans by May 2012 that transition suppliers" production facilities from use of gestation crates, to group sow housing. McDonald"s thus joins other major U.S. buyers of pork products1 along with major U.S and Canadian pork-producing companies, in adopting business models that incorporate group sow housing in pork production.2

Pork users and pork producers appear to be making this move in response to a developing public perception that crating sows during gestation is detrimental to the welfare of the animal.

The Current U.S. Hog Production System: Gestation Crates
For the last 30 years, typical U.S. hog production has employed individual crates to house pregnant females during gestation.3 The typical gestation crate measures 7 feet by 2 feet, or 14 square feet, and was adopted by the industry to overcome innate hierarchical swine behavior.

Female swine, in particular, tend toward aggressive behavior to establish dominance when they are housed in groups. This means that freely moving pregnant swine tend to fight until dominance is established. Such aggression can cause serious injury to less-dominant females and to unborn piglets. When the females are crated, aggression and threat of injury are minimized. Gestation crates also facilitate individualized animal care, feeding, and monitoring.

The downside of gestation crates is the severe constraint on movement that the 14- square-foot crate imposes. While the crate affords the pregnant female some limited side-to-side and back-and-forth movement, it totally prevents the animal from turning itself around. The animal welfare questions that are raised by the movement limitations of gestation crates have motivated the industry to adopt a different means of pork production that allows the pregnant animal freedom of movement.

Group Sow Housing as an Alternative to Gestation Crates
A production model based on group sow housing places pregnant swine in open pens that allow them free movement. An accurate description of a "typical" group sow housing barn is elusive because no single type has yet evolved in the United States. Consequently, there is wide variation in design characteristics of existing grouped housing units.

For example, the number of animals grouped in one pen can vary anywhere from 5 animals to more than 100, depending on per-animal space allocations. The groups themselves can be "static," meaning that all the animals in a pen enter it together when the group is formed, or "dynamic," meaning that animals enter and exit the group.

The size of the groups and the per-animal space allocations often determine the method employed to feed the animals.Feeding the animals in a group setting presents serious challenges given the tendency of swine toward aggression, particularly at feeding time.

There are various methods available to feed the animals in a group setting. Three of the most common are electronic sow feeders, where the animals are trained to line up to enter feeding stations from which individualized rations are dispensed, based on information read from chips implanted in the animal"s ear; trickle feeding, where feed is delivered over a period of 15 to 30 minutes to troughs or on the floor of the pen; and free-stall feeding, where the animal enters a stall, often with a door closing upon entry, allowing her protection from aggressive pen mates during feeding.

Each feeding method has a different set of cost, space, and management requirements, which together interact with group size, per animal space allocations, and numerous other physical characteristics of the unit"s design to affect the animals" wellbeing.4

Gestation Crates and Group Sow Housing: What Do Comparative Studies Show?
There are now many comparative studies in the animal science literature that document differences in production performance, behavior, and welfare indications between animals housed in gestation crates and those housed in pens. One of the most often-cited studies was carried out by McGlone et al. (2004).

This study aggregated research findings from 35 previous comparative studies to determine whether sow behavior, performance, or physiology differed between the two housing types. The study tested for statistical differences between farrowing rates; pigs born per litter; oral, nasal, and facial behaviors;5 and cortisol blood levels6 in gestating animals.

The research results, which are summarized in the table below, indicate that the differences between the means of measured variables were not statistically significant. That is, none of measures were significantly (P<0.05) influenced by sow housing type. The study concludes that "gestation stalls or wellmanaged pens generally … produced similar states of welfare for pregnant [females] in terms of physiology, behavior performance, and health."

Summary of 35 Comparative Studies of Gestation Crates and Group Sow Housing

Indicator Measured

Group pen



Is P < 0.05?

Farrowing rate (%)




no, therefore no statistical difference between housing types

Pigs born alive
per litter




no, therefore no statistical difference between housing types

Piglet birth weight (kg.)




no, therefore no statistical difference between housing types

ONF behaviors




no, therefore no statistical difference between housing types

Cortisol ng/ml*




no, therefore no statistical difference between housing types

*nanograms per millilitre

Source: McGlone, adapted from McGlone and Salak-Johnson

This study also addresses two issues important in comparing the different systems. The study indicates that sow productivity as measured by farrowing rates and pigs per litter is not affected by housing type. This is good news to for U.S. pork producers, some of whom equate group housing with lower female productivity and lower asset returns. More important perhaps, the study identifies the producer"s animal handling/management skills as the key to maintaining productivity of sows housed in pens.

With respect to concerns about the effects of gestation crate housing on animal welfare, neither McGlone et al., nor current animal science research generally provide clear, empirical evidence that switching to group housing improves the welfare of pregnant female swine.

The literature is supportive of the contention that sow/gilt welfare is not determined by housing type. "In other words proper design of stalls and pens can result in equivalent animal performance and welfare outcomes, although the design features for achieving that objective will differ. Therefore, it"s not clear that simply switching to group housing will inherently improve or reduce sow performance or welfare."7

The Group Sow Housing Model Often Employs Gestation Crates To Assure Swine Safety
As the sector continues to evaluate sow housing options, it will be important not to overlook two crucial safety features of the group sow housing model: First, the group sow housing model often does not exclude the usage of sow crates.

In current practice in both the European Union and the United States, newly bred sows are crated for around 30 days to insure proper embryo implantation. Moreover, the pregnant females are typically crated for a 5-day period just prior to farrowing. Pregnant females are thus removed from group pens at periods in gestation when they are most vulnerable to aggression and injury.

Second, both production models gestation crate-based and group sow housing move pregnant females into farrowing crates just prior to the birth of the litter.8 The farrowing crate different in dimension and design from the gestation crate is designed to allow the female to position herself to nurse the litter.

The sow"s movement is restricted to prevent injury to the litter, such as crushing or smothering. Crate use in the group sow housing model implies that the female spends about 35 percent of the year 4 months in individual housing and the balance of the year in a group setting.9 Under a gestation crate system of production, the animal is crated 100 percent of the time.

1 In February 2012, McDonald"s Corp. announced that it would require its pork suppliers to submit a plan to transition their hog production facilities to open sow housing operations by May 2012. In March, the Compass Group announced a corporate goal to source pork only from producers using group sow housing "by 2017." In 2011, Wendy"s purchased 10 percent of pork products used in its business from operations that employ group sow housing. Wendy"s is committed to increasing the percentage of pork sourced from open sow housing operations to 20 percent, "over time". Sonic sourced 8 percent of its pork products from open sow housing operations in 2011, with the goal of increasing purchases to 16 percent by 2016. Sonic and Subway give sourcing preference to pork supplied from group housed sow operations. In April 2012, Burger King pledged to purchase pork only from suppliers that can demonstrate documented plans to end their use of gestation crates for breeding pigs. Safeway Inc. and Tim Hortons made similar announcements in May 2012.

2 Smithfield, Hormel, and Maple Leaf Foods stated a commitment to a transition to group sow housing by 2017. Cargill began its transition to group sow housing in 2003. In 2007 it reported that half of companyowned farms had made the transition. In 2009 Cargill reported that half of its contract farms had transitioned to group sow housing.

3 The gestation period for swine is 114 days. A female who has not yet been bred is termed a gilt. A female who has produced a litter (i.e., "farrowed") is termed a sow.

4 See Levis for an exhaustive list. "Gestation Sow Housing Options". National Pork Board. 2007 Sow Housing Forum, SowHousingForum.aspx

5 Oral, nasal, and facial behaviors (such as bar-biting) may include stereotyped repetitive, relatively invariable sequences of behaviors that potentially indicate reduced welfare. (McGlone et al.)

6 Cortisol is a hormone for which elevated levels in animal are an indicator of acute stress. "Cortisol has been the most common physiological parameter used to measure farm animal welfare." (McGlone et al.)

7 Buhr, May 2010 8 Production experiments are currently being carried out in the Netherlands in which farrowing takes place without crates.

9 Assume 2.3 litters/female/year; animal crated for 30 days following breeding, and 5 days prior to farrowing; and farrowing crate for 20 days at farrowing.

McGlone, J.J., et al. 2004. "Compilation of the Scientific Literature Comparing Housing Systems for Gestating Sows and Gilts Using Measures of Physiology, Behavior, Performance, and Health," The Professional Animal Scientist 20 (2004): 105-17.

McGlone, John J., and Janeen Salak-Johnson. 2008. Changing From Sow Gestation Crates to Pens: Problem or Opportunity? presentation at the Manitoba Swine Seminar, Winnepeg, Manitoba, Canada, January 2008.

Buhr, Brian L. 2010. Economic Impact of Transitioning from Gestation Stalls to Group Pen Housing in the U.S. Pork Industry, Staff Paper P10-4, Department of Applied Economics, University of Minnesota, May 2010.



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