Topping the list of criticisms involving today’s swine-production technology is the use of gestation-sow crates. Most important among the alleged faults:

(1) In a straight-side crate, a sow cannot turn around or walk (allegedly depriving her of strong behavioral needs).

(2) Residing in a crate causes stereotypic behaviors such as bar-biting and waterer-pressing (which allegedly indicate emotional stress).

Animal activists believe an individual straight crate is an inhumane place for dry sows and demand they be kept in groups in paddocks, pastures or pens.

But many scientific authorities consider the crate to be an optimal accommodation in an imperfect world, a compromise that evolved rationally. (See articles by Curtis, Levis, Salak-Johnson, among others, in proceedings of the 2007 Sow Housing Forum at the National Pork Board Web site.)

Role of Scientific Evidence

Most producers, now accustomed to and outfitted to keep sows in crates, want to know why they should remodel facilities and change husbandry systems to keep sows in groups.  Does scientific evidence on sow well-being show the need for such major changes? If not, then regardless of what activists demand, it makes no sense to switch to a group paradigm. In fact, it might not even be in the sows’ best interests.

Decisions on gestation systems should be science-based and, therefore, most likely to be sustainable and profitable.

Of course, producers should listen to critics, try to understand their concerns and deal with consumers in accordance with a reasonable social contract. But they should heed activists’ demands if, and only if, doing so actually would improve sow well-being.

Simply put, reviews and meta-analyses of the scientific literature indicate that a sow would not be generally better off kept in a group than residing in a well-designed and well-managed crate.

Needs are central to determining the gestation crate’s humaneness. Does a sow need to turn around?  Does it need to walk?  If so, how strong are those needs? 

Behavioral Needs

One theory of behavioral causation (formulated by ethologist Barry Hughes) involves whether a behavior is stimulated externally or internally, by the surroundings or by the body.

If a behavior occurs spontaneously wherever the animal is, then the behavior apparently does not require a specific environmental stimulus — it is internally motivated, and should be considered as a possible need of some strength or another.

If it is a strong need, then the environment should allow the sow to express that behavior. Otherwise, when a sow is motivated to perform the behavior but is constrained by its environment, the sow will become frustrated, which can have consequences for animal health, productivity and, presumably (based on alleged behavioral indicators), for the animal’s feelings.

Scientific Research

Some years ago, University of Illinois animal scientists (see footnote) reported on two experiments on turning and walking behaviors of mated gilts in two different experimental crate settings.

In the first experiment, gilts ranged from 244 pounds to 312 pounds and the head-crown-to-tail-base length was 52 inches to 58 inches. Crates were arranged to study two gilts at the same time. The crates were 7 feet long; flared at one end, pointed at the other; and either 22 inches or 24 inches wide at the center. (See Figure 1.)

Gilts could completely turn around in the flared end of either crate. The feeder and waterer were placed at one end of the crate, in all four possible location combinations. The crates were surrounded by a high screen, so the gilt had no sense of direction within the larger environment.

Here’s what the study found:

  • On average, a gilt turned ~11 times a day.
  • Neither the feeder nor waterer location affected the gilt’s turning frequency. Turning by a bred gilt apparently is internally motivated ­— it is a behavior that might need to be accommodated by the environment’s design. Most turns were not stimulated by any obvious external feature. Gilts turned nearly as often regardless of where the feed and water were located.
  • Narrowing a crate from 24 inches to 22 inches considerably reduced daily turning frequency, down from ~13 to ~9. Although a gilt was able to turn in a crate of either width, the increased difficulty of turning in the narrower crate seemed to reduce the desire to turn. This indicates that if a bred gilt has a behavioral need to turn, it is relatively weak. When it required more exertion, the gilt sometimes chose to forego the stimulus.

In the second experiment, the gilts’ weight ranged from 279 pounds to 383 pounds and body length was 51 inches to 59 inches. Crates were either 7 feet or 11 feet long, and both ends were either flared (48 inches) or rectangular, in all four possible permutations. All crates were 24 inches wide at the center. (See Figure 2.)

A gilt could move her whole body in two ways — turning (in the flared crates) or walking (forward and backward). If gilts turn simply for exercise, then walking might be substituted for turning in the longer crates, and turning frequency might decline.

Here’s what the study found.

  • Crate design did not affect the distance a gilt walked (average of 430 feet per day). Incidentally, sows walk mainly to access vital resources. Sows outdoors reportedly walk 6,500 feet or more daily; sows in indoor pens walk ~650 feet.
  • Gilts in longer, flared crates did not substitute walking for turning.

So what did we conclude?

  • Turning did not seem to be motivated by a strong need to face or orient the body in a specific way.
  • Turning did not seem to be motivated by a strong need to move in general or for physical exercise.
  • For a bred gilt, turning may be a needed behavior, but science showed it’s a weak need.
  • A bred gilt walks little, if at all, more than is necessary to access vital resources and accommodate maintenance behaviors (defecation and urination).

Given that, the implications are:

  • Because a gilt does not appear to have a strong need to turn or walk, a standard 7-foot x 2-foot straight-side crate should not be faulted as inhumane because a sow cannot turn around or walk.
  • For these and other reasons, industry leaders should work to educate the public about the standard gestation crate’s humaneness.

So what’s next? In the September column, I will further explore the humaneness of individual crates for gestating sows.

Editor’s note: The study referenced is J. M. McFarlane, K. E. Bøe, S. E. Curtis.  1988. “Turning and walking by gilts in modified gestation crates”; Journal of Animal Science 88:326-333.