The variation in body size of sows needs greater consideration before gestation stalls are abandoned altogether.
Pork producers should ask themselves whether stalls could be designed to fit the sows' body sizes better, states John Deen, DVM, at the University of Minnesota's Department of Veterinary Population Medicine, as he reports on a project funded by Minnesota Pork Checkoff.
Deen analyzed two stall treatments at the University of Minnesota Southern Research and Outreach Center in Waseca, MN:
Small sows were allocated to stalls measuring 24 in. wide; large sows were placed in stalls 26 in. wide.
Sows were allocated to stalls based on their height, where the width of the stalls had to be at least 75% of the highest point of their back, above the last rib.
This method of predicting the space requirements for sows of different sizes is called morphometry, where different body measurements are used to predict how different body sizes will fit in a three-dimensional shape. (See Table 1). The length of the stall was fixed at 80 in.
“Previous studies have shown there is a measurable benefit to added (stall) width in terms of reduction of injuries and ease of getting up, although differences in mortality and productivity levels have not been seen,” Deen reports.
“Allocation of a minimum stall width is problematic, as the heights of sows vary widely, and their distributions are unequal from weaning group to weaning group,” he adds. “To meet the 95th percentile of requirements, it is calculated that the stalls should be at least 28 in., center-to-center.”
That leaves two choices — provide adjustable stalls or provide a range of stall widths that meet the range of requirements established using the sow height requirement.
Using a research model, Deen took into account the variation in width requirements and sow sizes, then he determined the average stall width should be approximately 25.6 in., a 6.7% increase in width to meet the requirements of the sample herd. The range then would be from 22 to 28 in., at 2-in. increments.
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“There would be a little increase in feed and water equipment costs, front and back gate costs, along with increased floor space,” he says. “We estimate that the additional cost would be approximately 5% for new construction. For renovations, this may be problematic, if it is done without reducing herd size.”
Attempting to match newly weaned sows with the appropriate stall widths — 22, 24, 26 and 28 in. — would make it very difficult to keep breeding groups in the same row, however. The alternative would be to place four sizes of stalls in four distinct areas of the gestation barn.
Sows are least comfortable and at greatest risk of injury when space requirements aren't met.
Sows normally do not injure their backs because the stall isn't high enough, Deen explains. Rather, inadequate width of the stall relative to the sow's height forces her to press her back against the side of the stall while lying down.
Complicating matters further, if her legs extend into the adjoining stall, chances are greater that her neighbor will step on and injure her legs. A newly weaned sow's underline should not extend into the adjoining stall for the same reason.
“Increasing the stall dimensions in relation to sow dimensions will increase the dynamic space available to the sow to move more freely,” Deen says. “Stall length and width relative to the animal's length and breadth are the two critical parameters affecting duration of posture, frequency of postural change and time taken for postural change. The research literature shows that as sows progress from mid- to late-gestation, they take longer to shift from a sitting to a lying position when stall size is inadequate.”
The morphometric measurements for modern sows in the United States over multiple parities and days of gestation (Table 1) were compiled through the work of John McGlone at Texas Tech University.
“Most commercial gestation stalls, averaging 23 × 84 in. in the McGlone study, are not wide enough to contain the sow when lying down,” Deen observes.
At the Prairie Swine Centre, Y.Z. Li and Harold Gonyou studied the behavior and udder extension into adjacent stalls when lying down. They found a 21.7-in. wide stall is suitable for gilts and small sows (441 lb.), a 23.6-in. wide stall for medium-sized sows (441-507 lb.), and a 25.6-in. wide stall is needed for large sows (507 lb. and higher) during the first month of gestation.
However, by the 14th week of gestation, gilts and small sows should be housed in 25.6-in. wide stalls, while the medium-sized and large sows need 27.6-in. wide stalls.
Research in New Zealand by J.L. Barnett and G.M. Cronin contradicted the Li-Gonyou findings, noting sows favored the narrower stall widths, 23.6 in., based on sow behavior, stress hormone levels and immunological response of the sows. “They observed that in the wider stalls (29.5 in.), sows spent more time standing and less time lying down,” Deen notes.
Earlier work at the Prairie Swine Centre evaluated gilt behavior when housed in stalls or pens during gestation and farrowing/lactation. Stalls/crates were classified as narrow (16.7 in.) or wide (31.5 in.), and the pen was 7.9 sq. ft.
“The widened farrowing crate following pen gestation appeared to be less comfortable than either the narrow crate or the farrowing pen,” researchers reported.
The consensus, then, is there is no consensus regarding the optimum width of the gestation stall, says Deen, noting more work must be done if producers wish to make a case for preserving individual gestation stalls for sows.