Consumers have been driving the conversion of sow farms toward the use of group housing for sows. The swine industry has been hesitant to adopt this practice due to concerns over sow aggression and lack of control over individual feed intake in some group housing systems.

This study compared the effects of three mixing strategies on sow performance in fully-slatted group pens, with sows fed daily in free-access stalls. A total of 252 sows were studied over six replicates, in groups of 14 sows per pen. The treatments consisted of: 1. Early mixing (EM) — sows mixed into groups at weaning; 2. Late mixing (LM) — sows stall-housed at weaning and mixed at five weeks gestation; and 3. Pre-socialization (PS) — sows mixed for two days after weaning, then stall housed for breeding and up to five-weeks gestation, after which they were mixed (same groups).

The study took place at the Prairie Swine Centre’s research farm, a 350-sow farrow-to-finish unit located in Saskatchewan, Canada.

This group system allows individual feeding of sows in stalls, and in this experiment, once the sows were fed in the morning they were locked out of the stalls in the communal loafing area for the rest of the day. All sows were fed a commercial dry-sow ration appropriate to their needs following standard commercial practice. Water was provided by a single nipple drinker per stall for access during feeding, and also a water nipple added at one side of the communal loafing area.

Sows were bred on a weekly basis, with 14 sows bred per week, resulting in one gestation pen being filled every two weeks. To remove effects of room, all sows were housed in one gestation room from the time of weaning, with the free-access stalls used as breeding stalls. Piglets were weaned at 28 days of age.

Measurements

Researchers recorded sow reproductive measures such as wean-to-standing heat interval, conception rate to the first or second service, total pigs born (alive, mummified, stillborn), pigs weaned and weaning weight. Sows culled during the trial and the reasons (reproductive failure, lameness and other) were also recorded.

Individual body weight, back fat depth and body condition score were recorded on all sows at weaning, five weeks after mating and before moving to farrowing. BCS was measured according to Coffey et al, and back fat thickness was measured by an ultrasonic scanner by a trained technician.

Sow behavior in all pens was recorded by video camera to record aggression at mixing. A camera was suspended over each pen, and set to record from 9 a.m. to 4 p.m. for two days, starting on the day of mixing. Prior to mixing, all sows were individually identified with spray markings on their backs for clear identification.

Footage was transcribed in real time by trained observers who were blind to treatment, and the total number and duration of aggressive bouts was recorded. Through the individual identification of sows, the number of times over the two days of footage that each individual participated in an aggressive encounter was recorded.

Results showed that the EM treatment had the highest conception rate (98%), followed by PS treatment (94%) with the LM treatment having the lowest conception rate (87%). This may reflect suboptimal stimulation of estrus in stall housing (LM). In contrast, the EM and PS groups received mixing stress immediately at weaning, which may have stimulated clearer estrus expression. The EM treatment also showed a significant reduction in the number of stillborn piglets. There were no other differences in production performance among the treatments. Cortisol levels and aggression at mixing were also measured, with no significant treatment differences found.

For producers, this means that a variety of mixing options can be used successfully for sows in group housing, depending on the herd size and management preferences. In addition, if welfare regulations limit the amount of time that stalls can be used, producers can adopt shorter periods of stall use (e.g., for insemination) without compromising production. Many producers are now adopting the practice of mixing shortly after insemination (i.e., mixing within approximately three to four days after breeding). This practice results in efficient use of barn space and requires fewer stalls than the alternative of stalling sows until implantation is complete (approximately four weeks after insemination). For producers converting existing stall barns to group housing, the option of moving to earlier grouping times can reduce space requirements and help to maintain herd size following conversion. 

Researchers: Jennifer Brown, Prairie Swine Centre Inc., Saskatoon, Canada; Yolande Seddon, University of Saskatchewan, Saskatoon; and Yuzhi Li, University of Minnesota, Morris.