Christine Pelland from South West Ontario Veterinary Services, Genetic Selection For Reduced Aggression In Lactating Sows

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Some animal welfare advocates argue that the permanent confinement of sows in farrowing crates will limit the sow’s freedom of movement and the ability to show typical species appropriate behaviour. They further argue that permanent confinement increases the risk for skin lesions and udder injuries. On the other hand it has commonly been argued that loose housed sows are at greater risk of crushing their piglets. Recent research, however, has repeatedly demonstrated that short-term restraint of sows in the first few days after farrowing can lead to a significant reduction in piglet crushing  in comparison to farrowing pens with no confinement period. An argument for confinement is that farm staff can be at increased risk of injury due to aggression by sows that are not confined. In some European countries such as Norway, Sweden and Switzerland, farrowing crates have already been banned. In Germany, sows may only be restrained for 5 days in farms with new and converted farrowing pens. More attention is being focused on work place safety for stockpersons that are caring for sows and piglets that are not in confinement. These German researchers wanted to develop tests that would reveal the behaviour of lactating sows in loose housed farrowing environments. Sow behaviour towards humans was evaluated during different daily routines. The study was conducted in a nucleus herd with 771 purebred Landrace sows. Data were collected from October 2016 until December 2018. Sows were kept in individual indoor pens with movable farrowing crates in which the sows were restrained from 7 days before to an average of 7 days after farrowing.

The Dummy Arm Test (DAT; 1444 observations) was used to assess the sows’ reaction towards a stockperson handling the piglets around day 4 after farrowing. The Towel Test (TT; 2846 observations), measured the reaction of sows to a novel object in an unexpected situation. The Trough Cleaning Test (TCT; 2805 observations) described the sows’ response to common procedures such as trough cleaning. TT and TCT were conducted on days 3 pp (closed crates) and 10 pp (open crates).

The researchers found the following:

  • Most sows showed no or only a slight reaction to human interactions and did not attempt to attack. However, a strong defensive reaction of sows was recorded in 4.0% (TCT), 4.5% (TT), and 10.7% (DAT) of observations. ( These levels of aggression were somewhat higher than previous studies that reported aggressive behaviour as low as 0.9% of interactions. )
  • The level of aggression of sows to human interactions was higher in the open pen system on day 10 post farrowing than in farrowing crates on day 3 post farrowing
  • Estimates of heritabilities (h2 ± SE) were h2 = 0.17 ± 0.05 for behaviour of sows towards humans (DAT), h2 = 0.19 ± 0.04 for response of sows towards unexpected situations (TT), and h2 = 0.13 ± 0.04 for reactions of animals to TCT. ( The authors suggest that these estimated heritabilities provide sufficient genetic variation for the selection of less aggressive animals with benefits for both human safety and animal welfare)
  • Genetic correlations (rg ± SE) ranged from rg = 0.59 ± 0.37 between TT and TCT to rg = 0.77 ± 0.30 between TT and DAT. ( Sows that were aggressive in one type of aggression test were more likely to show aggression in other tests. )

Take Home Messages:

  • The Dummy Arm Test, Trough Cleaning Test and Towel Tests appear to be suitable for assessing the aggressive behaviour of sows towards humans.
  • Behavioural traits derived from these tests could be used as new phenotypes for the genetic selection of less aggressive sows.
  • Because most sows in this study showed few defensive reactions to human interactions, the level of aggressive behaviour might be considered by some to be too infrequent to merit efforts towards genetic selection for lower aggression towards farm staff. If, on the other hand, you are a caring stockperson that is the target of occasional aggression by sows your view point is likely to be much different.

Ref: J Kecman , J Neu 2, N Göres, B Voß , F Rosner , N Kemper , H H Swalve   Genetic aspects for the behaviour of lactating sows towards humans Animal . 2022 Jun 13;16(7):100559. doi: 10.1016/j.animal.2022.100559. Online ahead of print.