When sows are mixed in large groups there can be a significant amount of aggression between sows as social hierarchies are established. This aggression can lead to traumatic injuries and consequently there are welfare and economic concerns. For many years, some producers have intuitively been providing additional floor space for sows when they are mixed. These Australian researchers wanted to examine the effects of floor space on the amount of aggression and stress. Aggression and stress were measured during the period from mixing until 27 days after insemination with 6 different space allowances that ranged from 1.45-2.9 m/sow as the variable. Sows were introduced to treatments within 4 days of insemination. Sows were floor fed 4 times per day (2.5 kg/sow per day). Similar-sized pens but with varying groups sizes of 10 to 20 sows were used to create the various stocking densities. Space treatments were appropriately randomized to pens. Although it may be argued that space allowance is confounded with group size in this design, there was no evidence in previous experiments of group size effects, for pens of 10 to 80 sows, or appreciable interactions between space and group size on aggression, stress, and reproduction.
The researchers found that there was a consistent linear effect of floor space allowance on aggression at feeding at Day 2 ( < 0.0001) and plasma cortisol concentrations (as a measure of stress) at Day 2 ( = 0.0003), with aggression and stress declining with increasing space. However, there were no effects of space allowance on aggression and stress at Day 26 (= 0.14 and = 0.79, respectively). These results show that increased floor space in the immediate post-mixing period reduces aggression and stress and that sows may adapt to reduced floor space over time.
Ref: Hemsworth PH, Morrison RS, Tilbrook AJ, Butler KL, Rice M, Moeller SJ. Effects of varying floor space on aggressive behavior and cortisol concentrations in group-housed sows. J Anim Sci. 2016 Nov; 94(11):4809-4818. doi: 10.2527/jas.2016-0583
Take Home Messages:
- Providing increased space immediately after mixing can reduce aggression and stress in sows that are being mixed.
- The need for this additional floor space appears to decline over time. Presumably once the social hierarchy is established there is less need for the extra space.
- It is nice to see the scientific evidence confirming producer intuition and observation.
Submitted by Brent Jones, DVM