Grouping of sows after weaning in a mixing pen did not reduce the level of lameness

According to Danish regulations gilts and sows must be housed in groups from weaning until 7 days before expected farrowing. Mixing sows both after weaning and after mating may/will impair reproduction results and increase prevalence of lameness. A Danish study shows that approximately 90 % of medical treatments in gestation are attributed to lameness.

The aim of the current study was to reduce the frequency of gilts and sows being treated for lameness in the period from weaning until three weeks after mixing in the gestation pen.

A total of 2350 gilts and sows in two herds were included in the study. In both herds, sows were weaned into a mating pen with an activity area with straw bedding and one free access stall per sow. At weaning sows were assigned to a control group were they had free access to the feeding stalls from weaning until transfer to the gestation unit and a test group where the sows were pre-mixed in the mating pen before transfer to the gestation unit. Mixing was done by refusing access to the stalls in brief periods of time. During mixing, the area per sow was 1.8 m² and 3.5 m² in herd 1 and 2, respectively. In the gestation unit gilt and sows were housed in stable groups and fed either in electronic sow feeding stations (herd 1) or long trough (herd 2).

The mixing strategies differed between herds. In herd 1, the transfer of sows into the gestation unit was done after insemination, whereas sows stayed in the mating pen for 4 weeks in herd 2 before transfer to the gestation unit. The sows were assessed for lameness in the gestation unit at week 0, 1, 2 and 3 on a scale of 1 to 4. Lameness was scored on a scale from 0 (healthy) to 4 (immobile).

Lameness was analysed using logistic regression in SAS, proc glimmixed, with group and weeks after mixing as fixed factors and batch*pen as random factor.

In herd 1, the number of treated sows was significantly higher in the trial group compared to the control group (p=0.0277). There was no significant difference between the two groups in herd 2. Thus, mixing of sows under optimal conditions in the insemination unit did not have the expected effect. Possible explanations could be the smaller area per sow during mixing in herd 1, or the fact that the sows in herd 2 were loose in four weeks before premixing in the mating pen. This is consistent with the treatment results, and indicates that the sows in herd 2 used the prolonged period of time in the insemination unit to complete establishment of the hierarchy.

In conclusion, the strategy where gilts and sows were weaned into a specially designed pen and pre-mixed failed to reduce the frequency of lame gilts and sows in the gestation unit.

Disclosure of Interest: None Declared.