Two different strategies for housing gilts after mating did not affect the proportion of gilts culled

Gilts and young sows often have the lowest rank in a group of sows mainly because rank to a certain extent is defined by bodyweight (Hoy et al. 2009). It is often difficult for animals with low social status to access the electronic sow feeder because they are feed later than sows with a higher status and tend to be displaced from the feeder queue more often. Sows with low social status were also observed less often in the lying area (O’Connell et al. 2003). At the same time, gilts and young sows are at risk of being culled from the herd before their economic potential is fully exploited (Anil et al. 2005). The aim of this study was to compare two different strategies for housing gilts after mating on the proportion of gilts culled throughout the first gestation and lactation period. The two strategies were: mated gilts in dynamic groups with gilts mated in the previous weeks versus mated gilts in stable groups with sows.

A total of 1355 gilts (Landrace × Yorkshire) in two different herds with group housing and electronic sow feeding were included in the study. Both herds had approximately 1100 sows. The gilts were on average 275 days old when they were introduced to either a dynamic groups with gilts mated in the previous weeks or stable groups with sows. In both herds the gilts were introduced to the pen in groups of 12–15 gilts at 4 weeks after mating. All gilts were trained in using the feeding station before mating. The total area per gilt was the same in both herds and pen types (1.7–1.9 m² per gilt).

Data was collected on farm by a technician from the Danish Pig Research Centre (PRC). On three occasions all gilts were inspected for lameness; just before mating, two weeks after grouping in the gestations unit, and just before moving to the farrowing unit. Lameness was assessed using the following scale: no lameness, slightly lame, severely lame and not able to stand. Each week at 9 am a scan of the pens was made and it was recorded if the gilts were resting in the lying area or in the activity area. The proportion of gilts culled throughout the first gestation and lactation period was collected. Further, the individual feed intake was measured by collecting data from the feeding stations (Skiold Datamix).

The proportion of gilts culled throughout the first gestation and lactation period and the proportion of gilts with lameness was analysed using a Fisher’s Exact Test. Lying behaviour and individual feed intake was analysed by mixed-model (SAS^®; USA) with weeks in the pen, number of gilts in the pen and group as fixed factors and pen as random factor. The herds were analysed separately.

There was no significant difference regarding the proportion of gilts culled throughout the first gestation and lactation period (Table 1). Also there was no significant difference regarding the proportion of gilts with lameness between the two housing strategies (herd 1: P = 0.62; herd 2: P = 0.18). Further, the strategies did not show any significant differences in regard to feed intake (herd 1: P = 0.90; herd 2: P = 0.14).

Table 1.  Proportion of gilts culled throughout the first gestation and lactation period (%)

In both herds the proportion of gilts in stable groups lying in the activity area was higher compared with gilts in dynamic groups (P < 0.001). The explanation for this finding could be that the pens with stable groups were smaller and had fewer “lying nests” than the pens with dynamic groups. In conclusion, group composition did not influence either the proportion of gilts culled, lameness or feed intake. A further effort to reduce the proportion of culled gilts is needed and it could be relevant to focus on socialisation on young gilts, pen design and new strategies for mixing gilts and sows.