Conclusions from a PROHEALTH experimental study
Piglet mortality is a major concern for pig producers. On European farms, approximately one piglet out of five or six is born dead or dies after birth. The main cause of stillbirth is prolonged farrowing possibly due to stress or fatigue of sows; the main causes for post-natal mortality are hypothermia as a result of hypoxia and(or) starvation, crushing by the sow and infections.
There is some evidence that the environment of the sow during pregnancy can generate maternal stress which could influence piglets before and after birth. Notably, in a previous study of the PROHEALTH project, we observed a positive impact of a friendly housing system on sow welfare and piglet survival (see Newsletter No. 2, November 2015). This friendly “enriched” system in which sows were group-housed on deep straw litter and had 3.5 m2 per sow was compared to a system which is a conventional system in many European countries, including France, and in which sows were housed on a slatted floor and had only 2.4 m2 per sow.
The difference in piglet survival likely had its origins during gestation since sows from both systems were transferred, a few days before farrowing, to maternity rooms with similar lactation pens and management practices. Based on these results, we hypothesized that enriching the environment and diet of sows housed in the conventional system to mimic straw supply might reduce maternal stress during pregnancy and piglet mortality.
Three experimental systems were thus compared during pregnancy, from the less to the more enriched: the conventional system (C, on a slatted floor); the conventional system which was enriched with manipulable material and straw pellets (CE), and the enriched system (E, on deep straw litter and with additional space per sow). In the CE system, pieces of oak attached to a chain were provided to sows to fulfil their need for investigatory behaviour and straw pellets were provided to reduce their frustrated feeding motivation. Straw pellets were provided in the trough after each meal from 3 to 104 days of gestation. Then, all sows (n = 83) were transferred into farrowing pens and housed in identical individual crates on a slatted floor.
Maternal stress was assessed by cortisol concentrations in saliva and by behavioural traits. During late pregnancy, cortisol concentration of sows was greater in the conventional system (C) than in the enriched system (E) and was intermediate in the conventional enriched system (CE). The enrichment reduced sow stereotypies, which are repetitive movements or postures illustrating frustration (ECE>C). Piglet mortality during farrowing and within 12 h of birth was lower in the two enriched systems than in the conventional one. Total mortality (i.e. live-born + stillborn deaths) was lower by 4 percent points in these 2 systems but the difference did not reach the level of significance.
To conclude, when sows were housed in a conventional intensive system during pregnancy, enriching their environment with manipulable material and their diet with straw pellets throughout gestation improved their welfare. These effects were accompanied by a reduction in piglet neonatal mortality. Improving sows’ welfare during gestation should therefore be considered to reduce piglet mortality in pig farms.