Effects of gestational olfactory enrichment on adaptation to weaning in pigs

International audience

English. In conventional farms, the use of odours to enrich the environment, which is often poor and monotonous, may offer a simple and cost-effective strategy to enhance welfare of pigs. Furthermore, pigs are capable of prenatal olfactory learning, which is context-dependent and can have longlasting behavioural effects upon odour recall. We aimed to evaluate whether the recall of an odour perceived in a positive context during prenatal life would promote better adaptation to weaning in piglets. Fifty-four gestating sows and their piglets were used in three replicates. In each replicate, enriched sows (n=9) had access to an enriched room 3 times/week for 2h throughout gestation. The room was odourised with anise and contained a peat box, straw bedding, and odourised objects, with music or nature sounds playing continuously in the background. Each visit was paired with the voluntary ingestion of aniseed sugar cubes (525 mg of anethol/intake). Control sows (n=9) were continuously kept in their barren pen. At weaning (D28), piglets from each prenatal treatment were allocated to an anise-odourised or control non-odourised room, resulting in 4 prenatal x post-weaning treatments (n=12 pens of 4 piglets/treatment). Piglet behaviour was recorded using 5-min scan sampling for 6h/day on D28 and D29. On D25 and D29, blood cortisol and blood cell counts were measured. Feed refusals and piglets were weighted on D29, D35 and D42. Effects of prenatal treatment, post-weaning treatment, day and their interactions were analyzed using linear mixed-effect models in R. Prenatal treatment did not affect post-weaning weight gain, but compared to piglets from control sows, piglets from enriched sows ate more in the first 24h post-weaning (D29, p<0.05). On D28 and D29, they also spent more time at the feeder (p=0.004), less time exploring the enrichment materials (p=0.006) and tended to spend more time resting (p=0.06). In the odourised post-weaning room, piglets prenatally exposed to the odour spent less time displaying undesirable social behaviours than non-exposed piglets (prenatal x post-weaning treatment, p=0.04). Compared to male piglets from control sows, male piglets from enriched sows had lower blood cortisol concentrations (prenatal treatment x sex, p=0.007), and tended to have a lower neutrophil/lymphocyte ratio (prenatal treatment x sex, p=0.05) on D25 and D29. While the effects of odour recall in the post-weaning environment were limited, providing gestating sows with regular access to an enriched environment positively affected the stress-related behavioural and physiological responses of their piglets at weaning.