The provision of lucerne to sows evoked greater arousal in response to an anticipatory behaviour test

Environmental enrichment is thought to be beneficial for pigs. Exposure to enrichment develops resilience to future stressful events by exposing animals to mildly stressful experiences leading to adaptation (Crofton et al. 2015). Rodents housed in enriched environments had greater corticosterone concentrations (Benaroya-Milshtein et al. 2004) and grower pigs housed in enriched environments had greater salivary concentrations of cortisol (de Groot et al. 2000). We investigated the effect of providing lucerne to sows before parturition, on their anticipatory response to the introduction of a feed cart and of a feeding event. We hypothesised that sows provided with lucerne would produce greater concentrations of cortisol and would perform more postural changes than sows that were not provided with lucerne.

Large White x Landrace sows were loaded into conventional farrowing crates approximately 7 days before parturition. Sows in the lucerne treatment were provided with 1 kg of lucerne hay daily, and sows in the control treatment had no lucerne hay. Sows were fed manually twice daily from a feed cart at 7 a.m. and 3 p.m. After 3 days in the farrowing crate sows were subjected to an anticipatory behaviour test. On the day of the test blood was collected via an indwelling ear vein catheter every 15 min for 60 min before, and 60 min after, the introduction of the feed cart and feeding event. Behaviours were recorded via video for analysis. At 3 p.m. (normal feeding time) the feed cart was moved into the room and left for 3 min. After 3 min the sows were given their daily feed ration. For behavioural analysis there were n = 10 control sows and n = 11 lucerne sows. For cortisol analysis there were n = 11 lucerne sows and n = 9 control sows. Plasma was assayed for cortisol using a radioimmunoassay (MP Biomedicals LLC, Santa Ana, CA, USA). Cortisol data were analysed using a repeated-measures analysis of variance and behavioural data with a general linear model in SPSS v24.0 (IBM, Armonk, NY, USA). Data that were not normally distributed were log₁₀ transformed before analysis and all data are presented as back transformed means. The concentration of plasma cortisol was significantly greater for the sows receiving lucerne (Fig. 1) compared to sows that did not receive lucerne (P < 0.05). This effect was only seen after the introduction of the feed cart, therefore, the provision of lucerne altered the cortisol response of the animals to the feeding event. Sows that received lucerne displayed a greater number of behavioural transitions than the sows that did not receive lucerne (P < 0.05).

Our data suggest that sows provided with lucerne display greater levels of arousal in anticipation of the arrival of a feed cart and a feeding event, both in terms on hypothalamic-pituitary-adrenal axis and behavioural activity. This is in keeping with previous reports on the effects of enrichment. Therefore, our data indicate that lucerne may be an effective enrichment for sows before farrowing.

Fig. 1.  The mean plasma concentration of cortisol (ng/ml) for sows for 60 min before, and 60 min after, the introduction of a feed cart. Arrow indicates the introduction of the feed cart.