Grass silage for growing-finishing pigs in addition to straw bedding: Effects on behaviour and gastric health

Summary

In organic and other enriched housing systems, straw is commonly used as enrichment material for pigs. Its positive effects on health and behavioural welfare are well known. However, potential additional impacts of roughages (other than straw) have rarely been investigated. On six organic farms, we therefore investigated how providing grass silage affects behaviour, gastric health and performance of growing-finishing pigs. Per farm, two to four pens were included in the experiment, with group sizes ranging from five to 26 pigs (total n = 368), and stocking density ranging from 1.65 to 3.50 m2 per pig during finishing. Groups were provided with either grass silage (SIL) or straw (CON) in a rack. Long-stack straw was used as bedding material in all pens. Skin and tail lesions and tear staining were assessed four times throughout the fattening period, and behavioural observations were conducted three times. After slaughtering, pathological damages in the gastric mucosa were scored (score 0–6). Slaughter weight, lean meat proportion and proportion of polyunsaturated fatty acids in body fat were obtained. Data were analysed using linear mixed effect models and parametric bootstrap. Providing grass silage did not alter pen-mate directed manipulations (P > 0.1). Prevalence of tail lesions was too low to confirm numerical differences statistically (0.2% of all assessments in SIL vs 2.6% in CON). Pigs with access to grass silage were occupied longer with substrate (silage or straw) than CON pigs (P = 0.01). The prevalence of slight to severe damages in the gastric mucosa was not affected by treatment (score 0 vs. 1–6; P > 0.1). However, among those pigs that had damages at all, severe damages including gastric ulcers were less frequent in pigs provided with grass silage (score 1–4 vs. 5–6; P = 0.03). The overall prevalence of gastric ulcers (score 6) was 0.7% of all pigs in SIL and 6.1% in CON groups. No impact of grass silage provision was found for slaughter weight, lean meat proportion and body fat quality parameters. In conclusion, our results demonstrate that grass silage is an appropriate feed and enrichment material to stimulate species-specific foraging behaviour and to reduce the development of gastric ulcers.