Hygienic aspects of silage made on grass contaminated with Iberian Slug (Arion lusitanicus) and Grey Garden Slug

-This study aimed to clarify whether contamination of invasive Arion vulgaris slugs into grass crop might reduce the silage quality and increase the risk for certain animal diseases.. The last decades, A. vulgaris has caused severe damage of garden plants, vegetables and berries in northern Europe. Moreover, Norwegian and Swedish farmers have expressed their concern experiencing heavy slug invasions of meadows for silage production. Reduced palatability combined with nonspecific health symptoms in ruminants has been suspected, but not proven, to be caused by feeding of slug-contaminated silage. This is, to my knowledge, the first study documenting that contamination of adult A. vulgaris slugs into grass crops severely reduces the silage quality, probably because the high protein and water content in the slugs disturb silage fermentation. The conclusion is based on chemical and microbiological analyses of silage quality in a controlled ensiling experiment, where grass crops was added different silage additives and slug levels. Increased slug amounts gave increased quality-loss in silage. Through a prevalence study and laboratory experiments where A. vulgaris was fed Listeria monocytogenes and Clostridium botulinum type C, it was showed that slugs have a vector potential for pathogenic bacteria. L. monocytogenes, causing the diseases listeriosis, is common in the environment. As inadequate ensiling conditions can enrich these bacteria, listeriosis is frequently associated with feeding of poor quality silage in ruminants. The prevalence study showed that A. vulgaris commonly carry L. monocytogenes both internally and externally. Multilocus sequence typing of L. monocytogenes strains isolated from slugs, showed many sequence types with known potential to cause disease in ruminants as well as in humans. Botulism is a severe animal disease which can be caused by carcass-contaminated silage, but fortunately there was no indication that A. vulgaris can stimulate C. botulinum type C enrichment. Despite disturbed fermentation with increased pH in slug-contaminated silage, strictly anaerobic ensiling conditions sufficiently prevented L. monocytogenes enrichment. However, Clostridium tyrobutyricum enrichment was strongly stimulated by slugs. Since silage is a known contamination source to milk, such silage may increase the risk of production losses due to ?late blowing? of semi-hard cheese. The use of silage additives based on acids and chemicals during ensiling of slug-contaminated grass crop effectively improved silage fermentation, even in severely contaminated crops. Consequently, such additives may ensure silage of acceptable fermentation quality and good feed safety. However, the use of lactic acid bacteria inoculation and wilting as preventive measures had not sufficient effect. Although no pathogens affecting animal or human health were detected in slug-contaminated silage, this study shows that slug-contaminated silage may affect animal production and feed intake through reduced feed quality. To ensure high feed quality, the use of additives based on acids or other chemicals is strongly recommended for ensiling of grass crops contaminated by slugs.

Under the latest years, slugs have been recognised as a pest not only in gardens but also in pasture-land and meadows for roughage production. Especially in the western parts of Norway, the meadows has been invaded by slugs to a extent that has resulted i n rejection of feed lots. It has also been suspect of relations between animal health problems and silage contaminated with slugs, and questions concerning the risks for botulism and other animal diseases connected to slugs mixed in the forage has been ra ised. The same problems are currently faced in Sweden (C. Hultén, personal communication). Unfortunately, to our knowledge, no scientific reports on this topic are available and studies are thus requested from farmers, veterinarians, agricultural advisers and authorities. The principal objective of this study is thus to investigate if occurrence of slugs in silage may influence the hygienic feed quality negatively and if the prevalence of pathogenic bacteria as Clostridium botulinum and Listeria or moulds may be increased in such feed.