Free-range laying hens at risk for skin disease
medwireNews: Study results from Sweden indicate that free-range laying hens are at greater risk for acquiring Erysipelothrix rhusiopathiae than those housed in conventional or furnished cages.
"Considering these results, the prophylactic measures may have to diverge between housing systems and vaccination is one way to prevent erysipelas in flocks at risk," say Helena Eriksson (National Veterinary Institute, Uppsala) and colleagues in Veterinary Record.
The team examined associations between housing systems - categorized as cage systems (conventional and furnished with perches and dust baths), indoor litter-based systems, and free-range systems - and E. rhusiopathiae occurrence using data for all laying hen flocks found with the bacterium between 1998 and 2011.
During the study period, erysipelas was discovered in 51 flocks, report Eriksson et al. Of these, 22 were from 15 farms with indoor litter-based systems, and 29 flocks were from 21 free-range farms. Notably, no cases came from flocks at farms using cage systems.
The team also analyzed serum samples from 129 flocks, of which 40 were from furnished-cage systems, 39 from indoor litter-based systems, and 50 free-range. Serologic testing for the presence of antibodies to E. rhusiopathiae showed that mean flock absorbance values from the free-range flocks in this subsample were significantly higher than the corresponding values from other housing systems. Specifically, the mean absorbance values were 0.76 and 0.75 for flocks housed in furnished cages and indoor litter-based systems, compared with 0.88 for free-range flocks.
While the transmission and pathogenesis of E. rhusiopathiae in laying hen flocks has not yet been clearly defined, "it appears that housing of hens in cages constitute[s] a decreased risk for outbreaks," note Eriksson and co-workers.
They add that the bacterium is thought to spread mainly through the fecal-oral route and that the differences in their findings according to housing type "may be attributed to the fact that laying hens housed in litter-based systems are continuously exposed to faecally contaminated litter and equipment in contrast with hens in cages."
They conclude: "In the future, a general vaccination of free-range flocks may be considered, but further documentation of the risk for outbreaks in free-range flocks are desirable," including investigations on the presence of E. rhusiopathiae in wild fauna.
By Sarah Guy, medwireNews Reporter