An outbreak of iritis and uveitis in dairy cattle at pasture associated with the supplementary feeding of baleage

Authors: Laven RA, Lawrence KR
Publication: New Zealand Veterinary Journal, Volume 54, Issue 3, pp 151-152, Jun 2006
Publisher: Taylor and Francis

Animal type: Cattle, Livestock, Production animal, Ruminant
Subject Terms: Bacterial, Diet/rations/food, Eye/opthalmology, Nutrition/metabolism, Hay/silage/balage, Inflammation, Disease/defect, Infectious disease, Clinical examination, Pasture/crop
Article class: Correspondence

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Abstract: Ocular disease associated with infection by Listeria monocytogenes has been reported in the veterinary literature for over 30 years (Kummeneje and Mikkelsen 1975), however it remains a poorly defined condition (Morin 2004). Ocular listeriosis has generally been reported as having a similar disease pattern to that associated with listerial abortion or meningoencephalitis, i.e. the disease is primarily sporadic in occurrence although outbreaks can occur (Morgan 1977; Bocklisch et al 1991; Khodakaram-Tafti and Ikede 2005). However, Watson (1989) reported an outbreak of iritis and anterior uveitis in housed cattle linked to ocular infection with L. monocytogenes and associated with the feeding of silage. Since then, bovine iritis, commonly referred to as ‘silage eye’, has been increasingly recognised as a syndrome in dairy cattle in the United Kingdom (UK). Indeed, outbreaks of iritis are now more commonly reported by veterinarians in the UK than infectious bovine keratoconjunctivitis (Watson 2004), and a recent postal survey of dairy farmers in the UK found that bovine iritis accounted for over 80% of cases associated with L. monocytogenes infection, while nervous signs accounted for <5% and abortion for <3% (Erdogan et al 2001). Outbreaks of L. monocytogenes-associated bovine iritis have almost exclusively been associated with the feeding of silage. In such cases, the source of the bacterium is primarily soil contamination of the grass during cutting and/or wilting. In addition, bovine iritis is more commonly associated with the feeding of silage preserved in bales (baleage) rather than in stacks or pits. This is because in order to produce clinical disease the bacterium needs to survive the fermentation process, and one of the main factors determining its survival is the pH of the silage (Pauly and Tham 2003). The fermentation of baleage is less extensive and slower than that of pit silage (Ohlsson 1998). This means that its pH is generally higher than that of pit silage, often remaining >5. Consequently, Listeria spp are more likely to survive in baleage than in pit silage. Despite the widespread use of baleage in other countries, ocular infections due to L. monocytogenes have been primarily reported in the UK. However, it is likely that such infections are present worldwide and that the lack of reports indicates a lack of investigation rather than absence of disease (Evans et al 2004). We describe here an outbreak of bovine iritis in a herd of dairy cattle in New Zealand fed baleage while at pasture…

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