If silage is being cut after only 3-6 weeks of a field last being grazed there is a possibility that there could still be faecal contamination of the cut grass. The risks from this to the stock being fed it are likely to be relatively low, however it is likely to affect the feed quality of the silage.
Although Listeria can be passed in animal faeces it is probably present in higher numbers in soil so if silage is contaminated with soil, or if is there is spoilage in the pit or bale, then that is more likely to be a higher risk for infection of cattle and sheep. Listeria can cause abortions, infection of the brain and eye and also blood poisoning and deaths.
If cattle are shedding the Johne’s organism in their faeces and it is still on the grass when it is cut a few weeks later, there is evidence that it can still be found after ensiling. In one study there was no reduction in the numbers detectable after ensiling when tested with a quantitative PCR. However another study found that it could not be grown in culture after ensiling but it was still detectable in PCR testing. PCR tests will detect non-viable as well as live organisms but it has been suggested that it might be present after ensiling in an inactive or dormant state. Further work is therefore necessary to determine if this state could be a risk for causing Johne’s infection. However the risk is likely to be relatively low compared to other routes of infection, especially as calves in their first few months of life are most susceptible to the infection and they are unlikely to be consuming much, if any, silage at that stage.
If a herd is infected with Salmonella then cutting grass for silage soon after it has been grazed could be a potential risk for infection through the silage. There are reports of an outbreak of Salmonellosis linked to feeding contaminated silage but in other studies Salmonella has not survived the ensiling process.
Clostridia bacteria in faeces can interfere with the silage fermentation process. Therefore if there is faecal contamination of the grass then the silage made from it could be poorly preserved as the clostridia cause the pH to be high and there is less lactic acid and more butyric acid, which adversely affects the quality of it.
Catriona Ritchie, email@example.com
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