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New information about liver fluke risk from silage

“Can cattle or sheep be infected with liver fluke from silage?” has been a frequently asked question at farmer meetings over the last few years.  The answer has always been that the risk is likely to be low based on the facts that:

  • Silage fields will usually have been lightly grazed earlier in the year
  • The grass is usually cut before metacercariae numbers peak in autumn
  • The wettest areas of the field (where metacercariae numbers are likely to be highest) are not suitable for cutting

Researchers at Liverpool University have carried out experiments to determine whether or not Fasciola hepatica metacercariae are capable of surviving in silage.

Metacercariae were ensiled with grass that had been wilted to create samples with 20%, 30% or 40% dry matter, and their viability was assessed 2, 6 and 10 weeks later.  Where anaerobic conditions had been maintained all metacercariae were non-viable by 2 weeks post ensiling.  The pH of the silage samples ranged from 5.08 to 6.14 indicating some suboptimal fermentation.  No silage additives were used.

The same experiment was repeated under conditions representative of aerobic spoilage.  Viable metacercariae were detected at 2, 6 and 10 weeks in the 20% DM sample; 2 and 6 weeks in the 30% DM sample; and after 2 weeks in the 40% DM sample.  The pH range was 9.03 to 9.36.

The researchers concluded that:

  • There is no risk of F. hepatica transmission from anaerobically fermented silage fed from 2 weeks post sealing
  • Metacercariae can survive for a period of time under aerobic conditions and therefore spoiled forages may represent a risk particularly if the dry matter is low
  • Ensuring adequate wilting to increase dry matter and achieving a good seal to create anaerobic conditions remain key in the silage making process

The outcomes of this research are nice and clear and yet another reason not to feed any potentially spoiled silage. 

 

Reference: 

John et al. (2020) Anaerobic fermentation results in loss of viability of Fasciola hepatica metacercariae in grass silage.   


Posted by Veterinary services on 10/11/2020

Tags: Sheep, Veterinary services, liver, fluke
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