Silage analysis this year has shown that in many cases the pH of the silage is higher than we would like it to be. Higher pH levels indicate the silage has fermented poorly. This can be as a result of the grass being wetter at the time of cutting. Silages with higher pH levels are less stable on storage and more prone to spoilage and bacterial growth. It should be remembered that drier silages/haylages will be more stable on storage so are less risky even if the pH levels are high.
As well as the pH levels in the silage it is important to look at the ash content of the silage. This gives you an indication of the level of soil contamination in the silage. The normal ash content of silage is around 40 to 70g/kgDM. High levels of above 100g/kgDM suggest soil contamination and provide an early warning that the risk of listeriosis is increased.
The storage conditions of silage should not be ignored. Even well fermented silage without soil contamination becomes a listeriosis risk if there is damage to the plastic sheeting in pits or wrapping in bales. Bird proof netting is essential on many farms to reduce the risk of damage to the plastic. Any bales or areas of the silage pit where there is evidence of spoilage should be discarded.
When silage making and storing goes wrong it can lead to major health problems in the animals receiving the feed.
Sheep are more susceptible to becoming affected by listeriosis than cattle so good quality, well fermented silage is essential. The clinical signs likely to be seen when sheep are affected are drooping of one side of the face and turning in circles, followed by being unable to stand, and ultimately death. Abortions also occur as a result of Listeria infection and tend to cause an infection of the womb which can result in ewe sickness and death as well as the loss of lambs. Listeriosis is almost always due to feeding of soil contaminated or spoiled silage.
When feeding silage to sheep ensure pregnant ewes are fed the best possible silage. Do not feed visibly spoiled silage. Remove any uneaten silage from feeders within 24 hours to prevent continuing spoilage. Although cattle are less susceptible to listeriosis than sheep it does still happen. Pregnant cattle should not be fed silage with any visible signs of spoilage due to the risk of causing abortion.
Marion McMillan, Veterinary Investigation Officer, SAC Consulting
Sign up to the FAS newsletter
Receive updates on news, events and publications from Scotland’s Farm Advisory Service