Silage Insights - Bale Silage Production
Focus on bacteria: Listeria and Clostridium

Relationship between the contamination in LM and pH

Source: PEP Bovin Lait Rhône Alpes, Institut de l’Elevage

Listeria monocytogenes in high numbers can be pathogenic to ruminants, causing meningitis, septicaemia and spontaneous abortion. It also can be dangerous for people that are frail, such as the elderly, and for women that are pregnant. Clostridium tyrobutyricum is not pathogenic but causes off flavours in milk and cheese. Both can be found in the soil and water.

A study conducted on 55 sites in the Rhône Alps, in 1995–6, showed optimum conditions for these bacteria to flourish are presence of moisture, absence of oxygen, suitable temperature and available nutrition. They also need a pH value that is not too low. Proliferation of the bacteria can be inhibited by ensuring the pH is reduced promptly by the action of lactic acid bacteria immediately after the silage is made. A pH below 5.2 will inhibit Listeria and lower than this can destroy it. If it is not low enough, falls too slowly or is allowed to increase again, there is a risk from these bacteria.

Recommendations

Recommendations coming from the study include removal of mole hills in the spring, before cutting for silage, harvesting the forage while it is young, cutting at 6 – 7 cm and turning the forage at least once while it is drying. Bales should be well compressed and tightly wrapped with four or six layers of good quality wrap 750-mm wide. They should be stored carefully on a clean, sound surface and protected with nets, bird scarers and rodenticides.

The bales should be inspected frequently for damage and any holes should be repaired promptly with special adhesive tape. When the bales are used, silage near any damaged areas should be removed and destroyed. If milk is being used raw for cheese production, only undamaged bales should be fed to the dairy herd.

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