Silage and livestock health

Silage making involves preserving forage crops by fermentation of water-soluble carbohydrates (sugars) to organic acids. The fermentation is relatively uncontrolled and inadequate acidification can allow the growth of undesirable microorganisms such as enterobacteria and clostridia. Ingress of oxygen to the outer layer of the silo or bale during the storage period encourages growth of yeasts and moulds. Mycobacterium bovis may survive in silages with pH above 5.0. Outgrowth of clostridia in aerobically deteriorating silage can lead to high counts of butyric acid spores in silage that can contaminate milk and cheese. Milk may be contaminated with Penicillium toxins and be rejected for containing antibiotics. Specific disease risks to livestock from poorly preserved silage include bacterial endotoxicosis, listeriosis, botulism, mycotoxicosis and nitric acid poisoning in addition to reduced feed value. Rapid acidification is essential once the crop is ensiled to restrict the growth of enterobacteria, listeria and clostridia. Oxygen barrier film, in addition to reducing loss of dry matter during the storage period, prevents clostridial outgrowth in the outer layer of the silo and is also likely to reduce the risk of listeriosis.