Fundamentals of proper feed preservation
Processing treatments and storage conditions influence the population levels and the types of microorganisms present in the feed. Many moulds are toxigenic and produce mycotoxins. Conditions favouring mould growth include moisture levels, warm temperature, oxygen presence and prolonged storage time. A multitude of steps must be taken to secure the hygienic status, e.g. thermal treatment and addition of chemical compounds to control microorganisms in feed. The addition of organic acids has been shown to contribute to environmental hygiene, preventing feed raw materials and compound feed from microbial and fungal deterioration. Supplementation of organic acids in compound feed tends to decrease the feed pH, buffer capacity and to prevent undesirable microbes' growth. The bacteriostatic activity is thought to derive from the penetration into bacterial cell and their dissociation there. After penetrating the bacteria cell wall, the non-dissociated form will be exposed to the internal pH of bacteria and dissociate, releasing protons (H+) and anions (A-). The internal pH of bacteria will decrease and because the bacteria cannot tolerate the a large spread between internal and external pH, as specific mechanism (H+ -ATPase pump) will act to bring the pH inside of the bacteria to a normal level. This phenomenon consumes energy and eventually can stop the bacteria growth or even kill it (Lambert and Stratford, 1999). The anion part of the acid is trapped inside of bacteria because it will diffuse freely through the cell wall only in its non-dissociated form. The accumulation of A- becomes toxic for the bacteria.
The constant treatment with organic acids has a residual protective effect in feed. It helps to reduce recontamination of the feed risk and to minimize the contamination of milling and feeding equipment. For each organic acid, its specific inhibiting effect on bacteria, yeast and mould has to be considered. For example, formic and propionic acids have broader antimicrobial activities and can be effective against bacteria, fungi and yeast, whereas lactic acid is more inhibiting on pathogenic bacteria. According to various literature sources, the efficacy of the products depends on 1) type and dose of supplemented acid, 2) type of the feed and its buffer capacity, 3) hygiene standards in the feed mills, 3) processing method of feed.
In the present trial, the efficacy of a product based on formic and propionic acids (Biomin® product) against moulds has been tested in vitro by adding different amounts of the product and water.
The feed samples, with dry matter (DM) content 89.19 were divided into 6 groups:
1. Group 1: 2 ml Biomin® product/kg feed
2. Group 2: 1 ml Biomin® product/kg feed + 10 ml H2O/ kg feed
3. Group 3: 2 ml Biomin® product/kg feed + 10 ml H2O / kg feed
4. Group 4: 2 ml Biomin® product/kg feed + 15 ml H2O / kg feed
5. Group 5: 3 ml Biomin®product/kg feed + 15 ml H2O / kg feed
6. Group 6: no feed additive, no water
The feed samples were stored at different temperatures and different relative humidity (HR): I) 20°C 85% HR; II) 35°C 85% HR. The results of the present study showed that the feed stability is directly related with the added amount of the Biomin® product, temperature and moisture content (Figure 1). Overall in the temperature 35°C, the feed was stable for a shorter period, compared to that stored in temperature 20°C with 85% HR.
At the temperature 35°C with 85% HR, the longest storage time was determined in Group 1 where only the Biomin® product was added at 2 ml/kg feed, followed by the Group 5 where the Biomin® product and water were added at 3 ml and 15 ml per kg of feed respectively (Figure 1). At the temperature 35°C with 85% HR, the shortest storage time was determined in the Group 6, followed by Groups 2, 4 and 3. At the temperature 20°C with 85% HR, the storage time was equal in Groups 6, 4 and 2, followed by Groups 1 and 3, and Group 5.
The feed storage duration in relationship with the results of the present trial should be interpreted with awareness. The present trial was carried out under laboratory conditions. However, under practical conditions, feed storage time might be shorter due to various factors, such as temperature and humidity fluctuation, bacterial burden, and difference in feed matrix.
A decrease in mould counts were determined in some raw feedstuffs added with the Biomin® product at 3 kg per tonne of feed. The storage time was 30 days at 22°C temperature with 57% HR (Table 1).
10 g of each sample were added to 90 ml of peptone water 0.1 % and kept at room temperature for 30 minutes. Mould counts were determined on malt extract agar (1.05398 MERCK, Germany), after incubation at 30°C for 5 days.
Table 1. Effects of the Biomin® product on the counts of moulds in some feed raw materials (logarithm of colony forming units per gram)
Conclusion: The Biomin® acid-based products could be used to decrease mould counts in feed raw materials and compound feed. The storage time depends on the temperature, relative humidity and microbial challenge.
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Article made possible through the contribution of Dr. Attila Kovács and BIOMIN Holding GmbH