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Increasing need for microbial control in liquid feeding

Liquid feeding systems can be very interesting for the pig industry as they reduce feed costs. Financial benefits, however, are only achieved if feed hygiene and microbial control are adequately taken into account. In recent years there has been a trend in decreasing microbial quality of relevant raw materials. This stresses the need for appropriate preservation of these materials.

Liquid feeding systems can be commonly found in the pig industries of Northern Europe. Over 60% of slaughter pigs in Denmark and Sweden are fed liquid feed, and so are the majority of Danish and Swedish sows. Liquid feeding levels in slaughter pigs in both the Netherlands and France are said to be at around 33%, but it is estimated rates are 50-60% in their main pig regions.

A key reason for using liquid feeding systems is the possibility of using liquid raw materials (co-products from the food industry) and dry raw materials, thus reducing total feed costs. This reduction, however, can only be achieved if feed hygiene and microbial control of the raw materials are taken into account.
Examples of liquid feeding products with good microbial control (left) and with undesired microbial activity leading to gas formation (right).
Yeasts, moulds, Enterobacteria and Lactobacillusbacteria are common micro-organisms present in liquid feeds and their liquid and dry raw materials. Lactobacilli have a positive reputation for fermentation processes; the others, however, have negative effects in more than one way.
Degraded lysine levels
Firstly, moulds, yeasts and Enterobacteria all consume main ingredients of feed materials, deteriorating the nutritional quality. Moreover, their presence may lead to a reduced palatability and related lower feed intake of animals. Yeast and moulds are known as important spoilage bacteria, converting proteins, fast sugars and/or starch into carbon dioxide and water, reducing the feed’s dry matter content.
Yeasts and in particular Enterobacteria in liquid feed may cause degradation of protein and especially lysine levels. Research conducted in Denmark showed that about 17% of added synthetic lysine was lost after 24 hours of storage of fermented liquid feed. This loss is likely due to preferential utilisation of free amino acids by microbes found in fermented feeds.
Secondly, moulds, yeasts and Enterobacteria may negatively affect intestinal health of animals. The effect may be directly (Enterobacteria are pathogens themselves, like E.coli and Salmonella), or indirectly via production of high levels of gas in the intestines and toxins. Consequences of deteriorating nutritional quality of raw materials and negatively affecting intestinal health of animals are reflected in a reduced technical performance and health status of animals. Therefore, an appropriate control of yeasts, moulds and Enterobacteria is needed to achieve the financial benefits of liquid feeding systems.
Decreasing trend
In recent years, several market developments have negatively been affecting the microbial quality of liquid feeding products. Nutrient levels in co-products have decreased as extraction procedures in the food processing industry are constantly improving. The result is a reduced availability of nutrients for Lactobacilli leading to less pH reduction in the liquid raw material. Next, the co-product inclusion level in liquid feed diets has lowered due to limited market availability.
This resulted in higher inclusion levels of raw materials like barley, wheat and soybean meal to complete these diets as alternative energy and protein sources.
Analysis showed that the microbial contamination by especially Enterobacteria increased in co-products and liquid feed diets in recent years (Figure 1). In 2008 and 2009 up to 55% of the liquid feed samples showed a pH above 4.5 whereas in 2007 it was 42%. Enterobacteria can survive in an environment at a pH larger than 4.5 and may grow out in the liquid feed. In line, Enterobacteria become more and more a trouble causing micro-organism at commercial farms with a liquid feeding system.
The increased use of cereals in liquid feeding most likely also contributed to higher contamination levels of Enterobacteria. Especially barley used at commercial problem farms showed high levels. Enterobacteria in contaminated ground cereals can develop easily at a high pH in liquid diets.
This is the result of the lack of a heating step in the process. During processing in a liquid feeding system, cereals are ground with a hammer mill in a non-conditioned environment. This way the natural protection is broken down with the effect that the present Enterobacteria easily can develop (Figure 2). In contrast, feed mills can more easily deal with contaminated cereals. In feed mills these cereals are ground, subsequently mixed with other nutrients and finally pelletised. Due to the temperature during pressing, Enterobacteria get killed.
The use of organic acids
Organic acids form a product group that can successfully be used for microbial control in liquid feeding applications. Each organic acid has its own physical and chemical characteristics, leading to specific anti-microbial activities. By combining acids in blends, the product gets a broad spectrum antimicrobial functioning, leading to a more effective control at low dosage. This makes it a good match for co-products and liquid feed diets because of the need for controlling Enterobacteria, yeasts as well as moulds.
The concept of blending of organic acids (Selko BE+) was e.g. tested during an experiment at a problem farm with 3,000 fattening pigs. An analysis of all raw materials used revealed that the co-products whey and especially brewers’ yeast were the main cause of the problems (both yeasts and Enterobacteria). Treating the brewers’ yeast with this organic acid blend reduced and prevented nutritional losses reflected by a positive effect on dry matter (+3.6%) and lysine content (+0.3%). It is known that particularly Enterobacteria are responsible for the degradation of lysine. The adequate microbial control of risky raw materials resulted in an improved technical performance indicated by a higher daily gain and a lower feed conversion ratio and mortality (Table 1).
Blends of organic acids are effective in controlling Enterobacteria, yeasts as well as moulds at farms with a liquid feeding system. Monitoring the microbial status of raw materials and liquid diets is the first step. Next step is focusing on relevant co-products or bottlenecks in the feeding system, and selecting the best combination of organic acids. This way application of organic acids may be optimised improving the preservation and leading to a better animal and financial performance.
References available on request.
Source: Pig Progress Volume 25 nr 8


Maarten van der Heijden and Jaco Eissen, Trouw Nutrition International – Feed Additives

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