Background last update:6 Aug 2012

Controlling hygiene in liquid feeding systems

Liquid feeding systems are widely used in Europe and in recent years became very popular in North America and other regions of the world. This trend is most probably not only driven by the positive effect of liquid feeding on performance, but also by extremely high feed prices and the increase in biofuel production, which makes cheap mainly moist by-products available in high amounts. However, in order to achieve the benefits in performance high hygiene standards have to be maintained.

The beneficial effects of liquid feeding sows, weaner, grower or fattener pigs are well known. The usage of liquid feed in weaning pigs is obvious. The newly weaned pig is withdrawn from the sow’s milk after weaning. Continuing with a liquid diet seems to be more suitable for the piglet at least for a certain period of time. Positive effects are seen in terms of feed intake after weaning resulting in an improved performance.

The increase in feed intake post-weaning by supplying liquid feed was shown to help maintain gut integrity and in particular villous height. Villi regression can often be seen in pigs immediately post-weaning. Avoiding this phenomenon can help to maintain the digestive capacity of the pig and can help the newly weaned to overcome the post-weaning growth-check more easily. Also for pigs in other production stages and for sows liquid feeding has advantages. Gut health can be improved, which leads to a reduction in medication and an improved animal well-being. Furthermore, an improved nutrient utilisation is a distinct advantage for animals in all production stages.

The usage of by-products
Considering the current pressure on pricing that producers experience at the market, a real advantage of liquid feeding is that by- or co-products from the human food industry or biofuel production can be used. Those products are available at cheap prices so that the producer can keep production costs low. Especially the increase in biofuel production is leading to a kind of awkward market situation. On the one hand the increased demand for conventional feed stuff due to the increase in biofuel production is leading to an increase in prices for conventional feed stuff, putting enormous pressure on livestock producers. On the other hand, the co-products from biofuel production are available in high amounts and at cheap prices. Market experts expect an almost seven-fold increase in biofuel production from 12 billion gallons in 2005 to around 83 billion gallons in 2030. This might lead to the conclusion that liquid feeding remains popular as in such systems by-and co-products can be used in high amounts.

Challenges feeding wet feeds
There are many challenges when using liquid feed. Those challenges arise mainly due to the usage of by-products. The consistency of the by-products is one major issue and livestock producers should make sure that the quantity and quality of by-products is guaranteed. Some by-products have a high water content, which makes it difficult to justify long transportation distances as the transportation costs per kg dry matter are high and the manure volume produced by pig units can increase which does not add to the sustainability of agricultural production. Also the variability in nutrient content of by-products can vary from batch to batch and frequent sampling of the products is required in order to avoid feeding insufficient or excessive amounts of nutrients to the animal.

However, the most pronounced problem when using liquid feed is the hygiene issues such systems carry. A high hygiene standard when using liquid feed is required in order to avoid detrimental effects on growth performance. So surfaces in feed storage and processing areas should be kept clean and food splashes should be removed on a regular basis in order to prevent the growth of moulds. But even if normal hygiene preventions are in place the risk of contamination of liquid feed with microorganisms is still present.

Microbes in liquid feed
Liquid feed provides an ideal medium for yeasts, moulds, lactic acid bacteria and Enterobacteria. These microbes might have adverse effects on growth performance as a certain amount of nutrients are lost to the microbes and not available for the host animal. Furthermore toxic metabolites might be formed by those microbes and possible inflammatory processes might be required to defend the host organism. Besides that, the presence of those microorganisms might have adverse effects on feed intake due to reduced feed palatability.Yeasts and moulds are spoilage bacteria which convert proteins, sugars and starch into carbon dioxide and water. This not only reduces the feed’s dry matter content, the development of carbon dioxide may result in increased aggressiveness and increased mortality due to intestinal distortion and inner bleeding when consumed. Yeasts and Enterobacteria in liquid feed may degrade protein and it was shown that especially lysine is mostly affected by degradation. However, it has to be mentioned that losses mainly occur in free amino acids. Therefore, microbes such as moulds, yeasts and Enterobacteria need to be controlled in liquid feed in order to maintain hygiene standards of liquid feed and achieve economic benefit. How the microbial load in feed can be controlled and feed hygiene be maintained was shown at a commercial farm in Austria.

The first step in maintaining a good hygiene in liquid feed is the continuous analysis of the raw material. Analysis of the raw material used at an Austrian farm is shown in Table 1. As it can be seen from the guideline values shown in Table 2 the mould count in rye and wheat and yeast counts in corn as well as whey were above tolerance levels. Acceptable and limiting values for bacteria, moulds and yeasts for finished liquid feed are shown in Table 3. In general yeasts and bacteria should not exceed 5×106 cfu/g liquid feed and moulds should not exceed a level of more than 10×103 cfu/g liquid feed. However, tolerance levels may vary between stages of growth.

Organic acids to maintain feed hygiene
Organic acids are a product group most suitable for the control of yeasts, moulds and bacteria. Using a blend of organic acids furthermore broadens their spectrum of activity as each organic acid has its own characteristics. In a trial at an Austrian farm a mixture of formic, propionic and lactic acid (Biotronic SE forte liquid, Biomin Holding GmbH) was used in liquid feed and feed hygiene was examined.

The feed was treated with 0.3% (3 ltr/1000 ltr) liquid feed of the organic acid mixture and the water pipes were filled with a solution of 3% of the acid mixture dissolved in water which remained in the pipes over night. Afterwards, the feed was analysed for its yeast content at different stages of feed preparation and distribution. Results of the feed analysis for yeasts are shown in Figure 1.

Samples were taken in two different barns and repeat determination was carried out to reduce analytical mistakes in the trial. The amount of bacteria and moulds found was within the tolerance levels. The amount of yeasts was tolerable within the tank, but above tolerance levels in the down pipe and trough. The samples from the tanks basically serve as the control samples in between the groups. In the control feed yeast counts were 1.5 fold increased in the down pipes, twice as high in the trough with fresh feed and 3.6 fold higher when feed residues were taken from the trough.The addition of the acid mixture lowered the pH of the feed from 5.57 to 4.89. This resulted in a reduction of the yeast contamination of the feed in the trough with fresh feed and an almost elimination of yeast counts when residues were taken from the trough. Especially when it comes to the residues in the trough the reduction in yeast counts is very beneficial, as residues in the trough might contaminate the freshly prepared feed.

In conclusion
Adding a mixture of propionic, formic and lactic acid to liquid feed gives the possibility to effectively control bacteria throughout the distribution channel of the feed, which leads to improvements in growth performance. Furthermore, there are not only the beneficial effects of acidifiers on feed hygiene but also on animal growth performance directly, providing further beneficial effects for the livestock producer.


Angela Riemensperger, Biomin, Herzogenburg, Austria

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