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Evenly mixed feed essential for consistent livestock performance
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by Christian Rabe, Applied Feed Technology, Evonik
nsuring animal feed is uniformly mixed is important as it means that all added nutrients are available evenly within every feed ration. It is vital that the essential and low-dosed ingredients, including vitamins, trace elements, minerals, amino acids are available in the right volume within each final feed pellet. A study conducted with 240 Ross broilers in a 42-day grow-out period by Ciftci and Ercan (2003) shows the impact of mixing homogeneity, expressed as coefficient of variation (CV) on important livestock performance factors. Feed intake and feed conversion rate (FCR) show a moderate improvement with better feed homogeneity (10% CV vs 30% CV). At the same time, flock homogeneity improved significantly which is an important economic factor. The efficiency and the profitability of the production of live animals will be directly impacted by the homogeneity of mixed feed. As a rule, homogenous feed mixes with a CV of five percent or below can be technically achieved under commercial conditions and are considered as optimal for livestock performance, particularly poultry. In this context, it is important that the analyte and assay which are being used for assessing homogeneity are suitable, sensitive and accurate to pick up the variation. The following ranking for the CV of feed additives in finalised feed is commonly used: Cv < 5% Cv 5 â&#x20AC;&#x201C; 10% Cv > 10% Optimum Homogeneity Acceptable Trouble-Shooting Advisable
In regular feed production, mixing homogeneity is sometimes not managed well. Of nearly 100 commercial feed mixers tested, approximately 51 percent had mixing CVs less than 10 percent, and 19 percent of the mixers had CVs greater than 20 percent (Vogel and Laudert, 2015). There are numerous factors influencing the mixing homogeneity of final feed. One important factor is the incorporation of liquids. Even below an addition rate of three percent, special 56 | November 2020 - Milling and Grain
care has to be taken to achieve results comparable to the dosing of dry ingredients. The added liquids should be mixed longer than the dry ingredients to ensure homogeneity and to break up agglomerates that will have formed. There is the risk that, if the dosing technique for liquid addition is suboptimal, small lumps might form which are not dissolved during the mixing process, eventually leading to larger agglomerations (Behnke, 1996; Froetscher, 2005). To break up the lumps and increase mixing homogeneity, high-speed paddle mixers with spraying systems suitable for the dosed product are required. The positioning of liquid additions into the mixer and the additional wet mixing time are important to achieve homogeneity of the final feed. Also, liquid dosing systems require additional cleaning and maintenance of nozzles to prevent poor mixing results (Clark, 2009). With the time required for spraying liquids, optimal mixing time is often compromised in order to not extend batch time and reduce mill throughput. That typically leads to poorer mixing quality. It is critically important that the liquid spraying system is being operated and maintained with care to avoid fouling, which will reduce mixing homogeneity and result in under-dosing of the
Figure 1: Overall results for mixing homogeneity (CV) for amino acids added as dry bulk (n=612) in comparison to their liquid analogues (n=211). ( CV of 0 â&#x20AC;&#x201C; 10% considered acceptable by most feed industry standards)