The particularity of the animal feed industry is that we are serving a herd of animals and the performance of the feed needs to be guaranteed for all animals. Homogeneity is an important criterion for the farmers. It is actually the growth of the weakest animals that will determine the farmer satisfaction. To ensure this homogeneity, feedmillers need to ensure that all the animals fed receive the proper amount of each nutrient. We saw in last month article that this exercise is difficult given that raw materials batches are themselves very variable. But mixing is another important milestone to ensure sufficient homogenization of ingredients... ...and it is much more critical that we think!!!
To monitor mixing efficiency, we are measuring coefficient of variation by comparing the composition of several samples taken from a same mix. We normally find higher variation for micro ingredients. The standard method is to use salt as tracer and to aim at reaching a coefficient of variation of 5% versus the targeted average. Practically, it means that we will have 68.2% of chances that the sample we collect will be within the targeted average plus or minus 5%. Or that 95.6% of the samples will be within the average +/- 10%.
This information means that if you want that 95.6% of the animals fed with your feed get sufficient nutrient for sure, you need to exceed the nutritional recommendation by 10%. And we all know that is very expensive…more than a company profit. This is what is happening when we are mixing 2 ingredients together. But when we are mixing 3, 5 or 10 ingredients, the chance that a sample contains the right amount of each nutrient is getting lower. The table below illustrates the evolution of the distribution depending on the number of micro ingredients you are mixing. The macro ingredients normally have a better CV% and do not affect that much the feed homogeneity.
This table shows that when you are incorporating 4 micro ingredients with a mixing CV% at 5%, only 21.6% of animals will receive all required nutrients (+/- 5%). If you cumulate this bias with the variability of the raw materials, you will realize easily that the performance of our formulation is quickly limiting by our industrial abilities.
The trial on the left underlines the negative impact on feed performance resulting from higher CV%. There is no point discussing the level of incorporation of a micro ingredient if only a minority of animals benefit from it. It is more critical to work at improving the mixing properties of the ingredients and reduce the CV%. Here are some best practices:
1 – Select the right form of micro ingredients The choice of the particle size and flow ability properties of the micro ingredient is critical. Ideally, all particles should get similar size to mix well. The flow ability will depend as well on the relative moisture of ingredients 9minerals and vegetal meals) and electrostatic phenomenon between particles (vitamins and argiles). There are some simple tests to implement to measure the flow ability of ingredient (click here to see the video angle of repose test) . This video is illustrating the differences of flow ability, particle size distribution and dust content between different sources of zinc oxide. The pictures are self-explanatory. 2 – Invest in an effective mixer Mixer is not the machine where we pay the most attention. But a mixer with a CV% just 1 point better will enable you to narrow your security margin closer to your targeted average and will make you save a lot with a very quick return on investment. 3 – Respect filling ratio and mixing time of your mixer Most mixer manufacturers suggest an optimal filling ratio of 70-85% for their mixers. However, a field study carried out by Evonick in ten countries, testing 30 mixing lines in the years 2006 and 2007, found that only 40% of mixers were operating within this range. The others had either a lower or a higher filling ratio. The wrong filling ratio of the mixer can have a negative influence on the feed homogeneity and increase the mixing CV%. This effect is more pronounced when liquid ingredients are used. In case you want to increase your mixer productivity, you will have the choice to increase either the filling of each mix or reduce the mixing time. Both will negatively impact but I recommend you to reduce For example, when considering an increase of mixing line output, the two basic options are to increase the bppatch size (keeping cycle times constant) or to reduce the cycle times at constant batch size (ie. Produce more batches per hour). Taking into consideration the effects on homogeneity, a reduced cycle time would have a less negative impact than overfilling the mixer. 4 - Optimize the order incorporation of your ingredients The order you will use to incorporate your ingredient will impact the homogeneity of your final mix. You may need to define the optimal order related to your specific formula 5 – Act promptly Even after mixing, the situation is getting worse as ingredients tend to separate when feed is stored, especially if particle size and atomic weight is different between ingredients. Therefore, it is critical to act quickly between mixing and pelleting. Premix should not be stored more than 3-4 hours and mix must be pelleted as soon as it is finished. Otherwise, ingredients will spontaneously separate and the pellet variability will even increase further. When working on this article, I realized that during my years at the head of Proconco, I did not pay enough attention on the statistical distribution of ingredients. Improving the CV% of the mixing operations by 1 point enable us to save up to 2% of feed cost equivalent to nearly 30-50% of our profit. I encourage you to develop a specific project aiming at assessing the mix ability of each of your ingredient. Your customer will thank you for that.