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Homogeneity of additives in the feed

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Ricardo Hume Ricardo Hume
Agricultural Engineer
May 17, 2020

Marc,
In my opinion a CV = 10% is no good enough. It means that the additive is present in the feed at plus or minus 20% of the average intended dose. I don't think this is acceptable, at least for poultry.
A CV = 5% means that the distribution of the product is between plus or minus 10% of the average; this is what I consider a satisfactory distribution for an additive.

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Marc Perel Marc Perel
Solution Application Manager,
Adisseo Adisseo
Oost-Vlaanderen, Belgium
May 17, 2020

Dear Ricardo Hume
Thank you for your comment and your interest in this video.
In order to avoid any misunderstanding regarding the interpretation of the CV, let me clarify that, considering a normal distribution of the additive in a batch of feed (Gauss curve), a coefficient of variation (standard deviation/mean value) of 10% means that 68% of the mass of the batch contains between 90 and 110% of the mean value, 95% between 80 and 120% and 99% of the mass of the batch contains between 70 and 130%.
A value of 10% is commonly accepted in animal nutrition. For example, the European Feed Manufacturers Guide established by the FEFAC mentions that “a target maximum percent coefficient of variation (CV) and mean percent recovery must be established taking into account the analyte, the target levels and background values. In most cases, a target CV of less than 10% should be achieved.”
I am not a zootechnician, but I would say that the criticality of the heterogeneity of an additive depends on several factors: notably the nature of the additive and its rate of incorporation in relation to the needs of the concerned animal (and the daily feed intake). An elephant may be more tolerant than a shrimp...
In any case, and I agree with you on this point, it is up to each manufacturer to determine its own quality standards, which may go beyond the good practices codes and regulatory requirements.
Kind regards, MP

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Ricardo Hume Ricardo Hume
Agricultural Engineer
May 18, 2020
Marc, see what other experts think about a CV = 10%.

All About Feed Magazine
Wayne Cooper
Feed mill and machinery expert
Expert opinion
18 May 2020

The CV of

Ok, so this is a pet peeve of mine. This standard has been in place since 1985….forever! Is it not time to step up our game? I had actually thought our major challenge would always be medications. However, as medications are cut back, we are now getting multiple products to replace them. Enzymes, probiotics, herbs, you name it. Whatever it is, it is concentrated to small addition rates. We need to evenly spread it throughout the batch. At one of the mills I supervised, we were operating a “5 ton mixer” at 110 tph and CV’s under 4. If you are looking
at a new mixer for any reason, do you want to go with “OK” CV’s of <10 for the next 30 years? you can do better if you check around.
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Marc Perel Marc Perel
Solution Application Manager,
Adisseo Adisseo
Oost-Vlaanderen, Belgium
May 19, 2020
Dear Ricardo Hume

I do not want to give the impression that there is any disagreement between us or even that I am downplaying the importance of the homogeneous distribution of additives in food, quite the contrary! My speech is as follows: monitor the performance of the mixers regularly (every year), set limits for the recovery rate and CV, implement corrective actions if the results are outside these limits. A simple quality approach in short.
My job is precisely to bring nutrition and technology closer together and your interest in what happens in the plant is very important in this respect.
Concerning this CV limit, by default I say 10% (common reference in regulations and quality standards), you say 5%, it's fine. And obviously, more demands will be placed on a new installation than on an installation that has been in operation for several years.
In any case, my colleagues and I are always available to help our customers achieve their quality objectives, in any context.
Yours sincerely,
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May 19, 2020
Interesting comment about the CV's of mixer tests and the 1985 date for the 10 % CV acceptability. While employed at Degussa, now Evonik in the 1980's mixer profliles were offered as a customer service. At that time a standard was needed to compare for % CV's for mixer profiles. The standard at that time, around 1985, was the Kansas State research on mixer profiles using the QuanTab salt assay. This data indicated that a good feed mixer in the 1980's could achieve a CV of 10% using this somewhat variable assay. Mr. Perel's comments are very well stated and very good for statistics and establishing goals for probably of having a certain nutrient level..
However, as Mr. Hume points out we can and should do better than the old standard of 10%. A new standard from my experience with assaying for added methionine in a good laboratory for assays is a CV of 2-3 % above the variation of the assay being conducted.
In my experience the added methionine assay has an assay variation of 2-3 % for the assay itself ,assaying 20-30 samples over a period of several days. Thus, a very good feed mixer with an addition rate of 4-6 pounds of methionine per ton should have a CV of 5-6%. Not the old 10 % CV that was established with the variable assay in the late 1970's- 1980's.
The feed mixers that I used achieve this performance level for methionine additions. The methionine assay is a good assay for the general condition of the mixer because the added test substance is added in the range of most micro feed additives 1-8 pounds per ton and thus test the mixing of ingredients added a lower addition rates and the bulk density of methionine is at a mid point of most feed ingredients other than minerals.
Minerals with their higher density should be tested with a different assays . Calcium is a difficult nutrient to achieve good CV's for in diets. Part of the problem is that we tend to use the same laboratory tests to assay for calcium in ingredients that have levels of 0.1% calcium or less to finished feeds that have levels of 0.8 to 3.5 % calcium and compound the assay problem by using either finely ground limestone or coarse limestone particles as the limestone source in these feeds. The solution is the same as above, optimize the assay for the amount and form of nutrient source (calcium) being added and the addition level added and then conduct the mixer profiles.
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May 27, 2020
Dear Sirs, thanks for info. In case of liquid products spray methods, CV=10% is ok. But when we mix powder to powder, we have much more problems. At first, this is ditterent density weight of additives. At second, this is transportation. Vibration of cargo often caused mix stratification. Often is necessary to make re-mixing after transportation, before to feed animals.
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Ricardo Hume Ricardo Hume
Agricultural Engineer
May 27, 2020
Dear Fiodor.
If I want to add 4kg of liquid methionine / ton of feed with a CV=10%, that means I am willing to accept a dosage range of 3.200 - 4.800 kg (considering plus or minus 2 standard deviations). This is a very broad range in my opinion. I still think that the CV must be 5% for liquid products as well.
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Marc Perel Marc Perel
Solution Application Manager,
Adisseo Adisseo
Oost-Vlaanderen, Belgium
May 27, 2020
Dear Ricardo Hume ,


Please let me comment your last message to avoid any confusion:

On one hand, we speak about homogeneity of repartition of an additive in a batch of feed, where the CV translates the variability between N samples taken from a same batch. I mentioned that a CV of 10% is acceptable, you prefer to say 5%, it is OK, I will not comment further.
On the other hand, you mention "...a dosage range of 3.200 - 4.800 kg", addressing the dosage accuracy, which is another topic. Usual technical means (by scaling or flowmetering) generally allow accuracies of 1% or less to be achieved.
Both notions (homogeneity & dosage accuracy) are complementary to reach the conformity of the finished feed.
Best regards, Marc
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Ricardo Hume Ricardo Hume
Agricultural Engineer
May 27, 2020
Marc Perel
Thank you Marc for your comments.
I totally agree with you that a dosing accuracy of 1% is excellent. This means that when you add 4kg of a product / ton you will find samples between 3.960 kg and 4.040 kg/ton.
That range represents a CV = 0.5%.
Best regards, Ricardo
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May 28, 2020
Ricardo Hume Dear Ricardo, 100% agree with your opinion. CV 5% is easy to reach, because if we will spray methionine into the mixer, during the mixing process, feed mix becomes to be (theoretically, if mixer is well adjusted) 100% homogenic, in splite of different size and specific density of ingredients. After the end of mixing process, during feed transportation, stratification is possible, but it is any case not stratification of methionine, because different feed ingredients, after spraying, already have the same methionine content! In case of pelleted feed, stratification is no problem at all.
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