Holger Brecht
Sales Engineer | FRITSCH

Precise analyses are of central importance in the animal feed industry. They guarantee the quality of the products, compliance with legal requirements and ensure the health of humans and animals. Despite state-of-the-art analysers, however, inexplicable results occur time and again, raising doubts about the reliability of the measurements. The cause often lies in inadequate sample preparation. Therefore, adequate sample division and sample comminution are indispensable prerequisites for scientifically sound and reproducible analysis results.

An analyser - no matter how high-quality it is - can only deliver results as precise as the underlying sample allows. Sample preparation in terms of sample division and comminution is therefore a crucial step in the analysis, as it lays the foundation for reliable and accurate results. Precise results are particularly important when analysing feed for livestock farming. There are several reasons for this. Firstly, many countries have strict regulations and standards for analysing animal feed, especially for export products or in organic production. In addition, incorrect measurement of nutrients such as proteins, fats, carbohydrates, minerals and vitamins can affect the ration design and the nutrient supply of the animals. On the one hand, this has a detrimental effect on animal welfare and, on the other, favours delays and quality losses in breeding, which in turn can lead to additional costs. In addition, the analysis reveals any contamination of the feed with harmful substances such as mycotoxins, heavy metals or pesticides. Good sample preparation makes it possible to detect even the smallest amounts of these substances, which are dangerous for animals and humans.

WHAT MAKES A GOOD SAMPLE

The central task of sample preparation is to produce a sample that is as homogeneous and representative as possible in terms of form and composition. This is very challenging, as the basic population of a feedstuff, i.e. the entire batch, is usually much larger than the quantity that is actually analysed. In addition, feedstuffs are often heterogeneous mixtures of different components such as cereals, proteins, minerals and additives. For example, there is a wide variety of particle sizes due to different grain sizes of different components. In addition, individual components with different densities can segregate during sampling. The composition of a homogeneous sample is made even more difficult by the fact that modern analysers require ever smaller sample quantities, which requires a high degree of compactability. It is therefore particularly complicated to take a sample from the often-inhomogeneous mass that is as representative as possible for the analysis and that represents the entire batch and not just a part of it. The corresponding sample must reflect all relevant properties of the feed. Otherwise, inadequate sampling or sample preparation can lead to systematic and random errors that falsify the analysis results. What this means in detail can be illustrated with an example. If a feed manufacturer wants to determine the content of essential amino acids in a new feed batch, inadequate sample comminution can lead to larger particles being insufficiently extracted. This leads to an underestimation of the amino acid content. By using a suitable comminution process, however, the sample is homogenised, making extraction more efficient and the analysis results more accurate. A good sample, i.e. one that is representative and as homogeneous as possible with a high degree of standardisation, makes it possible to achieve consistent and reproducible results. Last but not least, these can also be used for medium and long-term quality assurance, as they establish the historical comparability of different batches.

Sample preparation plays a decisive role in analysing animal feed.

SAMPLING IS THE FIRST STEP

The first and most important step in sample preparation is to take a representative sample. This should contain all relevant components of the feed in the correct proportions in order to minimise incorrect analysis due to fluctuations within the batch. This first requires careful planning in terms of determining the sampling locations and times. A sufficient number of sub-samples should be taken from different areas of the batch and mixed later. The number and quantity of samples should be based on industry standards and the batch size. It is important to use suitable, sterile tools such as sampling probes and scoops to avoid cross-contamination. In addition, all relevant parameters for traceability should be recorded to ensure complete documentation. Overall, software-supported process recording and monitoring is recommended for sample preparation, as it helps to avoid errors and ensure traceability. The following example shows how adequate sampling can be organised in reality. A feed batch of ten tonnes needs to be analysed. To do this, the employees use a clean, sterile sampling device to take a 500 gram subsample every two metres along the feed pile to ensure that the samples represent the entire batch. They mix the subsamples thoroughly and take a total sample, which is then sealed in a clean, airtight container. This procedure ensures high accuracy and representativeness of the sample and reduces the risk of errors in the subsequent analysis.

The samples obtained must reflect all relevant properties of the feed.

SAMPLE COMMINUTION ENSURES HOMOGENEITY

Following sampling, sample comminution is essential for a high-quality analysis result. It ensures that the sample taken is homogenised and that all components of the feed are represented in the analysis. Appropriately optimised comminution ensures that all components, whether coarse or fine, are evenly distributed in the sample. The particle size distribution is therefore changed in such a way that a homogeneous mixture is created. It is particularly important to reduce the upper particle size in order to ensure a uniform particle size and compatibility with subsequent analysis methods. The desired particle size therefore depends on the requirements of the planned analysis and should be uniform in order to enable precise measured values. The analysis is also supported by the fact that the specific surface area of the particles is increased in the course of sample comminution, which improves solubility and reactivity in chemical analyses. Proper comminution also breaks down adhesions, as the individual components of composite materials are exposed and can be analysed individually. In order to achieve the best possible result, the use of modern high-performance mills is recommended. They grind samples efficiently and homogeneously without changing the material properties. A good example of this is the FRITSCH Cutting Mill P-29, which is specially designed for the comminution of small sample quantities for animal feed analysis with low moisture loss.

Crushing of animal feed in a knife mill.

To ensure the quality of the measurement, the grinding equipment used should be cleaned regularly to prevent contamination by residues from other samples. A completely cleaned and calibrated grinder should therefore always be used, which is sterilised for each new sample. The design of the device used can help with this. For example, the clean design of the FRITSCH cutting mill P-19 enables simple and contamination-safe cleaning.

Pellets ground in a cutting mill.

When using high-tech devices, care should also be taken to ensure that the sample is crushed as gently as possible or at a moderate speed so that the temperature remains low. This is because if the sample is heated too much during comminution, this can lead to the loss of volatile compounds or the alteration of certain ingredients. This is exactly what instruments like the P-14 from FRITSCH prevent. With its smart combination of impact and shear action, the rotor mill, which is designed for temperature-sensitive samples, ensures fast and gentle comminution - even materials previously embrittled by liquid nitrogen.

SAMPLE DIVISION INTO REPRESENTATIVE SHARES IS CRUCIAL

The comminuted total sample is usually too large for direct analysis and must therefore be divided. A representative and manageable partial sample is obtained for analysis as part of the so-called sample division. It must be ensured that each sub-sample has the same composition as the total sample. The sample division must therefore prevent specific components from being favoured or excluded. In addition, the individual components are evenly distributed during the process, which reduces systematic deviations and ultimately minimises errors. Depending on the material and process specifications, various techniques such as the riffle divider or the cone and quartering method can be used for sample division. Automated sample dividers such as FRITSCH’s rotary cone sample divider L-27 are recommended as they enable particularly precise and reproducible division of the samples. This model allows up to 30 units at a rate of 3,000 division steps per minute and achieves a division accuracy of 99.99 percent. Designed with food-safe materials, it ensures easy cleaning, thanks to its detachable dividing head, making it especially suitable for applications with strict hygiene requirements. Using modern technology, identical subsamples can be obtained, each of which has the same distribution of components as the original total sample. In order not to contaminate the sample and avoid material loss, a clean working environment and careful handling are also crucial in this sub-step.

Crushed beans in a rotor mill.

AVOID TYPICAL SAMPLE PREPARATION ERRORS

Errors often occur during sample preparation, which distort the entire analysis and lead to inaccurate results.  For example, if a sample is only taken from one layer or only a partial area of the feed, it is not representative. This can lead to the analysis not reflecting the entire feed batch. Further problems arise if tools or containers are not cleaned properly, which can lead to residues contaminating the actual sample. Storage can also be a pitfall, for example if samples are stored at too high a temperature or in humid environments. This sometimes leads to moisture absorption or chemical reactions, which changes the composition of the sample. In addition to such systematic errors, random errors can also occur, for example in the form of fluctuations caused by uncontrolled variables that are statistically distributed. In order to minimise these sources of error, a careful and methodical approach to sampling, comminution, division and storage is essential. It is therefore particularly important to standardise methods by applying consistent procedures for sampling and sample preparation. It is also essential that equipment and procedures are regularly checked for accuracy and precision as part of quality controls. Equally important is adequate staff training. It ensures that all employees understand the importance of sample preparation and implement it correctly.

CONCLUSION

At a time when the demands on the quality and safety of animal feed are constantly increasing, the importance of sample preparation should not be underestimated. It is the foundation of every analysis and is decisive for the validity of the results. By consistently implementing proven procedures and using modern technologies, the animal feed industry can successfully meet these challenges and continue to provide high-quality products for the market.

Adequate sample division and sample comminution are not just supporting steps, but fundamental prerequisites for scientifically sound, concrete and reproducible analysis results in the animal feed industry. They ensure that the measurements reflect the actual composition of the entire batch and thus provide reliable data for quality control, product development and compliance with legal regulations. Investment in modern sample preparation technologies and staff training is therefore essential for the success and credibility of a company in the animal feed industry.