Feed Mixing Uniformity Test – Part 1

When formulating a diet, the ultimate goal of nutritionists is to match nutrient supply with the nutrient requirements of animals. This will ensure that an animal receives all of the nutrients in the right proportion on a daily basis. To achieve the goal, proper feed manufacturing steps should be practiced carefully. Producing high-quality feed starts with receiving, grinding, mixing, and batching of ingredients. A proper mixing procedure should be followed to produce a homogenous mixture where nutrients and medications are uniformly distributed. Having a uniform final mixture is important for optimal animal health and performance and to minimize food safety hazards related to nutrient toxicity. Furthermore, if the feed is to be further processed (to make a pellet or crumble form), an excellent mixture uniformity is necessary. The homogeneity of the final product is assessed using a procedure called the feed mixing uniformity test.

Feed uniformity testing is an important aspect of feed manufacturing that assesses the level of one or more tracers (nutrients) in a pre-established number of feed samples in a batch of feed to determine the feed homogeneity. Although there are some variations between samples of a batch, an ideal mixture is one with minimal variation in the composition of its samples. The feed uniformity test can help ensure the quality of the feed, reduce waste, increase efficiency, and ensure regulatory compliance. By assessing the uniformity of the feed, producers can determine if the ingredients are being mixed properly and if there are any variations that could affect the nutritional value of the feed. Consistent uniformity is essential for animal health, growth, and performance. Feeding a uniform feed ensures animals receive a balanced amount of nutrients to minimize the environmental footprint. Many regulatory bodies also require feed uniformity testing to ensure that the feed produced meets specific standards. By conducting regular testing, producers can ensure that their feed meets the required standards, avoiding regulatory issues and associated costs.

Mixing uniformity test procedure

The feed mixing uniformity test evaluates the degree of uniformity in the feed mix. To perform this test, samples of feed mix are collected from various parts within the mixer and analyzed for nutrient uniformity. The test result is expressed as a coefficient of variation (CV), which indicates the degree of variation in the mix. The following steps should be followed to evaluate a feed mixture uniformity.

  1. Sampling procedure

The sampling method depends on the mixer type (vertical and horizontal mixer). To take feed samples from a vertical mixer, take 10 equally sized samples (between 100 and 500 grams for dry feeds) from a single batch and have it analyzed for tracer(s) content. The sampling spots should represent the full batch. While the system is running, take the samples at even and predetermined time intervals (for example, every 10 seconds) at or as close to the mixer discharge as possible. Horizontal mixers are usually accessible from the top. To take feed samples from a horizontal mixer, use a grain probe to take samples from 10 different locations in the mixer. Read the Tool of the Month article in this newsletter to learn more about using grain probes!

  1. Choosing tracer(s)

To choose the right tracer, consider the following criteria. 

  1. The selected tracer(s) should come from a single ingredient source to avoid masking non-uniformity. 
  2. The method to determine the level of the tracer should be highly reproducible with a low variation. The analytical variability for lab methods should be less than the target CV for the mixer.
  3. The tracer also should have sufficient particles per gram to ensure the marker can be detected when the sample is obtained from the mixer.

Salt (sodium and/or chloride), synthetic amino acids (lysine, methionine), and trace minerals (zinc, copper, manganese) are suitable tracers for conducting the test.

  1. Analyzing the samples for tracer(s)

The feed samples should be sent to a feed analysis lab and analyzed for the tracer content. Alternatively, an on-farm test can be conducted to quantify the tracer (for example, chloride) concentrations in feed samples. I will introduce an on-farm test method in our next newsletter issue. Stay tuned!

  1. Calculating the Coefficient of Variation

Homogeneity is obtained by calculating the CV of the tracer content in the samples using the following formulas:

Interpretation of results

Mixer tests are interpreted based on CV ranges for the tracer content in feed samples. Herrman and Behnke (1994) categorized a CV of less than 10% as excellent, 10 to 15% as good, 15 to 20% as fair, and greater than 20% as poor. Guide to Feed Mixing protocol from the University of California, Davis suggests a 5% CV as the industry standard for most ingredients. A CV = 5% means that the distribution of the nutrient (tracer) is between plus or minus 10% of the average intended dose. If the average intended dose of a nutrient (chloride level in the previous example) is 0.20 % and the CV is 5% then standard deviation (SD) of the nutrient is 0.01. Based on the Gauss curve (normal distribution rule), the nutrient dose of 95% of the mass of the batch falls within 2 SD (in this example 2 SD is 2 × 0.01 = 0.02) of the average dose. In the previous example, this would be 0.20±0.02, which creates a range from 0.18 to 0.22% of dietary chloride level. In plain language, an animal receives at least 95% of its formulated dietary allowances between 0.18 to 0.22% of the nutrient. The following standards are based on the Guidance Document Repository (GDR) of the Government of Canada.

ProductTarget CV (%) for the mixing uniformity
Dilute drug premixes*Less than 5%
Micro or macro premixes and supplementsLess than 10%
Complete feeds and total mixed rationsLess than 15%
*Dilute drug premix means a drug for veterinary use that results from mixing a drug premix (drug identification number (DIN) product) with feed ingredients so that the final product has an inclusion rate of at least 10 kg per ton (1%) of complete feed when used at the lowest approved dosage level of the drug.

In conclusion, a validation test for mixer performance should be periodically performed to ensure homogeneity is achieved. If not, corrective actions should be implemented, and their efficacy should be assessed. Stay tuned for the corrective actions in our next article!


Fahrenholz, A. C. 2019. Best practices: Mixing and sampling. Animal Feed Science and Technology. 250 51–52. (Link)

Herrman, T. 2001. Sampling: Procedures for Feed. MF-2036. Kansas State University Agricultural Experiment Station and Cooperative Extension Service Bulletin (Link

Herrman, T. and K. Behnke. 1994. Testing mixer performance. MF1172. Kansas State University Agricultural Experiment Station and Cooperative Extension Service Bulletin, Manhattan, KS: Kansas State University (Link)

Stark, Ch., and Saensukjaroenphon M. 2017. Testing Mixer Performance. Kansas State University. (Link

Zinn, R. A. 2020. A Guide to Feed Mixing. University of California, Davis. (Link)

About the author(s)

Research Associate at Poultry Innovation Partnership | + posts

2 Responses

  1. As always, practical information, explained simply but thoroughly.