Animal nutrition science is built on milligrams and micrograms. The trace minerals and vitamins added to a tonne of compound feed often make up only a few hundred grams of the total weight, sometimes as little as 50 grams. For elements such as selenium, cobalt or iodine, the gap between the needed dose and the toxic dose is very thin.
This is where the key measure of a feed mill's or premix producer's quality comes in: mixing homogeneity. If one pellet an animal eats does not have the same active ingredient content as another, one animal in the herd may get an overdose while another suffers a micronutrient deficiency. In this article we cover the concept of the homogeneity coefficient (CV) and the CV < 5% standard that MCB Vital targets at its Konya facility.
What Is the Coefficient of Variation (CV) and How Is It Calculated?
The coefficient of variation is found by dividing the standard deviation by the arithmetic mean and multiplying by 100: CV = (s / x̄) × 100.
For a homogeneity test in the feed industry, samples are taken from the mixer or from different points on the production line (at least 10 points). The tracer in the samples (usually a trace mineral or salt) is analysed in the laboratory. The generally accepted assessment is as follows:
- CV > 15% (unacceptable): The mixer design is faulty, mixing time is too short or there is electrostatic segregation. This creates yield imbalance and a risk of poisoning in the herd.
- 10-15% (poor): Tolerable in forage mixes, but inadequate for premix and concentrate feed production.
- 5-10% (good): The average quality level seen in conventional feed mills.
- CV < 5% (excellent): A superior quality level that can be reached with advanced twin-shaft paddle mixer technology, micronised carrier optimisation and electrostatic control.
Risks of Non-Homogeneous Mixes in the Herd
Too much or too little of a micronutrient causes different problems:
- Selenium (about 0.30 ppm): Excess causes blindness, hoof loss and respiratory paralysis; deficiency causes white muscle disease and weaker immunity.
- Cobalt (about 0.50 ppm): Excess causes loss of appetite, anaemia and liver damage; deficiency impairs vitamin B12 synthesis and leads to weight loss.
- Iodine (about 1.0 ppm): Excess causes mucosal irritation and goitre; deficiency causes hypothyroidism, stillbirth and hair loss.
- Vitamin D3 (2,000-4,000 IU/kg): Excess causes calcification in the kidneys and tissues; deficiency causes rickets and shell breakage.
- Copper (10-15 ppm in sheep): Sheep are very sensitive to copper. Excess can end in haemolysis and death; deficiency causes poor wool and lower enzyme activity.
Segregation Physics and Carrier Selection
It is not enough for a premix to mix homogeneously in the mixer; it must also keep its homogeneity during bagging, transport to silos and dosing. Segregation has 3 main causes:
- Particle size difference: Coarse particles stay on top while fine particles sink. This is why trace components are micronised to a range of 150-250 microns.
- Density difference: Heavy inorganic minerals such as zinc oxide can separate from light organic carriers such as bran. Modified carriers and mineral oil spraying technology provide binding.
- Electrostatic charge: Dry friction makes particles stick to the mixer wall. Anti-static carrier matrices should be used.
Frequently Asked Questions
How can we test the homogeneity of the mixer at our mill?
MCB Vital's technical service visits your mill and takes 10 samples from different times along the mixer discharge line. Through tracer microelement analysis, your mill's CV value and ideal mixing time are reported.
Does mixing for longer improve homogeneity?
No. Mixing beyond the optimal time (usually 90-150 seconds in paddle mixers) causes "de-mixing". Static electricity rises and mixing quality deteriorates.
Why is homogeneity especially important in premix?
Active ingredients in premix are present at very low doses. Even a small distribution error can cause one animal to get too much and another too little.
