Premix Carriers

Formulating a good quality premix requires the correct choice of carrier for the application and the ingredients in the formula. Organic carriers are preferred for their “soft” nature, without being physically abrasive on vitamins.

For conventional premixes, the main source in Canada is Wheat middlings, a by-product of flour milling. Wheat middlings have an even distribution of particle size, ideal for providing optimal carrying capacity for vitamins. In the USA, the primary carrier used is Rice hulls, which has a slightly coarser consistency than wheat middlings. 

Figure 1. Left to right, Rice Hulls, Wheat Middlings, and Wheat Flour.

Final application is an important consideration in premix formulation and choice of carrier. For example, Aqua premixes require small particle sized carrier for early life stages, and so wheat flour is used for its fine particle size. Another important requirement for carriers is for Grain-free pet food, which excludes the use of wheat or Rice by-products. Pea Fiber is one solution for these premixes, with novel ingredients being introduced such as M-fiber, grown from Miscanthus grasses, are becoming more prevalent in the pet food industry. Although by-products are efficacious and cost-effective carriers, nutritive carriers such as probiotics and yeasts can also be used effectively and be beneficial in reducing number of micro bins needed at feed mills.

Figure 2. M-Fiber

Commonly used carriers for Water soluble applications include Whey, commonly used for Calf milk replacer premixes, and Citric acid, which has an additional benefit where acidity can protect against bacterial growth with water lines.


A diluent is used to improve flowability, adjust bulk density, and acts as a carrier to dense or granular minerals to improve homogeneity. The most commonly used diluent is calcium carbonate, which is available in coarse and fine grind size, and is an inexpensive addition that can provide benefits such as increased pH, flowability, and the ability to decrease premix bulk density. However, increasing proportion of a diluent such as calcium carbonate can have a negative impact on vitamin stability, as it can be physically abrasive on vitamins. Also, finer particles may segregate out and increase dustiness.

Figure 3. Calcium Carbonate, fine and coarse particle size.

Carrier proportions

Modifiying carrier proportions and types is required to ensure a good quality premix. The ideal particle size distribution of a premix is a bell-shaped curve, ideally matching the distribution of active particles. If the carrier has a large particle size, fine active particles will easily separate out, demonstrated in Figure 4.

Premixes consisting of trace minerals are typically on coarse calcium carbonate, as the dense particles “match” the range of particles seen in most trace mineral sources. For vitamin premixes, the ratio of organic carrier to diluent is chosen based on overall “room” for carrier and estimated bulk density. 

Another crucial impact of carrier proportions is to bulk density of a premix. Adjustments can be made to meet a feed mill’s needs, or for packaging limitations, for example, adjustments can be made for 25 kg of a premix “fit” in a bag where previously it was too bulky.

Figure 4. Comparison of Rice Hulls and Wheat Middlings with and without Calcium carbonate.

Nutritional Services can assess novel ingredients for use as premix carriers and are investigating further insights into premix quality based on ideal carrier proportions and inclusion.  

Figure 5. Good Particle size distribution of a premix
Figure 6. Poor particle Size distribution of a premix

Published on

20 June 2022


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