How to Choose a TMR Mixer Size by Herd Size

Choose mixer size from the actual volume of one batch, not herd size alone. Calculate daily as-fed ration weight, divide it by the number of batches, convert batch weight to volume using measured ration density, and then check the manufacturer's recommended working fill range.

Reviewed by Anlan MachineryUpdated August 2026

Short answerChoose mixer size from the actual volume of one batch, not herd size alone. Calculate daily as-fed ration weight, divide it by the number of batches, convert batch weight to volume using measured ration density, and then check the manufacturer's recommended working fill range.

Why herd size alone is not enough

Two farms with the same number of cattle can need different mixer sizes. Ration moisture, forage length, bulk density, feeding frequency and the number of groups all change the volume handled in one batch. A useful recommendation therefore starts with the farm's real ration and operating schedule.

Four-step sizing method

1. Calculate total daily as-fed weight

Multiply the number of animals in each feeding group by the as-fed ration per head. Add the groups that will be prepared together. Use as-fed weight rather than dry-matter intake because the mixer physically handles the wet ration.

2. Divide by the planned number of batches

If the full daily ration is prepared in two loads, divide the daily as-fed weight by two. If different animal groups receive different formulas, calculate each batch separately and size for the largest normal batch.

3. Convert batch weight to actual volume

Measure the bulk density of the mixed ration whenever possible. Divide batch weight in kilograms by bulk density in kilograms per cubic metre. Light, long-fiber rations occupy more volume than dense, high-moisture rations of the same weight.

Illustrative calculation120 cattle x 35 kg as-fed ration = 4,200 kg per day. With two equal batches, each batch is 2,100 kg. If the measured ration density is 320 kg/m3, the actual batch volume is approximately 6.56 m3. The final nominal mixer size must still respect the selected manufacturer's recommended working fill range.

4. Check operating constraints

Never exceed the documented working load.
Allow enough mixing space for material circulation.
Check loading height, doorway height and feed-alley width.
Match electric motor or tractor PTO requirements.
Confirm the discharge side and unloading clearance.

Common sizing mistakes

Using cattle count without ration weight.
Using dry-matter intake instead of as-fed intake.
Ignoring separate recipes for different groups.
Assuming every cubic metre holds the same feed weight.
Selecting nominal volume without checking usable working capacity.

Which mixer type should you compare next?

A stationary mixer suits a centralized feed kitchen. A self-propelled mixer can combine mixing and distribution in restricted routes. A tractor-pulled wagon is practical where a compatible tractor and sufficient route clearance are available.