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When it comes to size reduction of principal feed ingredients, recent practice has been to use hammermills as the main grinding machines.
This wasn’t always the case. In the early days of compound feed milling, when raw materials were homegrown and power sources were either wind or water, the effort needed to grind or flake cereals into a form where animal uptake was optimized dictated that roller milling was a more economic and popular means of size reduction.