Reduction of whole grain to a smaller particle size will improve feed efficiency. By reducing particle size, the surface area is increased. This allows the particle surface to have greater contact with digestive enzymes in the intestinal tract. When particle size is reduced from 1,000 microns to 400 microns, digestibility is increased by an average of 5 to 6%. The average particle size of most ground feeds is approximately 1,100 microns, whereas the desired size to attain optimum digestibility is between 650 and 750 microns. Reducing particle size below 650 microns increases digesti-bility but it also increases the cost of grinding and reduces the output of the mill (Table 18). The excretion of undigested nutrients is therefore reduced when the particle size is smaller. Segregation or the separation of feed ingredients can also be minimized by grinding the grain to the same particle size as that of the protein source (approximately 700-750 microns). Incidences of stomach ulcers are, however, higher when feed is ground too fine. Management problems can occur when feeding diets that are too finely ground (e.g., bridging).
| Table 18. Effect of Grain Particle Size on Mill Energy Costs and Mill Production Capacity. | ||||
|---|---|---|---|---|
| Item | Grain Particle Size, Microns | |||
| 1000 | 800 | 600 | 400 | |
| Milling energy, kilowatt hours/ton | 2.42 | 2.78 | 3.46 | 7.35 |
| Milling production, tons/hr | 3* | 3 | 2.85 | 1.43 |
| * Milling production was limited by capacity of exit auger. | ||||