Research has shown that grinding cereal grains in diets fed to pigs into smaller particle sizes improves growth performance. Feed ground to smaller particle sizes has more surface area on which digestive enzymes can work, so digestibility of energy and nutrients that are enzymatically digested may also improved. Generating specific data on energy and nutrient digestibility will help determine the optimal particle size for feed ingredients.
An experiment was conducted to determine the concentration of digestible and metabolizable energy and to measure the apparent (ATTD) and standardized total tract digestibility (STTD) of phosphorus by growing pigs fed diets containing corn that was ground to different particle sizes.
Experimental design
A total of 32 growing barrows with an average initial body weight of 22.8 kg were fed one of four experimental diets. All diets consisted of 97.5% corn. The corn in each diet was ground to a mean particle size of 338.5 μm, 485.0 μm, 676.5 μm, or 864.5 μm. All energy and phosphorus in the diets was supplied by corn.
Urine and fecal samples were collected and analyzed to determine the concentrations of digestible and metabolizable energy in each diet, as well as the apparent total tract digestibility (ATTD) of phosphorus. The standardized total tract digestibility of phosphorus was calculated by correcting the ATTD by the values for the basal endogenous losses of phosphorus.
Decreasing particle size increases energy digestibility
The apparent total tract digestibility of gross energy showed both a linear and quadratic decrease (P < 0.05) as corn particle size increased (Table 1). Concentrations of digestible and metabolizable energy also showed both a linear and quadratic decrease (P < 0.05) with increasing particle size. This was true both on an as-fed basis and on a dry matter basis.
Particle size has no effect on phosphorus digestibility
A linear decrease in percentage of phosphorus in the feces was observed as particle size increased (Table 2). However, no significant difference in apparent or standardized total tract digestibility of phosphorus was observed among experimental diets.
Key points
- Concentrations of digestible and metabolizable energy in corn increased as corn was ground to smaller particle sizes in the range of 338.5 μm to 864.5 μm.
- Particle size in the range of 338.5 μm to 864.5 μm had no effect on phosphorus digestibility.
- Feeding smaller particle sizes will result in the most efficient use of the energy in corn.
- As the particle size of corn is reduced, the risk of pigs developing gastric ulcers is increased, which needs to be taken into account when deciding on the particle size of corn.
Table 1. Concentration of digestible and metabolizable energy, and apparent total tract digestibility (ATTD) of energy in corn ground to different particle sizes
| Item | Corn | P-value | |||||
| 338.5 μm | 485.0 μm | 676.5 μm | 864.5 μm | Linear | Quadratic | ||
| ATTD of GE, % | 91.6 | 90.3 | 89.2 | 88.7 | < 0.01 | < 0.01 | |
| DE, kcal/kg | 3,547 | 3,492 | 3,441 | 3,402 | 0.01 | 0.01 | |
| DE, kcal/kg DM | 4,097 | 4,035 | 3,978 | 3,932 | 0.02 | 0.02 | |
| ME, kcal/kg | 3,432 | 3,371 | 3,346 | 3,311 | < 0.01 | < 0.01 | |
| ME, kcal/kg DM | 3,964 | 3,895 | 3,868 | 3,826 | < 0.01 | < 0.01 | |
Table 2. Effect of particle size on apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of P in corn
| Item | Corn | P-value | |||||
| 338.5 μm | 485.0 μm | 676.5 μm | 864.5 μm | Linear | Quadratic | ||
| P intake, g/d | 2.57 | 2.60 | 2.67 | 2.48 | 0.63 | 0.22 | |
| P in feces, % | 2.65 | 2.56 | 2.31 | 2.15 | < 0.01 | 0.91 | |
| P output, g/d | 1.81 | 1.79 | 1.84 | 1.71 | 0.49 | 0.44 | |
| Absorbed P, g/d | 0.76 | 0.81 | 0.83 | 0.77 | 0.92 | 0.69 | |
| ATTD of P, % | 29.62 | 30.99 | 31.15 | 31.26 | 0.67 | 0.81 | |
| STTD of P, % | 37.79 | 37.12 | 37.27 | 37.38 | 0.99 | 0.87 | |
This report is based on unpublished data by O. J. Rojas and H. H. Stein.