Particle size distribution of hammer-milled maize and soybean meal, its nutrient composition and in vitro digestion characteristics

F. Lyu, A.F.B. van der Poel, W.H. Hendriks, M. Thomas*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The mean particle size of ground grains influences both pig growth performance and gastric health although this effect is not consistent and the underlying reasons are not fully understood. The inhomogeneous nutrient content distribution in particles of different sizes and the characteristics of particles may be reasons for inconsistent findings. The objective of the present study was to determine the nutrient content and physical characteristics of individual size fractions of hammer-milled maize and soybean meal (SBM), and to relate it to in vitro digestibility. Maize and SBM were hammer-milled over a 6- and 2-mm size screen, respectively, and were sieved into seven fractions. Particle characteristics of the hammer-milled material were determined by dry sieving, wet sieving and image analysis methods; the nutrient composition including dry matter, ash, crude fibre (CF), crude fat (CFat), crude protein (CP), starch and in vitro digestibility of organic matter (OM), CP (SBM) and starch (maize) were measured and nitrogen-free-extract was calculated. The results show that the nutrient composition differed among fractions of ground maize and SBM (P < 0.001). A large difference in starch levels (754.2 vs 578.9 g/kg) of maize was observed between the various sieve size fractions whereas the CP content of SBM increased with larger sieve sizes. The in vitro digestibility of OM and CP was different (P < 0.001) among the various particle size fractions for both ingredients. However, the in vitro digestibility of starch did not differ between each size fraction in maize (P = 0.060). The regression models relating the nutrient composition and in vitro digestibility show that the digestibility of OM was positively related to the starch level (P < 0.001). As for SBM, CF (negatively) and CFat (positively) were correlated with OM digestibility (P < 0.001); ash and CF had a negative effect on the digestibility of CP, though CFat had a positive relation with the CP digestibility (P < 0.05). Using image analysis, the OM digestibility of different fractions of maize and SBM could be related to the projected perimeter (R2 = 0.933) and solidity (R2 = 0.704) of particles in a linear model. The presented data show that the nutrient composition and physical characteristics of materials among various size fractions of hammer-milled maize and SBM differ and may explain pig growth performance differences observed in commercial production.

Original languageEnglish
Article number115095
JournalAnimal Feed Science and Technology
Volume281
DOIs
Publication statusPublished - Nov 2021

Keywords

  • In vitro digestibility
  • Maize
  • Nutrient contents
  • Particle size
  • Pig
  • Soybean meal

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