Abstract: The physical properties including diameter, length, hardness, bulk density, powder content and PDI (Pellet Durability Index) were measured for pig pellet feeds at different growth stages from a local feed mill. The results were classified and analyzed statistically referring to related standards. The results showed that the diameter was 2.87~3.94 mm with significant differences between each other(P<0.05) and increased with rise of pig age, it was the largest for sow feed and smallest for small pig feed. The particle length was 8.62~11.94 mm, it was the largest for large pig feed and the smallest for small pig feed. The length-diameter ratio was too high. The pellet hardness was 3.86~6.47 kg, it was the highest for large pig feed and the lowest for small pig feed. Hardness of small and medium pig feed was significantly lower than that of large pig feed and sow feed(P<0.05). Only small pig feed met hardness requirement. The bulk density was 576.7~614.6 g/L, which showed significant differences between each other and changed with the same trend of diameter. It was the highest for sow feed and the lowest for small pig feed. The powder content of small pig feed was the highest and only the difference between small pig feed and large pig feed was significant(P<0.05). PDI was the highest for large pig feed and the lowest for small pig feed. All feeds met related standards for powder content and PDI. Therefore, we suggest that feed manufacturers should pay attention to physical indices control by regulation of formula and processing parameters to improve physical quality of pellet feed.

Key words: pellet feed, diameter, length, hardness, bulk density, powder content, PDI