Evaluation of a modified method to measure total starch in animal feeds

The AOAC method 996.11 (AOAC, 2005) has been recognized as an accurate, repeatable, and efficient method to measure total starch in animal feeds. However, analyzing starch using the AOAC method can be expensive and associated with technical challenges. The objectives of this study were to determine if an alternative modified starch method (MAOAC) could be more economical and minimize technical challenges associated with the AOAC method. Modification of the AOAC method, 996.11 (AOAC, 2005) was done by combining the AOAC method with the acetate buffer method of Hall (2009) and introducing alpha-amylase (1162 liquefon units/assay) and amyloglucosidase (400 units/assay) from different sources (ANKOM Technology Inc., Macedon, NY and Sigma-Aldrich Inc., St. Louis, MO). Dried rumen and fecal samples, alfalfa hay, dried distillers grains with solubles, corn silage, total mixed ration (TMR), concentrate mixture, ground corn, and pure corn starch were analyzed using the AOAC and MAOAC methods. Two technicians performed two runs of each method and all samples were analyzed in duplicate within each run. The average starch concentration for 9 samples was not affected by method (AOAC method = 298.7 ± 1.84; MAOAC = 298.0 ± 1.39 g/kg; P = 0.49), technician (technician I = 297.8 ± 12.8 g/kg; technician II = 299.0 ± 19.6 g/kg; P = 0.24), or run (run I = 298.4 ± 15.3 g/kg; run II = 298.1 ± 17.0 g/kg; P = 0.59). The average time spent to analyze 18 assays was approximately 3 h for both methods. Average chemical cost per assay with the MAOAC method was $0.88 compared with $3.41 for the AOAC method. There was a 79% decrease in water consumption for the samples containing >100 g/kg starch with the MAOAC method compared with the AOAC method. The MAOAC starch assay could be considered a cost-effective, more environmentally friendly, and less technically difficult method compared with the AOAC starch method.