Influence of processing variables during micronization of wheat on starch structure and subsequent performance and digestibility in weaned piglets fed wheat-based diets

Physical and nutritional characteristics of wheat following micronization were determined in three experiments, each based on four treatments with four gilts and four entire males (from 10 to 27 kg liveweight) per treatment all using the same batch of wheat, designed to investigate the effect of temperatures (different heating time, Trials 1 and 2) and preconditioning (steeping the grains for different lengths of time) prior to different micronization temperatures (Trial 3). Micronization of wheat reduced crystallinity, as detected through X-ray diffractogram analysis, and increased gelatinized starch and viscosity in vitro particularly when preconditioned. Coefficients of total tract apparent digestibilities (CTTAD) of dry matter (DM), gross energy (GE) and nitrogen (N) of diets containing wheat were not significantly different between treatments (Trial 1) neither was daily liveweight gain (DLWG). Diets containing raw wheat had significantly better (P=0.013) feed conversion ratio (FCR). Similar responses were obtained in Trial 2 suggesting limited effect of storage time prior to micronization. The influence of preconditioning (2 and 12 h steeping time) followed by low and high cook conditions was examined in Trial 3. Significant improvements for the shorter versus longer steeping time for DLWG (536 versus 484 g per day, P=0.007), feed intake (FI, 796 versus 735 g DM per day, P<0.001), CTTAD for DM (0.838 versus 0.812, P=0.006) and GE (0.828 versus 0.802, P=0.010) were observed, while interaction of steeping time×temperature was significant for FCR (P=0.029). No effect of heating time was observed. There were no correlations between animal responses within individual trials and wheat starch crystallinity or viscosity (in vitro assessments). In conclusion, the addition of wheat micronized under different conditions did not improve piglet performance although pre-conditioning did have an effect.