effect of drying temperature on the nutritional quality of New Zealand-grown maize for growing rats

The effect of drying temperature (ambient, 58, 80, 110 °C) on the nutritional quality of grain from two New Zealand maize hybrids (P3476, P3730) grown at two locations (Bay of Plenty, Waikato) was studied in growing rats, and the results of the biological evaluation were compared with the physical properties of the grain. Biological evaluation was carried out using 96 rats, with six rats for each of 16 hybrid x location x drying temperature treatments (three rats per analytical replicate). The experimental diets consisted of 94.5% ground grain supplemented with vitamin and salt mixes. The diets were offered at 15 g day-1 over a 5 day balance period. During the balance period, food intake was recorded and total faeces and urine were collected. The faeces and urine from the three rats of each replicate were pooled, and these samples, together with the diets, were analysed for total nitrogen (N) and gross energy. Dietary intake, faecal and urinary output, nutrient balance and nutrient digestibility and metabolisability were calculated for both N and energy. Before drying, the Waikato grain samples had a higher bulk density and the P3476 samples had a greater hardness. Breakage susceptibility for all samples increased with drying temperature. There were no statistically significant effects of drying temperature on the biological indicators used to assess nutritional quality, despite differences in the physical properties of the grain. There were several significant hybrid x location interactions that could be attributed to the P3730 x Bay of Plenty sample, and these interactions gave significant main effects. The findings suggested that significant savings in drying costs and enhanced productivity from the drying plant could be obtained by the feed grain industry, without compromising the nutritional value of the grain, by increasing the grain drying temperature.