Corn kernel hardness is an important agronomic trait that could be affected by environmental conditions and post-harvest practices such as drying and storage. This dissertation discuss current literature related to corn variability factors and original research showing the effects of two corn hybrids varying in endosperm hardness (average vs. hard) and three post-harvest drying temperatures (35, 80, and 120°C) on corn nutritional composition, geometric mean (dgw) and standard deviation (Sgw) of particle size, and pellet quality. Likewise, the effect of storage time on the parameters previously listed will be presented. The supplementation of diets containing these corn hybrids with an exogenous amylase was also evaluated, to investigate its effects on broiler live performance, organ development, nutrient digestibility and energy utilization.
In the first chapter, the literature presents an overview of factors that influence corn nutritional value with emphasis in kernel hardness, and feed manufacturing processes such as grain drying temperature and grinding. The second chapter describes the differences on corn nutritional composition among two corn hybrids dried at three temperatures, analyzed by different NIRS prediction models. The non-standardized spectra from whole grain and ground samples were obtained at two storage times (2 and 24 wk). It was concluded that endosperm hardness and drying temperatures influenced the nutritional value of corn. Likewise, storage time increased the estimated value of crude protein and reduced starch content in all treatments except for corn with average kernel hardness and dried at 120°C. In the third chapter the two corn hybrids dried at three temperatures were milled either in a roller mill or hammermill at different grinding settings. The effects of kernel hardness and drying temperatures on dgw and Sgw were studied. This evaluation was conducted in fresh corn (less than 2 wk of storage) and at 30 wk of storage. Results showed a larger dgw for corn with harder endosperm and dried at 120°C. This study also demonstrated that as storage time increase the dgw is reduced regardless of grinding method.
For chapter four, the supplementation with an exogenous amylase on broiler live performance, nutrient digestibility and energy utilization was investigated. For this study a factorial arrangement of two corn kernel hardness, three drying temperatures, and two amylase supplementation (0 vs. 133 g/ton) levels were considered. Two parallel studies were carried out in 96 floor pens and cages. Live performance results showed that at 40d the best FCR was observed when the average hardness kernels were dried at 120°C. Additionally, the supplementation with amylase improved FCR in 2 points, but only when feeding diets comprised by corn with average hardness.
Considering that there were no improvements when supplementing amylase for chickens fed hard kernel corn, and that corn dried at 120°C yielded larger dgw, a second experiment was conducted. The effects of hard kernel corn dried at two temperatures (35 vs. 120°C), ground at two particle sizes (coarse and fine), and three amylase inclusion levels (0, 133, and 266 g/ton) were evaluated on live performance, organ development, nutrient digestibility, and energy utilization. Results showed that high drying temperature depressed ileal starch digestibility, especially for young chicks. Feeding coarse corn did not improve live performance, but it promoted gizzard development. Finally, at 42d; FCR was improved when supplementing amylase at 266 g/ton.
The results obtained in these experiments suggested that endosperm hardness, and drying temperatures influenced corn nutritional composition, dgw and Sgw. Likewise, it affected broiler live performance, nutrient digestibility and energy utilization. Some improvements were observed on these parameters by adding an exogenous amylase in the feed. However, these factors were not independent and so must be manipulated strategically to improve corn nutritional value.