Advances in steam-flaking grain sorghum and predicting starch availability for cattle
Smith, Kenneth Jackson
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The use of grain sorghum as a feedstuff for feedlot and dairy cattle is a common practice in the southwestern United States. A decline in the use of grain sorghum has been noted over the past decade. This decline has occurred because of the high degree of variability in grain sorghum as compared to corn in physical and chemical properties. Therefore, it was the intent of this research to determine the exact cost of steam flaking corn and sorghum, to determine the role of cultivar on utilization of sorghum grain by ruminants, and to develop indices and equations which determine flake quality and starch availability utilizing numerous whole grain factors, flake measurements, and starch texture data. US No 2 corn and US No. 2 grain sorghum were steamed exactly 20, 30, or 40 minutes and then flaked utilizing a laboratory steam flaker. Corn required more (P<.05) electrical energy and processing time for steam-flaking as compared to sorghum grain after 20 and 40 minutes of steaming time. Flake durability was greatest in corn across all cooking times and was diflferent (P<.05) from grain sorghum. The effect of grain sorghum cultivar on flake quality and utilization by ruminants was determined. Grains consisted of waxy, heterowaxy and normal endosperm type grain sorghum cultivars. The commercial cultivars utilized in this study represent the major genetics utilized by the seed industry today. Differences (P <.05) in digestibility were found across grain sorghum cultivars after 2, 4, 8,16,24,48 and 96 hours of incubation time in rumen fluid. Differences (P<.05) in starch availability and starch solubility after 8 h of incubation time in rumen fluid were found among grain sorghum cultivars. Time and energy required to process 22.72 kg were different (P<.05) across grain sorghum cultivars. Use of raw grain parameters along with starch texture analysis was utilized to develop an index to predict flake quality and equations to determine starch availability. The starch solubility technique which was developed in this work may be a better predictor of starch utilization than the present enzyme susceptible starch technique utilized by the industry today Starch solubility was positivley correlated to enzyme susceptible starch, however, it was not significant (P=.1361). Starch solubility was positivley correlated to 8 h dry matter digestibility and was significant (P=.0611). This indicates that starch solubility may predict utilization better than the standard enzyme susceptible starch method. Results indicate that grain sorghum processes more efficiently than corn when steam-flaking for cattle cultivar of grain sorghum has an effect on nutrient utilization and flake characteristics. These data indicate that regression equations can be used to predict flake quality and starch availability.