Location: Small Grains and Potato Germplasm Research
Project Number: 2050-10600-001-011-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Oct 1, 2024
End Date: Jan 31, 2026
Objective:
1. To formulate nutritionally complete diets specific to rainbow trout using normal red sorghum and waxy red and white sorghum as the primary carbohydrate sources, along with a control wheat-based diet.
2. Grind normal sorghum, waxy sorghums and wheat using a 0.84 mm hammermill screen and determine the associated energy costs and mixing uniformity of the final diets.
3. Produce floating rainbow trout feed using a single screw pilot-scale extruder and determine the optimal processing parameters necessary for a high-quality feed and to study the impact of normal and waxy sorghums on thermal and mechanical energy use during processing, as compared to wheat based diets.
4. Analyze the physico-chemical characteristics of raw materials and the physical quality of aquatic feed, and to determine the relationship between raw material functionality, processing, the different starch ratios present in waxy sorghums versus normal sorghum, and final product properties.
5. Conduct in vivo nutrition/ growth trials along with fecal stability analyses with rainbow trout to validate the use of normal sorghum and waxy sorghums in rainbow trout diets and determine their viability as the primary carbohydrate source in the complete diet, as compared to a wheat-based diet.
Approach:
While sorghum is essential to U.S. agriculture, there is a need to ensure farmers maintain and expand sorghum acreage. To be successful, sorghum must not only remain profitable though current market outlets but through the development of new markets. This aligns with the need for novel ingredient sources for fish feed. The aquafeed industry is in a period of increasing use of alternative ingredients and has become progressively dependent on conventional terrestrial ingredients, such as those from grains. For sorghum, entering the aquafeed market will require efforts similar to those already accomplished for other terrestrial ingredients. Waxy sorghum has special starch properties compared with normal sorghum. The term “waxy sorghum” signifies that a sorghum contains essentially amylopectin in its endosperm starch. Amylose and amylopectin are the two polymer molecules that constitute 99% of the weight of starch. The physical properties of starches when heated with water depend in large measure on their amylose content. In general, amylose promotes the gelling and film-forming properties of a starch. Amylopectin, on the other hand, increases the thickening power of starch and promotes clarity of starch pastes and gels. In general, digestibility of starch is negatively correlated with the amylose content. Waxy starch, which contains essentially no amylose, is more digestible than normal starch. Currently, research on amylose and amylopectin levels in starch indicate that amylose inhibits starch digestion, with waxy sorghum having more complete starch digestion and therefore performs better in poultry and swine diets. However, poultry and swine feed are primarily produced by pellet-milling, whereas aquatic feed is produced through extrusion. The high levels of mechanical shear and energy during processing will, in theory, increase the digestibility of the feed. The aim of this study is to determine the effects of extrusion processing on the digestibility of sorghum-based and waxy-sorghum based rainbow trout feeds.