Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2014
Publication Date: 9/8/2014
Citation: Welker, T.L., Lim, C.E., Barrows, F., Liu, K. 2014. Use of distiller's dried grains with solubles (DDGS) in rainbow trout feeds. Animal Feed Science And Technology. 195:47-57.
Interpretive Summary: Fish meal (FM) is the primary protein source used in commercial rainbow trout diets. It is a complete protein source that is easily digested by trout. However, demand for FM has increased in recent years due to expansion and intensification of aquaculture production worldwide and in particular, Southeast Asia and China, and use of FM in feeds of terrestrial livestock species is also limiting the availability of FM for use in fish feeds. Global demand for food-fish is projected to increase markedly in the future, and with most natural fisheries stagnating or declining, food-fish aquaculture production is predicted to experience a 100% increase by 2020. This increased production will continue to place high demand on FM for use in fish feeds. In addition, profit margins for commercial aquaculture are often small with fish feed accounting for the majority (up to 60%) of the production costs. The price of FM has nearly tripled since 2000 and is projected to rise further in the future, which will increase the cost of trout feed. Therefore, trout producers and feed manufacturers have been searching for low-cost alternative protein sources with renewed interest. In recent years, increasing demand for ethanol as a fuel additive and decreasing dependency on fossil fuels have led to a dramatic increase in ethanol production from various cereal grains (corn, wheat, sorghum, rye, etc.). The majority of ethanol production in the United States is from corn using a dry-grind method, which produces the particulate coproduct known as distiller’s dried grains with solubles (DDGS). DDGS is currently readily available and competitively priced (on a per unit protein basis) relative to other conventional alternative protein sources, such as SBM. The protein content of DDGS is high enough (typically 25-45%, depending on the grain source) to be practically used as a protein source in trout diets; however, high 'ber content limits the level that can be incorporated into diet. DDGS is also deficient in a few EAA, but these deficiencies can largely be overcome through addition of EAA to fish feeds. As a fish feed ingredient, DDGS is lower in phosphate content relative to animal ingredients. However, approximately half of the phosphorus in DDGS is present as phytate. Phytate phosphorus is largely unavailable to trout. Methods have or are currently being developed to increase the nutritional value of DDGS for use in fish feeds. Moreover, the quality and nutritional composition can vary considerably between and within DDGS grain sources and between processing plants, further complicating incorporation of DDGS into trout diets. With a rapid increase in DDGS supply, there is a need to enhance the nutritional value and improve the nutritional consistency of DDGS for use in diets of rainbow trout and other fish species. The nutritional value and limitations to incorporation of DDGS in diets of rainbow trout will be addressed in this review.
Technical Abstract: Increasing price and reduced availability of fish meal have prompted feed manufacturers and aquaculture producers to search for sustainable and economical alternative protein sources. The majority of these have come from plants, and many, for example soybean meal, have been successfully incorporated into diets of rainbow trout and other fish species. Distiller’s dried grains with solubles (DDGS) is a co-product of the grain-based fuel ethanol industry. DDGS is moderately high in protein (typically around 30% or higher, depending on the source) and is readily available and competitively priced relative to other alternative protein sources. As with other plant protein sources, there are limits to the use of DDGS in fish feeds. DDGS is deficient or near-deficient in some essential amino acids (EAA), but these deficiencies can be overcome through addition of EAA. DDGS is also low in phosphorus and about half is present as phytate phosphorous (phytate P), which has limited bioavailability to trout. This is a concern for commercial hatcheries, because dietary phosphorus that cannot be utilized by trout is excreted, which can lead to eutrophication of receiving waters. Phosphorous utilization by trout fed DDGS-based diets can be improved by dietary application of phytase. In addition, high levels of fiber limit the incorporation of DDGS in diets of rainbow trout to approximately 10-20%. Fractionation of DDGS can reduce fiber and increase the relative protein concentration to produce a higher value product. Digestibility of these high protein fractionates is improved in trout, and higher dietary levels (up to 30%) are tolerated. The quality and nutritional composition can also vary considerably between and within DDGS grain sources and between processing plants, which further complicates incorporation of DDGS into trout diets. Production of high-value, high protein products through fractionation or other means may be needed to improve the nutritional value and consistency of DDGS for use in diets of rainbow trout.