Digestibility of corn distiller’s dried grains with solubles in practical feeds with phytase and xylanase treatment fed to Nile tilapia

Authors: Welker, Thomas; Sealey, Wendy; TAN, RONNIE - Us Grains Council

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2023
Publication Date: 11/2/2023
Citation: Welker, T.L., Sealey, W.M., Tan, R. 2023. Digestibility of corn distiller’s dried grains with solubles in practical feeds with phytase and xylanase treatment fed to Nile tilapia. North American Journal of Aquaculture. 86(1): 154-162. https://doi.org/10.1002/naaq.10325.
DOI: https://doi.org/10.1002/naaq.10325

Interpretive Summary: Economical alternatives for partial or full replacement of fishmeal and other costly protein sources have been at the forefront of feed research and formulation for many years. For numerous omnivorous fish species, such as tilapia, soybean meal (SBM) has been a readily available and more affordable choice. However, the price of SBM has seen a 50% increase in price (USD/Metric Ton) over the last 5 years (as of this writing). Therefore, identification of other alternative protein sources with acceptable nutritional profiles that are economically priced and highly palatable and digestible to tilapia have taken renewed importance. Distiller’s dried grains with solubles (DDGS), a byproduct of ethanol production from corn and other cereal grains, is one such protein source which has a reasonably complete nutritional profile and competitively priced (on a per protein unit basis) relative to other conventional alternative protein sources, such as SBM. The use of corn DDGS in feed for tilapia is limited primarily by high crude fiber and, to a lesser extent, low levels of essential amino acids (especially lysine and methionine). Corn DDGS also has a considerable level of phytic acid making a significant portion of dietary phosphorus unavailable to tilapia. Suggested dietary limits for DDGS are approximately 30% of diet for tilapia, depending on the exact formulation. Although corn DDGS has been around for some time, digestibility of major nutrients in DDGS has not been adequately evaluated for tilapia. In this study, we determined digestibility of the major nutrients (dry matter, crude protein, crude fat, ash, digestible energy, and phosphorus) in corn DDGS supplied at 30% of diet. Diets (reference and DDGS) were extruded, dried, and top-coated with phytase and xylanase enzymes. Compared to the reference diet, apparent digestibility of nutrients in DDGS was better or similar (crude fat, ash, crude protein, phosphorus) to the reference diet or was worse and improved to reference diet values after treatment with xylanase + phytase (dry matter, digestible energy). Corn DDGS is a highly digestible source of protein for tilapia, but for other nutrients, enzyme treatment may be required to be adequately utilized.

Technical Abstract: Apparent digestibility coefficients (ADC) for the major proximate nutrients (dry matter, crude protein, crude fat, ash, digestible energy, and phosphorus) were determined in corn distiller’s dried grains with solubles (DDGS) for Nile tilapia. Practical, commercial-type feed was formulated and processed with DDGS supplied at 30% as w:w substitution (DDGS diet) of the reference diet (Ref). After drying, Ref and DDGS diets were top-coated with phytase (3310 FTU/kg) + xylanase (7665 BXU/kg) enzymes (Ref+ and DDGS+) and compared to their untreated dietary counterparts. Digestibility of crude protein was similar among diets and unaffected by enzyme treatment. For dry matter and digestible energy, ADC values were significantly lower for the DDGS diet, but enzyme addition improved digestibility to that of the Ref diets. Apparent digestibility for crude fat and ash was significantly better for the DDGS feed with ash digestibility improved after treatment with xylanase + phytase for both Ref+ and DDGS+. For phosphorus, digestibility was similar among the Ref, Ref+, and DDGS diets, but with enzyme treatment, the phosphorus ADC increased significantly in DDGS+. Results of this digestibility trial show that corn DDGS is a highly digestible protein source for use in feeds of Nile tilapia at 30% of diet. Generally, apparent digestibility of proximate nutrients was either better or similar in DDGS when compared to the reference diet and could be further improved with addition of xylanase + phytase.