Impacts of alfalfa nutrient concentration on pellet physical attribution, growth performance, metabolism and nutritional quality of rainbow trout, Oncorhynchus mykiss

Authors: BLAUFUSS, PATRICK - University Of Wisconsin; CHEN, HU - University Of Wisconsin; DENG, DONG-FANG - University Of Wisconsin; CASU, FABIO - South Carolina Department Of Natural Resources; Kraco, Emma; Shepherd, Brian; Sealey, Wendy; DIGMAN, MATTHEW - University Of Wisconsin; Samac, Deborah - Debby

Submitted to: Animal Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Traditionally, fishmeal has been the preferred protein and lipid source in aquaculture feeds due to its optimal nutritional profile. Nevertheless, limited fishmeal availability has resulted in rising prices and instability. Extensive efforts have been made to explore alternative ingredients for aquatic feed production. One such potential alternative ingredient is alfalfa nutrient concentrate. Alfalfa nutrient concentrate is a protein source and phytonutrient supplement that enhances growth, meat and egg quality, and health in poultry and swine. To investigate the suitability of alfalfa nutrient concentrate inclusion in aquatic feeds, USDA, ARS researchers at Bozeman Fish Technology Center collaborated with researchers at the University of Wisconsin, Milwaukee to examine effects on feed pellet quality, feed intake, and trout growth and health. Results from this comprehensive assessment indicate that alfalfa nutrient concentrate can replace dietary fishmeal when included at 5-10% without compromising rainbow trout growth and health. Successful incorporation of alfalfa nutrient concentrate in fish feeds can thus improve trout industry sustainability by decreasing marine resource use.

Technical Abstract: The study addresses the escalating demand for feed in the aquaculture industry by exploring the viability of alfalfa nutrient concentrate (ANC) as a feed ingredient for rainbow trout. Five test diets contained varying ANC levels (0%, 5%, 10%, 15%, and 20%) to replace fishmeal (32% in the control diet) and were processed using cooking extrusion method. Analysis of feed pellets showed that pellet density increased proportionally with ANC levels, leading to sinking pellets at 20% ANC, accompanied by improved water stability and durability but reduced oil leakage. Two feeding trials were conducted to test the diets in flow-through water systems, with three replications per diet. The first feeding trial lasted for 8 weeks and focused on feeding, fecal physical quality, and the apparent digestibility coefficient (ADC) of dietary nutrients. ANC inclusion did not significantly impact the palatability and satiation feed intake of rainbow trout. However, the ADC of dry matter and phosphorus significantly decreased in fish fed the 20% ANC diet. The second 9-week feeding trial evaluated the effect of test diets on the growth performance, nutrition quality, and metabolism of rainbow trout. While all fish exhibited substantial growth (specific growth rate: 2.8-3.2% body weight/day, feed conversion ratio: 0.8-1.0), those fed diets with 10% to 20% ANC displayed lower growth rates and higher feed conversion ratios compared to those fed with none or 5% ANC. Whole body composition and plasma biochemical parameters were not statistically different across dietary treatments, except for decreased plasma phosphorus levels in ANC-based diets. Liver metabolomic analysis revealed significant alterations in the metabolism of various compounds (alanine, leucine, valine, threonine, succinate, malate, glycerol 3-P, betaine) and energy metabolism pathways in fish fed the 20% ANC diet. This study offers the first comprehensive assessment of ANC's potential, involving feed management, feeding evaluation, and the biological response of fish. ANC demonstrates a positive influence on feed pellet physical quality without adversely affecting feeding behavior. Nevertheless, optimizing phosphorous digestibility and achieving balanced amino acid profiles as well as their utilization is imperative to maximize ANC utilization in comparison to fishmeal in aquatic feed.