Alfalfa nutrient concentrate provides benefits to diets for rainbow trout

Authors: DENG, DONG - University Of Wisconsin; Samac, Deborah - Debby

Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: 4/1/2024
Publication Date: 5/15/2024
Citation: Deng, D.F., Samac, D.A. 2024. Alfalfa nutrient concentrate provides benefits to diets for rainbow trout. Forage Focus (May 2024):8-9.

Interpretive Summary:

Technical Abstract: A major challenge facing the world in the 21st century is feeding the increasing human population. Not only is the world's population continuing to grow, but the wealth of the population is increasing, and with it the demand for more animal protein in human diets. Aquaculture, the raising of farmed fish and shellfish, is the fastest growing food sector around the world and the most efficient means of providing animal protein to human populations. Traditionally, aquaculture feeds contained high levels of fishmeal derived from wild fish. However, global fishmeal production is declining, and alternative plant-based protein and oil replacements are needed. Alfalfa herbage can be refined into a high protein concentrate (alfalfa nutrient concentrate; ANC) that has an excellent nutritional profile as an alternative to fishmeal. Tests were done to characterize the physical properties of feed pellets with ANC. The bulk density of pellets exhibited a significant increase with addition of ANC in the test diets. The durability index and water stability of pellets showed a significant increase in the diets with 10 to 20% ANC compared to the 0 and 5% ANC diets. While pellets with 0 to 10% ANC maintained floating or neutral buoyancy, approximately 50% or 90% of pellets sank within 20 minutes for the diets with 15 or 20% ANC, respectively. Additionally, the diet with 20% ANC resulted in a significant reduction in oil leaking capacity compared to the control diet without ANC. Thus, the diets based on ANC contribute to increased pellet durability which would have positive implications for feed management. Feeding trials were done with the five test diets and rainbow trout fingerlings to test palatability, satiation feeding, fecal particle distribution, and digestibility. There were no differences for palatability among all dietary treatments. However, the duration of active feeding varied among the different diets. Fish fed the diet with 10% ANC exhibited the longest active feeding duration, while those fed the diet with 20% ANC showed the shortest duration. Fish fed the remaining three diets displayed similar active feeding durations. The apparent digestibility coefficient (ADC) of dietary protein, magnesium, and manganese showed no significant differences among the different diets, but the ADC of dry matter and phosphorus decreased with increasing levels of ANC. The reduced dry matter ADC likely resulted in the lower feed conversion ratio observed for the diets with higher ANC inclusion. However, the test diets did not have any significant impacts on the morphology of the fish or the whole fish, liver, or muscle composition. Future studies are needed to investigate the potential of ANC in a practical feed formulation with a low level of fishmeal and to compare its potential with other plant protein concentrates such as soy protein concentrate and corn protein concentrate.