Abstract
Whole egg powder represents a nutrient-dense and functionally versatile ingredient with potential relevance for the development of more sustainable aquafeed formulations. As aquaculture continues to expand, the sector faces increasing pressure to reduce its dependence on conventional marine and plant-based ingredient sources, particularly fishmeal and soy-derived ingredients, which can be associated with resource constraints, price volatility, land-use concerns, and environmental impacts. In this context, whole egg powder offers an alternative source of highly available protein, lipids, essential amino acids, phospholipids, cholesterol, vitamins, and bioactive compounds. ACTIPRO 44EP, a spray-dried whole egg powder, aims to support circular feed strategies by valorising high-quality animal-derived nutrients and reducing reliance on traditional raw materials. This study therefore evaluated the apparent digestibility and nutritional value of ACTIPRO 44EP in diets for juvenile Atlantic salmon (Salmo salar), with the objective of assessing its suitability as a high-quality alternative protein and fat source for salmonid aquafeeds.
The feeding trial followed a standard 70:30 digestibility model, in which the test diet was formulated with 30% ACTIPRO 44EP and 70% basal control diet. This approach allowed the digestibility of the egg powder ingredient itself to be calculated while maintaining comparability with published digestibility studies for aquafeed raw materials. Experimental diets were manufactured using a controlled extrusion process with a Clextral BC45 twin-screw extruder, producing stable 2–3 mm sinking pellets suitable for juvenile salmon. Juvenile Atlantic salmon (Salmo salar), with an initial mean body weight of 55.36 ± 1.21 g, were maintained in a freshwater recirculating aquaculture system (RAS) under controlled environmental conditions, including a water temperature of 15.20 ± 1.0 °C and continuous monitoring of dissolved oxygen, pH, and water quality. Fish were acclimated to the trial system and experimental diets before faecal collections began. During the digestibility phase, fish were fed to apparent satiation across three daily meals, and faeces were collected over a 42-day period using a consistent tank-level protocol designed to minimise nutrient leaching and avoid contamination with uneaten feed. Only fresh, intact, high-quality faecal material was retained for subsequent Apparent Digestibility Coefficient (ADC) analysis.
ACTIPRO 44EP demonstrated very high digestibility values for protein, energy, and individual amino acids in juvenile pre-smolt Atlantic salmon. The calculated ingredient ADC for crude protein was 96%, indicating efficient uptake and utilisation of nitrogen from the egg powder fraction. Essential amino acids also showed high apparent bioavailability, including lysine (94.53%), methionine (99.64%), and threonine (96.88%), which are central to protein deposition, growth, immune competence, and metabolic function in young salmon. In addition to the digestibility outcomes, fish fed the ACTIPRO 44EP diet showed numerically higher final individual body weights after 49 days compared with fish fed the control diet, although the digestibility design means growth performance should be interpreted as supportive rather than definitive. Throughout the trial, twice-daily clinical assessments confirmed that fish remained in good health, with no welfare concerns, abnormal faeces, or negative effects on water quality observed. Overall, the findings indicate that whole egg powder is a highly digestible and nutritionally valuable ingredient for juvenile Atlantic salmon and may represent a promising sustainable raw material for future salmonid feed formulations.