Improving feed digestibility of low fishmeal diets
T by Phileo Lesaffre
he continually increasing demand for fish farming is driving a shortage in fishmeal supply to the aquaculture industry. As a consequence, fishmeal prices are rapidly increasing and challenging the aquafeed industry to seek economically viable and environmentally sustainable alternatives to fishmeal and fish oil. This quest for alternative ingredients, particularly protein sources, is of utmost importance, especially for supporting the shrimp aquaculture industry. Shrimp is already a heavily traded commodity and its production through intensive aquaculture is expected to continue to notably expand in the coming years.
Pitfalls of plant-based ingredients on feed digestibility
Plant-based ingredients are good candidates to partially replace fishmeal in aquafeeds because they are largely available, fairly economical, and provide a good and reliable source of protein. However, the inclusion of crop-based feedstuffs in shrimp feed is followed by numerous challenges such as reduced feed acceptability and digestibility. Vegetable protein sources, like soy, sunflower, rapeseed, among others, show high content in fibres and include anti-nutritional factors (ANFs). ANFs are biological compounds that reduce nutrient utilisation and feed intake, and comprise molecules including proteinase inhibitors, saponins, and antivitamins alkaloids. These compounds can be deleterious for shrimp growth as they inactivate digestive enzymes and decrease feed digestibility (Bora, 2014). Indeed, both high fibre content and ANFs negatively affect feed intake, FCR and, ultimately decrease shrimp growth performance.
A highly digestible feed additive to supplement low fishmeal diets
In order to address the limitations of replacing fishmeal with plant-based ingredients in shrimp feeds, Phileo Lesaffre developed the feed additive Prosaf® – a premium yeast fraction obtained from the primary culture of a proprietary Saccharomyces cerevisiae baker’s yeast strain. The feed additive Prosaf is produced using a standardised process: after fermentation, yeasts are autolysed through thermal treatment, which is followed by a centrifugation step that separates the cell extract from the cell wall. The latter is discarded, and the inner cell wall fraction is isolated to be subsequently used as a premium and high-quality soluble product. Prosaf feed additive has a high protein content (63%), most of which is comprised of free amino acids and small sized
Figure 1: Amino acid profile expressed in relative proportion compared to fishmeal and soybean meal amino acid composition (Source: Phileo Lesaffre internal data and INRA AFZ tables Soybean meal 44)
Figure 2: Apparent digestibility coefficient of protein, energy, lipid and essential amino acids of four different feeds with a 20 percent inclusion level of Prosaf®, fishmeal, soybean meal, or rapeseed meal (fishmeal LT70, Norvik 70, Sopropêche,l, France; Dehulled solvent extracted soybean meal, Cargill, Spain; Defatted rapeseed meal, Premix, Portugal). Digestibility was measured in whiteleg shrimp (14g average body weight) using yttrium oxide as an inert marker
and highly bioavailable peptides that are easily and rapidly absorbed by shrimp after ingestion. Indeed, 95 percent of this product is composed of molecules smaller than 3.6 kDalton, and 45 percent are even smaller than 1.9 kDalton, as shown by liquid chromatography analysis (HPLC). Prosaf® is also rich in nucleotides (7.7%) derived from yeast cell content, and rich in lysine, threonine, and other essential amino acids that are limited in plant-based feeds (See Figure 1). In order to assure the bioassimilation of nutrients, the digestibility of Prosaf® and essential amino acids was assessed through a digestibility trial conducted by Sparos Lda, Portugal. The in vivo digestibility experiments were performed using
28 | September 2019 - International Aquafeed