Nutrient sparing: a sustainable tool for long-term profitability

Photo: Kakokor

Over the last decade, the aquaculture industry experienced consistent growth mainly in developing countries. Global aquaculture production will clearly continue to grow mainly as a result of improvements in production technology and increased demand for fish and shrimp products. However, aquaculture faces several important challenges in terms of efficient use of the raw materials that need to be addressed.

Contradictory challenges

Several trends put contradictory pressures on the aquaculture industry. Reliance upon scarce and costly raw materials, such as fishmeal, and the optimal use of alternative ingredients constitute a main challenge in aquaculture. Consumer awareness about environmental sustainability encourages producers to improve the production performance through sustainable aquaculture practices.

However, the use of less costly protein sources and low-nutrient dense diets most likely will lead to lower protein digestibility, higher amino acid imbalance, higher carbohydrate and fiber content in feeds. This can lead to inefficient nutrient use, resulting in increased feed usage, greater susceptibility to disease and higher ammonia emissions—raising production costs and increasing the ecological footprint.

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Gut performance holds the key

Optimum animal performance encompasses a number of factors, including genetic characteristics of the species, quality of the diets, environmental conditions and absence of disease outbreaks. Add to this competitive industry pressure and the need for efficient use and/or replacement of increasingly expensive raw materials— and the picture becomes even more complex. A focus on good gut performance and gut health can help to successfully navigate this large set of considerations and set the foundation for better growth. Phytogenic feed additives, consisting of herbs, spices, essential oils and extracts have gained considerable attention as an answer to these challenges.

The active ingredients , such as phenols and flavonoids, can exert multiple effects in animals, including improvement of feed conversion ratio (FCR), digestibility, growth rate, reduction of nitrogen excretion and improvement of the gut microbiota and health status. Examples of these ingredients with major active compounds are provided in Table 1.

Table 1. Important constituents of selected essential oils.

(adapted from Jänicke et al. 2013 and Tisserand and Young 2014)

How phytogenics work

Phytogenics may stimulate the digestive secretions, increase villi length and density and increase mucous production through an increase in the number of globlet cells. Through different strategies, such as matrix-encapsulation, volatile essential oils can be stabilized and may remain active throughout a greater section of the gastrointestinal tract (GIT), thus ensuring that positive effects are not only restricted to a smaller section of the GIT.

Reduced fishmeal content vs. feed efficiency

Replacement of fishmeal by plant protein, whether for economic or sustainable reasons, can decrease feed efficiency and suppress an animal’s immune system due to less digestible raw materials or side effects in the gastrointestinal tract. Digestarom® (BIOMIN Holding GmbH, Austria), a matrix-encapsulated phytogenic additive, has proven to support animals to overcome these challenges and minimize the negative effects of fishmeal reductions and replacements, respectively.

Results in seabream

A first trial was performed with Gilthead seabream (Sparus aurata) at the University of Algarve, Portugal. In this trial, basal diet had 45 % crude protein and 18% lipid content. The majority of the dietary protein content was derived from plant ingredients; the diet contained only 14% fishmeal (FM). Additionally the treatment group received Digestarom®. The aim of the trial was to evaluate the effect of Digestarom® on feed efficiency, body composition and nutrient retention.

Dietary supplementation of Digestarom® showed a significant improvement of 16 FCR-points and an enhancement of the specific growth rate from 1.76% to 1.82% per day (Figure 1). Inclusion of the phytogenic mixture in the diet significantly enhanced (p<0.05) protein and fat retention (Figure 2). The study also showed significant reductions of total nitrogenous losses, which were clearly associated with lower metabolic losses and increased utilization of protein for growth (Figure 3).

Figure 1. Feed conversion ratio (FCR) and specific growth rate (%/day) of sea bream were improved with the supplementation of Digestarom®.
Source: BIOMIN trials, 2012

Figure 2. Nutrient retention of sea bream was enhanced with the supplementation of Digestarom®.
Source: BIOMIN trials, 2012

Figure 3. Nitrogen budget (gain, fecal losses and metabolic losses) in sea bream supplemented with Digestarom®.
Source: BIOMIN trials, 2012

Results in shrimp

A second feeding trial was conducted in collaboration with Ningbo University (China) to evaluate the efficacy of Digestarom® P.E.P. MGE as a tool to reduce the level of fishmeal in shrimp diets. The treatments consisted of 5 isoproteic diets (40% crude protein) with a positive control diet with 25% fishmeal inclusion, and four test diets with two lower levels of fishmeal (22% and 19%) with and without Digestarom® supplementation. Each diet was randomly assigned to 5 replicates of 30 juvenile white shrimp (approximately 0.33±0.00g) and fed over 8 weeks.

The results indicated that the reduction in fishmeal reduced shrimp performance with the control diet (25% FM) having the best performance. Weight gain, feed conversion ratio (Figure 4), specific growth rate (Figure 5) and protein efficiency were improved for shrimp fed the phytogenic additive supplemented diets compared to the lower fishmeal, non-supplemented diets.

Figure 4. Feed conversion ratio of shrimp fed diets with different levels of fishmeal, with and without Digestarom® supplementation.
Source: BIOMIN trials, 2012

Figure 5. Specific growth rate (SGR, %/day) of shrimp fed diets with different levels of fishmeal, with and without Digestarom® supplementation.
Source: BIOMIN trials, 2012

Analysis of mid-gut ultrastructure by transmission electron microscope indicated that shrimp fed the supplemented diets had an improved mid-gut microvilli structure compared to those fed the lower fishmeal diets only (data not shown). The performance improvement of the group given lower fishmeal diets supplemented with Digestarom® is an important result as part of a strategy to reduce costs.


Beyond the clear positive effects on improving feed efficiency, nutrient sparing can be a powerful solution to limit the nitrogen discharge to the environment. Phytogenic feed additives can decrease ammonia emissions through improved protein usage, reducing the loss of nitrogen into the nature.

The presented result shows that the phytogenic feed additive Digestarom® can be used as a nutrient-sparing tool for more efficient and cost-effective diets formulation.