Page 21 - New additives and ingredients in the formulation of aquafeeds

a result of improved villi development, absorptive surface area is enlarged,
leading to better nutrient utilization and enhanced animal health status
and performance.
Soya is a high protein ingredient with favourable price and available in
large quantities on a world-wide basis, thus being an excellent alternative
in plant-based diets. The use of whole soya bean as dietary ingredient is
not recommended due to its high content of anti-nutrient factors (lecithin,
saponins, allergenic proteins, etc.), thus extracted soya is the most
commonly used soya product. The alcohol-soluble fraction of extracted
soya however, still contains active anti-nutrients being ascribed as the
cause of inflammation in distal intestine (enteritis) (Bureau et al., 1998;
Francis et al., 2001; Knudsen et al., 2008). Several investigations have
reported soya-induced enteritis in salmonids (Baeverfjord and Krogdahl,
1996; Krogdahl et al., 2003; Knudsen et al., 2008) and common carp (Urán
et al., 2008). This pathological alteration is microscopically characterized
by hypertrophic mucosa, infiltration of inflammatory cells, hyperaemia,
and shortening of the enterocyte microvilli leading to decreased absorptive
capacity and consequently reduced nutrient utilization and performance
(van de Ingh et al., 1991; Baeverfjord and Krogdahl, 1996; Urán et al., 2008).
Inflammation can either be the cause or the consequence of increased
permeability of intestinal epithelium which is in turn structurally limited
by the tight junctions (Hamer et al., 2008; Knudsen et al., 2008). These
tight junctions are composed of a protein network of sealing strands,
and as demonstrated by Knudsen et al., (2008) increased tight junction
permeability was observed after feeding soya products to fish. As a result
of the increased permeability of intestinal epithelium, susceptibility to
bacterial disease augments (Cheeke, 1999). All these observations have led
specialists to include not more than 5-15% of soya (weight basis) in salmon
diets in order to prevent enteritis, thus limiting higher dietary incorporation
levels of this available source of protein. In this situation, sodium butyrate
arises as a tool to prevent the development of soya-induced enteritis and
allows a more convenient formulation of commercial feeds. As described
in mammals, butyrate provides anti-inflammatory properties in the distal
intestine by modifying transcription factors (NF-kB), which in turn controls
the expression of inflammatory response genes (Hamer et al., 2008;
Le Gall et al., 2009). Additionally butyrate at low concentrations (up to
2mM) increases expression of tight junction proteins (Ohata et al., 2005).
It is documented that the pathophysiological effects of some parasites
as Enteromyxum are partly due to the disruption of tight junctions (Woo
and Buchman, 2011), thus the reduced epithelial permeability associated
to butyrate administration places Gustor Aqua as a new alternative to
maintain intestinal barrier integrity and prevent other further pathological
processes.
Other mechanisms associated to enhanced intestinal defense barrier
have been attributed to butyrate. A first one is production of mucins,
which are glycosilated proteins forming a defense barrier that prevents
invasion of bacteria and protects against damage from bacterial toxins and
Natural growth promoters in aquaculture practices 19