the use of dietary acidifiers in salmonid nutrition

8/14/2019 The use of dietary acidifiers in salmonid nutrition

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Digital re-print - March | April 2009Feature: Acidifers

Feature title: The use o dietary acidifers in salmonid nutrition

International Aquafeed is published five times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies,

the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis ofinformation published.Copyright 2009 Perendale Publishers L td. All rights reserved. No par t of this publication may be reproduced in any formor by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

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Routine use of antibiotics

as growth promoters is a

matter of debate in the

animal farming industry.

The use of low levels of these antibiotics

in animal feeds possesses the possibilityto transfer bacterial immunity to species

pathogenic in animals and humans (Liem,

2004). The EU banned all antibiotic growth

promoters (AGP) from livestock produc-

tion from January 2006.

Public opinion and regulation authorities

in most of the export countries focusing

now on the misuse of antibiotics in aqua-

culture and public attention have shifted

towards production methods.

Therefore, alternatives to AGP are

worldwide sought in a variety of forms.

Acidifiers consisting of organic acids and

their salts present a promising alternative

and they have received much attention as a

potential replacement in order to improve

the performance and the health of treatedanimals. In animal nutrition, acidifiers exert

their effects on performance via three

different ways (Freitag 2007): a) in the

feed; b) in the gastro-intestinal tract of the

animal; and c) due to effects on the animals

metabolism.

Role of feed

A certain amount of fungi, bacteria or

yeast is unavoidable in feeds. Under favour-

able conditions such microbes multiply

rapidly during storage, especially at higher

moisture levels (>14 percent) in a warm

environment.

Acidifiers function as conserving agents

by reducing the pH of the feed, and thereby

inhibiting microbial growth and thus lower

the uptake of possibly pathogenic organ-

isms and their toxic metabolites by the

farmed animals (Freitag 2007). Malicki et al.

(2004) found that a mixture of formic and

propionic acid (one percent dosage) can

act synergistically against

E. coli in stored fishmeal,

which is an often used

ingredient in aquafeeds.

Role in intestinal

tract

The mode of action

of organic acids in the

intestinal tract involves

two different ways: on

one hand they reduce the

pH-level in the stomach

and particularly in the

small intestine, and on theother hand inhibit growth

of gram-negative bacteria

through the dissociation

of the acids and produc-

tion of anions in the bac-

terial cells.

During periods of high feed intake such

as when the animals are young, or when the

feeds are high in protein, free hydrochloric

acid levels in the stomach are reduced.

This reduction negatively impacts pepsin

activation and pancreatic enzyme secretion

and impairs digestion. Providing acidifiers in

the feed tackles this problem and aid in feed

digestion (Eidelsburger 1997).

Positive effects of organic acids on pro-

tein hydrolysis have been demonstrated

(Mroz et al. 2000). Likewise feed sup-

plementation with organic acids has been

shown to lead to lower duodenal pH,

improved nitrogen retention and overallincreased nutrient digestibility (verland et

al. 2000; Kluge et al. 2004).

Growth rates of many gram-negative

bacteria, like E. coli or Salmonella ssp. are

reduced below pH5.

Low pH also forms a natural barrier

against ascending microbes from the ileum

and large intestine. Moreover, small acids

are lipophilic and can diffuse across the cell

membrane of gram-negative bacteria.

Table 1: Gross energy content of selected organic acids andtheir salts used in aquaculture feeds (modified from Freitag2007)

Organic acid/salt Solubility inwaterGross energy

(kcal/kg)

Formic acid very good 1385

Acetic acid very good 3535

Propionic acid very good 4968

Lactic acid good 3607

Citric acid good 2460

Calcium formate low 931

Sodium formate very good 931Calcium propionate good 3965

Calcium lactate low 2436

Potassium diformate good 2725

10 | InternatIonalAquAFeed | Mch-api 09 - i

Acidifiers

by Christian LckstdtAddcon Nordic AS3908 PorsgrunnNorway

Email: [email protected]

The use of dietary acidifiers

in salmonid nutrition

A REVIEWIn the more alkaline cytoplasm they

dissociate and cause pH reduction. This

reduction alters cell metabolism andenzyme activity thus inhibiting growth ofintraluminal microbes, especially pathogens.

Several investigations demonstrate areduction in bacterial count in the stomach(Kluge et al. 2004) and the duodenum

(Kirchgessner and Roth 1991; Hebeler et

al. 2000; Hellweg et al. 2006), while acid

tolerant beneficial Lactobacillus spp. seemto be unaffected or may even be enhancedin number (Hellweg et al. 2006).

Role in metabolismMost organic acids have a consid-

erable amount of energy (Table 1).

Organic acids are generally absorbedthrough the intestinal epithelia by pas-sive diffusion. Short chain acids can beused in various metabolic pathwaysfor energy generation, for instance forATP generation in the citric cycle. Asthe energy content of organic acids iscompletely used in metabolism it shouldbe considered in the energy calculationof feed rations.

For example, propionic acid containsone to five times more energy than wheat(Diebold and Eidelsburger 2006).

Organic acids in aquacultureAcid preservation of fish and fish

viscera to produce fish silage has beena common practice and its final producthas been widely used in fish feeds withreported beneficial effects (Gildbert

and Raa 1977; sgrd and Austreng1981).

The beneficial effects of acid preservedproducts caught the attention of the scien-tific community to investigate the effects of

these short-chain acids onto the fish feeddirectly.

Several studies have been conductedwith different species including carnivoreslike rainbow trout Oncorhynchus mykiss,Atlantic salmon Salmo salar and artic charrSalvelinus alpinus, herbivorous filter feeders(tilapia), omnivorous fish (carp, catfish) and

shrimp.F o l l o w i n g

experiences inswine and poultryfeeding, a widevariety of organicacids, their salts as well as blendsof those is andwas tested inaquaculture diets(Table 2).

Effect ofacidificationin salmonids

Early studieson organic acids infish diets included

succinic and citricacid in salmonids( F a u c o n n e a u

1988). In this study

the partial substi-tution of protein(12 percent) by a

single amino acidor an organicacid (either suc-cinic or citricacid) was tested

in rainbow trout(Oncorhynchus

mykiss) diets.

Trout, which fed the organic aciddiets, had a lower voluntary feedintake, compared to the basal diet, orto a diet additionally supplementedwith purified protein.

However, there was no large vari-ation between the tested groups inthe efficiency of utilisation of proteinand energy.

Data from the 1990s obtainedmore promising results in the useof dietary acidifiers in a number ofsalmonid species (Table 3).

The effect of supplementation ofcommercial diets with sodium salts oflactic and propionic acid was testedin Arctic charr (Salvelinus alpinus) in

brackishwater at 8C (Ring 1991).

Fish fed the diet with one percentadded sodium lactate increased in weightfrom about 310g to about 630g in 84 days,while fish fed diets without either saltsreached a final weight of only 520g (P


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ing the results, is the difference in the

retention of dietary lactate in the stomach,

which was twice as long in Arctic charr.

According to the authors, it seems likely

that lactate or lactic acid exerts its influence

in the upper part of the digestive system

and therefore any difference found here

may explain the variation in growth rate

between the two fish species.

However, a beneficial result of the acidi -fied diet may be the numerical reduction of

mortality from 19.9 percent in the negative

control to 15.2 percent in the lactate fed

salmons.

The effect of organic acidson digestibility of minerals

Further studies on salmonids included

again the rainbow trout Oncorhynchus

mykiss. The effect of organic acids on digest-

ibility of minerals was tested in several

studies.

It was reported from pigs, that the

inclusion of dietary organic acids enhances

the mineral absorption (Ravindran andKornegay 1993).

Since especially the availability of phos-

phorous from a

fishmeal-based diet

plays a vital role in

salmonid aquacul-

ture (sgrd andShearer 1997), differ-ent acidifiers were

tested on such pos-

sibilities. Vielma and

Lall (1997) reportedthe effect of dietary

formic acid on the

availability of phos-

phorous in such

diets for rainbow

trout.

It was found that

the apparent digest-ibility of phospho-

rous was significantly

increased (P


4/5

The solution behind the solution.

Bhler AG, Feed & Biomass, CH-9240 Uzwil, Switzerland, T +41 71 955 11 11, F +41 71 955 28 96

[email protected], www.buhlergroup.com

Its the mix that makes the dierence. Feed manuacturers desire high

durability, reliability and sanitation. Quality eed with minimum operating costs is

a must. Your needs are Buhlers frst priorit y. That is why we commit our-

selves to delivering seamless solutions meeting your highest requirements. Get

in touch with one o our specialists worldwide and we will deliver a complete

process design package, equipment, automation and customer service. You and

Buhler the perect mix.

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V OLUME 12 IS SUE 2 2009

Ipil ipil leaf meal as supplementsto soybean and fish meal

Functional aquafeeds:Dietary supplementsin breakthrough pledge

Adding value tofeathermeal

The use of dietary acidifiers insalmonid nutrition

ExtrudersBenefitsof using Extrudersto

processaquatic feed

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The solution behind the solution.

BhlerAG,Feed &Biomass,CH -9240 Uzwil,Switzerland,T+41 71 955 11 11,F+41 71 955 28 96

[email protected],w ww.buhlergroup.com

Its the mix that makes the dierence. Feed manuacturers desire high

durability, reliability and sanitation. Quality eed with minimum operating costs is

a must. Your needs are Buhlers frst priority. That is why we commit our-

selves to delivering seamless solutions meeting your highest requirements. Get

in touch with one o our specialists world wide and we will deliver a complete

process design package, equipment, automation and customer service. You and

Buhler the perect mix.

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