Download Acidify to amplify growth performance

Acidify to amplify growth performance?
Synergy is the key to magnify health
and performance
Ilias Giannenas, DVM, PhD, DipECPVS, Candidate DipECVCN
Laboratory of Nutrition, Faculty of Veterinary Medicine, School of Health Sciences, Aristotle
University of Thessaloniki, 54124 Thessaloniki, Greece.
E-mail: [email protected]
tel:+302310999937; fax:+302310999984
Summary
The recent complete ban on the use of the
antibiotic growth promoting substances by
the EU and partly in several other countries
worldwide urged nutritionists and animal
scientists to seek for alternatives. The use of
organic acids in poultry and pig nutrition appears
to be an interesting solution that can enhance
the effect of other feed additives, as well.
In combination with other substances such as
essential oil compounds from aromatic plants
with established antimicrobial and antioxidant
properties, and the use of exogenous enzymes
organic acids can offer a potential synergistic
activity towards improvement of several health
parameters and growth performance. Organic
acids are administered mainly through the
feed but they may be administered through the
drinking water as well. Successful utilization in
poultry and pig nutrition requires knowledge
of their mode of action. It is generally accepted
that organic acids and their salts lower feed and
gastric pH increasing the activity of proteolytic
enzymes and, thus, improving protein digestion.
Besides, they reduce the buffering capacity of the
feeds, resulting in reduced intestinal colonization
with pathogens. They also improve the apparent
digestibility of proteins and amino acids,
increase the absorption of minerals and affect the
composition of intestinal microflora and mucosal
morphology. Although, the effects of organic
acids, essential oil compounds and enzymes
when used as the only dietary supplements on
performance of poultry and pigs vary considerably,
their combinations demonstrate an increased
consistency and, thus, further research is needed
for a better understanding of the mode of action of
different substances applied in combination.
Over the last two decades there have been increasing concerns over
the use of antimicrobial pharmaceuticals used routinely in farm animal
systems. These concerns arise from: (i) an increasing development
of bacteria, protozoa and macro-parasite resistance to these
pharmaceuticals: the rate of development of resistance to drugs is
much faster than the rate of new antimicrobial and antiparasitic drugs
reaching the market place; (ii) drug residues potentially present in the
food chain and increased consumer interest in the production of food
from animals; and (iii) the consequences of these pharmaceuticals and
their metabolites, when excreted in the environment, on wildlife fauna,
such as invertebrates. For these reasons, in EU countries and other
countries, antibiotics have been totally or partially banned from the
commercial use for farm animals since 1999 and alternatives to control
both microbial and parasitic challenges are been sought. A number
of alternatives growth promoters along with management tools have
been applied to retain a tremendous growth rate with high feed
efficiency mainly in poultry and pig industry. Organic acids and plant
extracts are two important alternatives of great interest to the poultry
and pig industry.
There is a body of literature that organic acids improved growth
performance of poultry, albeit much smaller than in pigs (Dibner and
Buttin, 2002). Amaechi and Anueyiagu ( 2012) demonstrated that
benzoic acid at a 1.2% inclusion level in broiler feed improved weight
gain, suppressed some microbes, and improved growth performance
and gut health of broilers. In agreement, Jozefiak et al. (2010) found
that benzoic acid in low levels (<0.1%) improved chicken performance
while a reduction of the growth rate of broilers was noticed when
fed at higher than 0.1% inclusion levels. These findings can be
explained by the metabolic pathway - conjugation of benzoic acid
with ornithine. These authors further reported that the domestic fowl
excreted benzoic acid and other aromatic acids such as pyromucic,
phenylacetic, p-nitrophenylacetic, and picolinic acids, as well as
nicotinic acid conjugated with ornithine. Feeding high levels of benzoic
acid could result in an arginine deficiency because dietary arginine is
the source of ornithine in the fowl.
Rather than dietary acidifiers, organic acids are better known as
effective preservatives. Their primary antimicrobial action (strainselective growth inhibition or delay) is through pH depression of
the diet. However, more importantly the ability of organic acids
to change from undissociated to dissociated form, depending on
the environmental pH, makes them effective antimicrobial agents.
When acid is in the undissociated form it can freely diffuse through
the semipermeable membrane of micro-organisms into their cell
cytoplasm. Once inside the cell, where the pH is maintained near 7,
the acid will dissociate and suppress cell enzymes (decarboxylases
and catalases) and nutrient transport systems (Lueck, 1980). The
efficacy of an acid in inhibiting microbes is dependent on its pKa
value which is the pH at which 50% of the acid is dissociated. Organic
acids with higher pKa values are more effective preservatives and
their antimicrobial efficacy is generally improved with increasing chain
length and degree of unsaturation (Table 1).
In addition to organic acids, plant extracts offer a unique opportunity
in this regard (Giannenas et al., 2013), as many plants produce
secondary metabolites, such as polyphenols, saponins and tannins,
which have antimicrobial properties. Essential oils (EO), plant extracts,
and certain herbs might be interesting alternative feed supplements
to antibiotic growth promoters (Franz et al., 2010). In recent years,
many herbal plants such as rosemary, sage, thyme, oregano, and tea
or their extracts have attracted wide research interest due to their
antioxidative, antibacterial, and antifungal properties (Giannenas et
al. 2003; 2005; 2013). In a meta-analysis it was demonstrated that
the eubiotic feed additive containing benzoic acid and essential oil
compounds, did improve performance of broiler chicks under semicommercial conditions (Weber et al., 2012).
Poultry and pigs naturally produce enzymes to aid the digestion of
feed nutrients. The benefits of using feed enzymes in diets include
not only enhanced bird performance and feed conversion but also
fewer environmental problems due to reduced output of excreta.
Proteases are added to feed with the purpose of increasing dietary
protein hydrolysis, thus enabling improved nitrogen utilization. When
animals utilize nitrogen better, it is possible to decrease the protein
content in diet and, in turn, also reduce the content of nitrogen in
manure (Oxenboll et al., 2011). Benzoic acid can also reduce urinary
pH (Buhler, 2009). Benzoic acid, after absorption, is transported to
liver where it conjugates with glycine to hippuric acid; in this form
is then excreted to 90% via the urine. This reduction to urinary pH
can markedly reduce ammonia emission (Hansen et al., 2007). Our
in vitro experiments (Giannenas et al., 2014) using protease in low
pH conditions illustrated that the novel serine protease improved
the solubilisation (extraction) and digestion of crude proteins of
experimental feeds. This observation is in good agreement with the
findings of Fru-Nji et al. (2011) showing that protease enhances protein
and amino acid digestibility.
The effect of organic acids on digestibility of nutrients and energy
seems to depend on the type and level of acid applied. In several
experiments, citric-acid exerted no significant influence on digestibility
of crude protein or N retention (Pallauf et al. 1988), although improved
digestibilities of organic matter and gross energy have been observed
(Pallauf et al. 1988). Citric acid is metabolized through the citric-acid
cycle, and may act as an energy source. A positive effect of fumaric
acid on digestibility of organic matter, crude fat and crude protein,
and on N retention have been reported by Kirchgessner & Roth (1980).
On the other hand, several researchers have failed to observe an effect
of these organic acids on the digestibility of crude protein and energy
or N retention (Falkowski & Aherne, 1984), however, benzoic acid
improved crude protein and energy digestibility in pigs (Buhler, 2009).
An explanation could also be that the acidifying potential of benzoic
acid that can activate the enzymes in the GIT (both from endogenous
and exogenous origin).
One of the most influential parameters affecting enzymatic activity
in aqueous solution is pH. But it has no meaning in organic
solvents. Instead, it has been found that enzymes in such media
have a ‘pH memory’: their catalytic activity reflects the pH of the
last aqueous solution to which they were exposed (Klibanov, 2001).
This phenomenon is due to the fact that protein ionogenic groups
retain their last ionization state on both dehydration and subsequent
placement in organic solvents. Consequently, the enzymatic activity
in such media can be much enhanced, sometimes hundreds of times,
if enzymes are lyophilized from aqueous solutions of the pH optimal
for catalysis (Klibanov, 2001). The structure– function relationship
of the molecular memory of enzymes warrants further investigation.
To take full advantage of the opportunities afforded by nonaqueous
enzymology, several mechanistic issues need to be elucidated.
A systematic inquiry should continue into the causes of increased
enzymatic activity in aqueous and acidic solvents compared to
nonaqueous or neutral media.
Low gastric pH is essential for efficient digestion of proteins.
Pepsinogens are rapidly activated at pH 2, but very slowly at pH 4.
Pepsin has two pH optima: 2 and 3,5. Its activity declines rapidly
when pH rises above 3,6, and remains inactive at pH 6 (Kidder &
Manners, 1978). The end products of pepsin digestion and the low pH
of digesta entering the duodenum are involved in the stimulation of
the pancreatic secretion of enzymes and bicarbonate, and they also
play a minor role in regulation of gastric emptying (Maner et al. 1962;
Argenzio, 1984). Acid conditions are also needed to prevent passage
of potentially harmful microbes to the small intestine. A rise in gastric
pH with inefficient digestion may provide an optimal environment for
the colonization of enterotoxigenic haemolytic bacteria on the surface
of villi, resulting in the initiation of scours and/or oedema disease
in young pigs, particularly after weaning (Smith & Jones, 1963). In
our recent trial (Giannenas et al., 2014), the control group was fed
the basal diet, while the other group was given a diet with similar
ingredients and containing benzoic acid and a mixture of essential
oils, protease, and less protein and amino acids. In vitro tests showed
that addition of benzoic acid, the mixture of essential oils, and
protease reduced buffering capacity compared with control feed, and
simulation experiments revealed that the protease increased protein
extraction, hydrolysis, and digestion. The combination of benzoic
acid, essential oils, and protease effectively improved weight gain
and the feed conversion ratio compared with the control, as well as
villus height, lactic acid bacteria counts, and reduced coliform bacteria
counts compared with the control group. As the protease improves the
digestibility of protein, less substrate and/or breakdown products, end
up in the caeca and thus becoming available for pathogens such as
Clostridium perfringens.
The hypothesis that lowering dietary pH with organic acids reduces
gastrointestinal pH has been tested in several studies. Perhaps
owing to methodological imperfections, only a few studies could
document that dietary acidification significantly decreased gastric pH
(Eidelsburger et al. 1992) whereas most studies have failed to show
a significant effect despite quite a large numerical decrease in pH
(Scipioni et al. 1978; Risley et al. 1992). High variations in gastric pH
measurements indicate that it is difficult to obtain a representative
sample, as the proportions of feed and endogenous excretions can
vary from sample to sample. Digesta samples for pH measurements
are generally taken from pigs slaughtered after a certain time
postfeeding. As the diurnal variation in gastrointestinal pH is large,
the sampling time should be standardized relative to feeding time,
and eventually from specific sections of the stomach. Without
cannulation techniques and permanently fixed pH electrodes for
simultaneous measurements in different sections of the stomach
and intestine it may be difficult to assess objectively the full effects
of dietary organic acids on the gastrointestinal pH.
The literature inconsistency might also be due to differences in the
buffering capacity value of the used diets. The buffering capacity value
indicating the amount of acid needed to lower the pH of a feed to a
certain value is important because it affects the course of digestion.
High buffering capacity values in feeds pose higher risks for young
animals, which have limited capacity to secrete gastric acid. When
using feeds with a high buffering capacity, the gastric pH will remain
high, impairing protein digestibility. Undigested protein will reach
the lower digestive tract where excessive protein fermentation may
occur, leading to formation of toxic biogenic amines (Sturkie, 1976).
In addition, poultry feeds with high buffering capacity may result in
proliferation of harmful bacteria in the digestive tract.
Organic acids may improve the absorption of minerals, particularly
Ca and P (Jongbloed & Jongbloed, 1996), although opposite results
have also been reported (Radecki et al. 1988). All organic acids
studied (citric, formic, fumaric, lactic, and propionic) seem to have a
positive effect on Ca and P absorption. Jongbloed (1987) suggested
that lowered intestinal pH increases the solubility of P, which may
improve its absorption. However, the data on ileal pH do not support
this assumption. The effects of organic acids on P digestibility are also
dependent on the amount of phytase, either intrinsic or of microbial
origin, in the diet. Results of Jongbloed & Jongbloed (1996) indicate
that organic acids may have an additional improving effect on the
efficacy of phytase. A synergic effect of lactic acid and microbial
phytase was reported in the study of Jongbloed et al. (1995).
Organic acids also appear to influence the retention of minerals.
Kirchgessner & Roth (1980) reported that 20 g fumaric acid/kg diet in a
weaner diet improved the balance of Ca, P, Mg and Zn by 14, 13, 21 and
43% respectively. The magnitude of effect of organic acids depends on
the type of diet and dietary mineral content. In diets with suboptimal
levels of Zn, 15 g citric-acid/kg diet supplementation has reduced Zn
deficiency symptoms (parakeratosis), but no significant effects on the
apparent absorption and retention of Zn or other minerals (Ca, P, Mg,
Fe, Cu, and Mn) has been found.
Several reports have shown that the use of organic acids may
reduce the coliform burden along the gastrointestinal tract (Cole
et al. 1968; Mathew et al. 1991) and reduce scouring and piglet
mortality. In segments of the small intestine, micro-organism counts
of Lactobacillus/Bifidobacterium, Eubacterium and Bacteroidaceae
were slightly decreased by the addition of 6g formic acid/kg diet
(Gedek et al. 1992). The effect on E. coli counts in ileal digesta were not
consistent, the highest counts being observed for diets supplemented
with 18 g formic acid/kg diet. In the caecum and colon the counts of
Lactobacillus/Bifidobacterium and E. coli were decreased irrespective
of the level of formic acid supplementation. Counts of Lactobacillus/
Bifidobacterium, Eubacterium spp. and also the sum of the main flora
in the duodenum, jejunum and ileum were significantly reduced by the
addition of 18 g fumaric acid/kg diet (Gedek et al. 1992). The influence
of sodium formate was less profound. Fumaric acid also reduced the
Lactobacillus/Bifidobacterium counts in the caecum and colon. E. coli
counts were reduced in the jejunum by fumaric acid treatment, but not
in other segments of the gastrointestinal tract.
Dietary supplementation of benzoic acid, essential oils, and protease
shifted microbiota populations by increasing lactobacillus loads
(Giannenas et al., 2014). Lactic acid-producing bacteria may improve
gastrointestinal function, feed digestibility and animal performance
(Rehman et al., 2006). It is suggested that the establishment of
Lactobacillus spp. prevents the colonization of pathogenic bacteria by
competitive exclusion (van der Wielen et al., 2002). Lactobacilli and
bifidobacteria compete against potential pathogens for nutrients and
binding sites, thereby reducing the intestinal population of pathogens.
Furthermore, lactobacilli and bifidobacteria produce organic acids
and other bactericidal substances (Jin et al., 1998), all of which can
suppress the colonization of the intestine by pathogenic bacteria.
Benzoic acid in combination with essential oil compounds favoured
the growth of lactobacilli and bifidobacteria populations and inhibited
that of coliforms.
Another finding of our study (Giannenas et al., 2014) was a significant
increase in jejunal and ileal villus height. The height of intestinal villi
is connected with the capacity of the bird to absorb nutrients from
feed. Longer villi are typically associated with excellent gut health
and high absorptive efficiency. The structure of the intestinal mucosa
can reveal some information on gut health. Stressors that are present
in the digesta can lead relatively quickly to changes in the intestinal
mucosa, due to the close proximity of the mucosal surface and the
intestinal content. At weaning the small intestine of the piglet generally
undergoes a reduction in villous height and an increase in crypt depth,
changes which are associated with decreased absorption capacity
(Pluske et al. 1996). Similar changes are observed in the epithelium of
the small intestine with a reduction in voluntary food intake (Pluske
et al. 1996) and postweaning diarrhoea (Nabuurs, 1995). Changes in
gut morphology are important as they can reduce growth and prolong
the time pigs take to reach slaughter weight. According to Pluske et
al. (1996), weight gain of weaned piglets is positively correlated with
villous height.
In conclusion, feed additives such as benzoic acid, EOs and enzymes
in combination can improve the growth performance of chickens or
pigs. The combination of benzoic acid with essential oil compounds
together with a pure protease exerted a positive effect on the
performance of broiler chickens and improved gut integrity and some
intestinal microbiota. In vitro experiments revealed that the addition of
protease increased feed protein solubilisation and addition of benzoic
acid reduced the buffering capacity of the feed, together offering
significant support for birds in digesting ingested feed.
References
The references can be provided by the author upon request.
Table 1. Formulas, physical and chemical characteristics of
organic acids used as dietary acidifiers (modified after Partanen
and Mroz, 1999)
Acid
Formula
MM
(g/mol)
Density
(g/ml)
Form
pKa
Solubility in
water
Formic
HCOOH
46.03
1.220
liquid
3.75
++
Acetic
CH3COOH
60.05
1.049
liquid
4.76
++
CH3CH2COOH
74.08
0.993
liquid
4.88
++
Butyric
CH3CH2CH2COOH
88.12
0.958
liquid
4.82
++
Lactic
CH3CH(OH)COOH
90.08
1.206
liquid
3.83
+++
Sorbic
CH3CH:CHCH:CHCOOH
112.14
1.204
solid
4.76
+
COOHCH:CHCOOH
116.07
1.635
solid
3.02-4.38
+
COOHCH2CH(OH)COOH
134.09
liquid
3.4-5.1
++
COOHCH(OH)CH(OH)COOH
150.09
1.760
liquid
2.93-4.23
+++
COOHCH2C(OH)(COOH)CH2COOH
192.14
1.665
solid
3.13-6.40
+++
C6H5COOH
122.12
1.266
crystalline solid
4.20
+
Propionic
Fumaric
Malic
Tartaric
Citric
Benzoic