[ DietDesign By Dr. Elisabeth Holl ]
Organic acids for y
improve digestion
The nutritive effects of organic acids, coupled with their feed hygiene
benefits, make these additives a good choice for incorporation into
diets for young animals.
Diseases of the digestive tract, high mortality rates and an
unsatisfactory growth performance in the rearing period are
some of the main causes for losses in animal production. Digestive disorders in piglets are often caused by the difficulty to adapt
to the transition from milk feeding to solid feed. Stress and a low tolerance against pathogens from the feed may lead to bacterial infections
of the gut and consequently to an increased incidence of diarrhea
and a low utilisation of feed nutrients.
Supporting digestion
It is necessary, then, to support the digestion of piglets through
optimal feed hygiene and the application of suitable additives. The use
of organic acids and their salts is widely accepted in animal nutrition,
although acids differ in their range of effectiveness. On the one hand,
they are preservatives and their efficacy in feed and food hygiene has
been studied extensively. Apart from an improved feed stability due
to their mold-inhibiting and antibacterial properties, acids may also be
used as a mineral and energy source in the animal.
It is also known that different organic acids possess performance
enhancing properties. Using organic acids in the feed utilizes their
antimicrobial properties in the hindgut. This effect is dependent on a
number of factors:
1) the actual concentration in the feed;
2) adsorption and metabolization in stomach and small intestine;
3) activity of the acid at pH 6; and
4) specific activity of the acid.
Most organic acids are effective in a strongly or moderately acidic
environment. Because acids differ in their optimal pH, a blend increases
the general efficacy against microorganisms.
Buffering capacity
Organic acids are also used to reduce the buffering capacity in the
feed. The chemical term buffering capacity (B-value) is used to describe
the change in the pH value of a defined volume or mass after the addition of a strong acid. Usually, in the animal feed sector, hydrochloric
acid is used for this purpose for physiological reasons.
A more practical definition is that the B-value is the amount of 0, 1 N
HCl solution which needs to be added to a 10 percent slurry of the feed
or a feed ingredient in 100 ml of water in order to obtain a pH-value of 5
( 4 or 3). This definition is the reason why we find in practical application
different values for the same expression. In Europe, the most common
B-value is the method developed by Prohaska and Baron (1980). With
the B-value, there exists a neutral measure for the buffering capacity
Figure 1. Contribution of select acids to
reduction of buffering capacity at pH 4
Acid
MM
pKa
Contribution
Formic acid
46
3,75
++++
Acetic acid
60
4,76
+
Propionic acid
74
4,88
+/0
Butyric acid
88
4,82
+/0
Lactic acid
90
3,83
++
Fumaric acid
116
3,02 ( 4,38)
+++
Phosphoric acid
98
2, 10 ( 7& 12)
+++++
of a ration or a single component, which can be determined in the
routine laboratory of the mixed feed manufacturer.
The buffering capacity can provide an indication of the digestibility
of an individual feed or a ration in piglet rearing. The higher the value,
the more critically the component should be evaluated. Lime and
protein sources are especially highly buffering components in the diet.
In the formulation of piglet diets, care should be taken to optimize for
buffering capacity by reducing protein content and using an optimal
amino acid profile. The importance of the buffering capacity can be
shown in figure 1.
In piglet feeds, a buffering capacity of <700 meq/kg is considered
optimal. Higher values are correlated with an increased incidence of
diarrhoea.
In practice, the buffering capacity can be lowered very effectively
with inorganic acids like phosphoric acid. The zootechnical effects,
however, are not equivalent. A low buffering capacity in the feed has a
positive effect on gut health and the development of a healthy intestinal
mucosa. A healthy mucosa is prerequisite for optimal adsorption of
nutrients. This means that one of the parameters that can be positively
influenced by the use of feed acids is digestibility.
