Effects of Supplementation of Acidifier on Birds Performance
A modern challenges in the poultry production is to exploit the use of specific dietary supplements to boost the intrinsic potential of poultry bird to perform better. Antibiotic growth promoters have undoubtedly improved animal performance and health status. It is apparent that antibiotics function by modifying the intestinal microflora. The microbes can develop resistance to these antibiotics and when transferred to human beings, may pose a problem because of the resistance to these antibiotics. This has attracted global attention. Many antibiotics in livestock and poultry production as growth promoters are banned in several countries. Following the ban on the use of antibiotics as growth promoters in animal nutrition by the European Union (EU) in 2006, the nutritionist and researchers attempted other alternatives claiming to enhance the performance of broiler. One of such alternatives was the use of organic acids as feed additive in the animal production. Organic acids and their salts are generally regarded as safe (GRAS) and have been approved by most member states of EU to be used as the feed additives in animal production.
Role of gut microflora:
The gastrointestinal microflora of chicken plays a significant role in nutrition and growth. The competition offered by gut microflora for nutrients in poultry is often managed by in part through the use of low levels of antibiotics. This option is rapidly disappearing. As a result, there is a need to understand the role played by microflora in order to manage its effect on nutrition growth, health and disease by suitable replacements for antibiotics. In chicken, the gut microflora plays a minor role in digestion of feed ingredients. However, the microbes play an important role in absorption of nutrients.
Factors affecting intestinal micro-environment:
- Substrate availability
- Redox potential (used to describe a system’s overall reducing or oxidizing capacity)
- Other bacteria
GIT microbes can be beneficial or harmful. The beneficial bacteria can inhibit the growth of pathogenic bacteria and prevent some specific intestinal diseases such as Clostridium perfringens, E.coli, Salmonella spp. etc. Any disruption in this balance may cause the proliferation of pathogenic or performance hindering microflora. The different microflora in the GIT of chicken is given in Figure 1. The multiplication of harmful bacteria may start from the crop itself. Food stays in the crop for a longer time and the presence of moisture, temperature and time to multiply (depends on food retention time in crop), favors the multiplication of microflora. If acid-producing microbes reduce pH, multiplication of harmful bacteria is reduced.
Classification of Acidifiers:
On the basis of site of action:
- Feed acidifiers
- Gut acidifiers
On the basis of nature:
- Free form
- Salt form
2. Inorganic (Phosphoric acid)
Feed acidification strategies:
Organic acids used in feed:
1. Free acids
2. Salt form
- Free form/unprotected
Feed Acidifiers are acids included in feeds in order to lower the pH of the feed, gut, and microbial cytoplasm thereby inhibiting the growth of pathogenic intestinal microflora. This inhibition reduces the microflora competing for the host nutrients and results in better growth and performance of the chicken. Some of them they also act as mold inhibitors. They are added upto 0.25% of the diet. Most acids are efficacious and their effect remains as long as the acid is not volatilized. The antimicrobial Feed Acidifiers are acids included in feeds in order to lower the pH of the feed, gut, and microbial cytoplasm thereby inhibiting the growth of pathogenic intestinal microflora. This inhibition reduces the microflora competing for the host nutrients and results in better growth and performance of the chicken. Some of them they also act as mold inhibitors. They are added upto 0.25% of the diet. Most acids are efficacious and their effect remains as long as the acid is not volatilized. The antimicrobial effect of organic acid ions in controlling bacterial populations in the upper intestinal tract leads to beneficial effects.
Modes of Action:
The antibacterial action of organic acids depends on whether the bacteria are pH sensitive or not. Only certain types of bacteria are sensitive to pH (ex.E. coli, Salmonella spp, L. monocytogenes, C. perfringens) while other types of bacteria are not sensitive (Bifidobacterium spp., Lactobacillus spp).
A. For pH sensitive bacteria:
The mode of action in pH sensitive bacteria is shown in Figure 2. Organic acids in undissociated (non-ionized, more lipophilic) state penetrate the semi permeable membrane of bacteria cell wall and enter cytoplasm. At the internal pH of bacteria (~7.0), the undissociated organic acids dissociate, releasing H+ and anions (A-). The internal pH of bacteria decreases. The pH sensitive bacteria are unable to tolerate a large spread between the internal and the external pH. A specific H+ -ATPase pump acts to bring the pH inside the bacteria to a normal level. This phenomenon consumes energy and eventually can stop the growth of the bacteria or even kill it. The lowering of pH also suppresses the enzymes (e.g. decarboxylases and catalyses), inhibit glycolysis, prevent active transport and interfere with signal transduction. The anionic (A-) part of the acid trapped inside the bacteria (it can diffuse freely through the cell wall only in its non-dissociated form), becomes toxic involving anionic imbalance leading to internal osmotic problems for the bacteria.
Thus, the antibacterial effect of organic acids is by:
- Modification of bacteria internal pH
- Inhibition of bacteria fundamental metabolic functions
- Accumulation of toxic anions in bacteria
- Disruption of bacteria cellular membrane
B. For non-pH sensitive bacteria:
The non-pH sensitive bacteria tolerate a larger differential between internal and external pH. At a low internal pH, organic acids re-appear in a non dissociated form and exeunt the bacteria. Equilibrium is created and the bacteria do not suffer.
Role of poultry feed acidifiers:
Effects of poultry feed acidifiers on different parametersL:
Effect on gut health:
Effect of feeding different organic acids on gut health of broiler (Ghazalah et al., 2011):
|Treatments||Level (%)||Villus height (µm)|
Sheikh et al. (2011) studied the effect of incorporation of 2 and 3% level of butyric, fumaric and lactic acids on length of villus height and reported that groups of birds received the organic acids showed increased villus height, but 3% butyric acid supplemented group revealed the most significant effect on villus height of duodenum (1410.38 ± 46.41µm), jejunum (1256.94 ± 48.08µm) and ileum (898.85 ± 103.8µm) in comparison to respective values for control (1166.88 ± 56.32µm, 984.0.5 ± 25.77µm and 676.13 ± 49.03µm). These findings were supported by other research worker as well (Gunal et al., 2006; Paul et al., 2007; Ghazalah et al., 2011; Taklimi and Ghahri, 2012).
Gut sections showing effect of organic acids on villus height:
a= control group (duodenum); b= 3% butyric acid; c= control group (jejunum); d= 3% fumaric acid; e= control group (Ileum); f= 2% fumaric acid
Effect on nutrients digestibility:
Ghazalah et al. (2011) reported the effect of feeding four different types of organic acid on nutrient digestibility. The effect of dietary formic acid, fumaric acid, acetic acid and citric acid on nutrient digestibility are listed in below mentioned table:
|0.25% Formic acid||92.72a||74.31||26.05||79.95|
|0.5% formic acid||93.16a||77.39||28.27||80.89|
|1.0% formic acid||93.32a||74.92||31.09||79.66|
Effect of feeding formic acid on nutrient digestibility-digestibility of crude protein was increased significantly in all formic acid supplemented group, however there was no significant effect on digestibility of ether extract, crude fibre and nitrogen free extract.
Ghazalah et al. (2011) reported that fumaric acid supplementation led to significant increase in digestibility of crude protein, ether extract and nitrogen free extract, however there was no effect on digestibility of crude fibre.
Effect on blood biochemistry:
Ghazalah et al. (2011) compared the effect of different type and levels of formic acid (0.25, 0.5 and 1.0%), fumaric acid (0.5, 1.0 and 1.5%), acetic acid (0.25, 0.5, and 0.75%) and citric acid (1, 2 and 3%) on blood metabolites and reported that level of calcium, phosphorus, total protein and globulin were increased in all the treatment groups.
Effects of different level of formic acids on blood constituents (Ghazalah et al., 2011):
Effect on carcass characteristics:
Sheikh et al. (2011) studied the effect of incorporation of 2% and 3% level of butyric acid, formic acid and lactic acid on dressing percentage and organ weight of broilers. There was insignificant improvement in dressing percentage between the (T) treatment and (C) control group, however there was no effect on organ weight (heart weight (C) 10.33 ± 0.3g Vs (T) 10.0 ± 1.00g, liver weight (C) 41.66 ± 3.17g Vs (T) 50.0 ± 1.73g). The intestinal weight was increased significantly for the bird fed 3% lactic acid supplemented diet ((C) 43.36 ± 1.16g Vs (T) 53.60 ± 1.00g). Similar findings were also reported by various researchers (Denli et al., 2003; Aghazadeh and Yazdi (2012); Kamal and Ragaa (2014).
Effect of organic acid on dressing percentage and organ weight (Sheikh et al., 2011):
|2% butyric acid||3% butyric acid||2% formic acid||3% formic acid||2% lactic acid||3% lactic acid|
|Dressing percentage |
|Liver weight (g) |
|Heart weight (g) |
|Intestinal weight (g) |
- Organic acid supplementation composed of individual acids and blend of several acids reduces the pH of gastro-intestinal tract, hence decreases the total count of pathogenic bacteria significantly.
- Supplementation of organic acids viz. butyric acid, fumaric acid, lactic acid leads to remarkable increase in morphology of small intestine in terms of villus height, weight and length and improves the availability of nutrients to the host .
- Supplementation of organic acids viz. fumaric acid, formic acid, acetic acid, lactic acid Significantly increases the body weight gain in most of the Studies.
- Organic acid supplementation also leads to improvement in Feed Conversion Ratio.
- Organic acid supplementation decreases the cost of broiler production, hence increases the margin of profit.
- Inorganic acids help to decrease the pH and extending the time of exposure of pathogens to an unfavourable acidic environment. This helps to eliminate a higher number of bacteria, decreasing the transit passage to the intestine.