Studying the effect of organic acids on broiler chicken nutrition

The modern broiler industry requires high levels of productivity and efficient feed-to-meat conversion, which can be achieved in part through the use of specific feed additives [1].

The use of antibiotics in poultry feed has been common worldwide since the mid-20th century [2]. These antibiotics are added to animal feed at both therapeutic and subtherapeutic levels to promote better growth and feed efficiency [2].

However, there is increasing awareness and recognition of the negative consequences of using antibiotics as growth promoters; these include:

Antibiotic resistance in humans and animals

Residency of drugs in livestock products

Potential toxicity

And environmental contamination

For this reason, several countries have banned the use of antibiotics in farm animal production [2].

This ban has led to the emergence of alternative approaches to maintaining animal health and growth; These include:

Organic acids
Prebiotics
Probiotics
Enzymes
Essential oils
Bacteriophages
Phytogenic additives [3, 4]

Among these alternatives, organic acids and their salts (either individually or in combination) have attracted much attention worldwide as effective alternatives to antibiotic growth promoters. The main reason for this attention is the increasing global demand for antibiotic-free and organic poultry production, as these compounds have been able to improve poultry health and performance [5].

The term “organic acids”, also commonly referred to as “acidifiers”, refers to a broad range of naturally occurring chemical compounds found in plants, animal tissues, and microbes, and play a role in many vital processes in the body [6].

Chemically, organic acids share common characteristics such as:

Solubility in water

Acidic properties

Absence of primary or secondary amino groups (as determined by a negative ninhydrin test) [6].

Organic acids generally contain a carboxylic acid group (R-COOH) and are known as weak acids that act as biochemical intermediates in the metabolism of amino acids, sugars, and fatty acids.

In livestock and poultry feed, these acids are used for the following reasons:

High nutritional value

Antibacterial properties

Role in stimulating energy metabolism [5]

Several types of organic acids are frequently used as feed additives in animal diets (see Table 1).

The mechanism of action of these acids is directly dependent on the pH of the environment and their pKa value [4].

The use of organic acids and their salts as non-antibiotic feed additives in livestock and poultry production is generally recognized as safe and has been approved by the European Union [8].

Use of organic acids in poultry diets and their mechanism of action

Over time, organic acids have been included in animal diets worldwide due to their antibacterial properties. These acids can exert their positive effects by reducing the pH of the digestive tract. Most organic acids with antimicrobial properties have a pKa value between 3 and 5 [7].

Organic acids help improve growth performance by increasing the availability of nutrients in the feed, increasing the solubility of nutrients in the digestive tract, and facilitating the process of digestion and absorption of nutrients [9]. Research has shown that the use of organic acids and their salts increases proteolysis (protein breakdown) in the stomach and improves the digestibility of proteins and amino acids [10].

This review article presents new findings on the antimicrobial effects of organic acids as well as their effects on growth performance, gut health, and carcass and visceral characteristics in broiler chickens.

Mechanism of action of organic acids:

Similar to antibiotics, organic acids have antibacterial properties that play an important role in gut health and development, ultimately increasing animal productivity and health. These acids have bacteriostatic (inhibiting bacterial growth) and bactericidal (killing bacteria) properties.

A study cited in [11] shows that the dissociation properties of organic acids are directly related to their mechanism of action. These acids can cross the bacterial cell wall and disrupt the physiological function of many pathogenic microorganisms [6].

At low pH conditions, organic acids are very effective, especially in the non-ionized state, making them potent antimicrobial agents [7].

In the non-ionized state, organic acids are lipophilic (fat-loving) and can easily cross the cell membrane of bacteria and fungi. Once inside the cell, these acids dissociate, lowering the internal pH of the cell and disrupting the vital processes of the cell [7, 10].

This process results in the production of protons (H⁺) and anions, causing the pH inside the cell to drop below 4.5, which is detrimental to pH-sensitive bacteria such as coliforms, Clostridium, and Listeria, while more resistant bacteria such as Lactobacillus and Bifidobacterium are able to continue their activity [4]. The acidic environment inside the cell disrupts the function of enzymes, transport systems, and energy-producing processes, ultimately leading to the inhibition of bacterial growth (bacteriostasis) [12].

To restore the internal pH of the cell to normal and maintain the function of biological molecules, bacteria are forced to excrete protons through the enzyme H⁺-ATPase [13, 14]. This enzyme requires a large amount of adenosine triphosphate (ATP) for its function. As a result, the cell’s energy stores are gradually depleted and the bacteria die due to the loss of vital energy [14].

Antimicrobial effects of organic acids

Intestinal microflora plays a vital role in the digestion and immune function of poultry, ultimately leading to increased growth performance in them [15]. Common pathogenic bacteria that can compromise the health of the digestive tract of poultry include Salmonella, Escherichia coli (E. coli), Campylobacter, and Clostridium perfringens. The growth and proliferation of these bacteria can be effectively controlled by adding organic acids to the diet or drinking water of birds.

Several studies have shown that organic acids in the diet improve feed intake and growth performance of poultry by inhibiting the growth and proliferation of pathogenic microorganisms while increasing the population of beneficial microbes in the digestive tract [5, 16–18].

In a study conducted by Emami et al. [19], it was found that the microbial flora of the cecum (caecum) of broilers fed diets containing a combination of organic acids (0.05%–0.1% formic acid and propionic acid) was altered.
The result of this alteration was an increase in the population of Lactobacilli and a decrease in the population of E. coli.

Also, the addition of a mixture of encapsulated essential oil with organic acids at a rate of 500 mg/kg of feed to broilers, both in the E. coli-challenged and unchallenged groups, effectively reduced the population of E. coli in the cecum of broilers, without having a significant effect on the population of Lactobacilli [20].

Antimicrobial effects of organic acids

Similarly, dietary supplementation with a coated mixture of plant essential oils and organic acids at doses of 300, 500, and 800 mg/kg in broiler chickens infected with Salmonella enteritidis resulted in a reduction in Salmonella bacterial load in the cecum, liver, and spleen [21].

In recent studies, broiler chickens fed 0.50 and 0.1% formic acid, 0.50 and 0.1% acetic acid, and 0.2 and 0.3% citric acid showed significant reductions in total bacterial counts, including Escherichia coli and Proteus. At the same time, a significant increase in the population of Lactobacilli was observed [22].

According to the report of Obaid et al. [23], giving a mixture of propionic acid and acetic acid in the ratio of 0.06% in the drinking water of broilers reduced the presence of Salmonella and E. coli in the intestine compared to the control group. In the same study, adding a mixture of organic acids in the ratio of 0.03% caused

Bacillus subtilis population was increased in breast meat of broilers, while 0.06% of this compound resulted in a decrease in total bacterial and E. coli counts [23].

Also, Islam et al. [24] reported that Clostridium perfringens, E. coli and Salmonella were reduced in chickens fed a combination of organic acids and essential oils. In an experiment conducted by Bourassa et al. [25], the addition of formic acid and propionic acid to the diet of broilers at a concentration of 1 to 5 kg per ton of feed resulted in a decrease in Salmonella levels in the caeca.

The potential of organic acids to inhibit the growth of harmful bacteria in the digestive tract and breast meat of poultry can be attributed to the reduction in pH, which effectively inhibits the proliferation and spread of pathogenic bacteria. On the other hand, acidophilic bacteria such as Lactobacilli are able to tolerate changes in pH between the internal and external environment of the body [26].

Manawatkar et al. [9] reported that the addition of 1 g/kg of a coated organic acid compound to the feed of broiler chickens resulted in a significant reduction in the population of caecal bacteria. In addition, a significant reduction in the total number of bacteria in the caecum was observed in chickens fed the organic acid-containing diet [27]. This observed reduction in the total number of viable microorganisms is attributed to the antibacterial properties of the coated organic acids. These acids are believed to enter bacterial cells and reduce microbial viability and activity by lowering intracellular pH.

A significant increase in the population of Lactobacilli was also observed in the faecal microbial community of broilers fed a diet containing a combination of medium-chain fatty acids and organic acids [28]. Several studies have shown that organic acids in the diet of broilers can improve the beneficial microbial composition of the gastrointestinal tract, particularly by increasing the population of Lactobacillus spp. [29]. Increasing the population of Lactobacilli has a positive effect on intestinal function, as it reduces the viability of enteric pathogens by producing acidic conditions resulting from the fermentation of Lactobacilli [28]. By reducing the population of pathogenic microorganisms, the metabolic demands of these microbes are also reduced, which increases the animal’s access to energy and nutrients from the diet.

Effects of Organic Acids on Growth Performance

The use of organic acids as growth promoters to improve poultry performance has gained increasing importance (see Table 2). There is increasing scientific evidence that broilers fed diets containing different sources and concentrations of organic acids perform better in terms of growth performance [40]. The growth-promoting effect of organic acids is attributed to their ability to regulate the gastrointestinal microbiota, improve the intestinal microscopic structure, activate the immune system, and stimulate the secretion of various digestive enzymes [17, 41]. According to a study by Fik et al. [30], adding citric acid to the drinking water of broilers at different levels (0.5%, 1.0%, and 1.5%) increased body weight compared to the control group. The 1.5% citric acid concentration had the greatest effect on growth performance. The improvement in body weight gain is most likely due to the positive effect of citric acid on the gut microbiota.

In a study by Islam et al. [24], the addition of a mixture of organic acids at 200 mg/kg (alone or in combination with 150 mg of essential oils) to the diet of chickens increased body weight gain and feed intake without affecting feed conversion ratio (FCR), compared to the control group and the group receiving 50 mg of enramycin. Also, in another study, the addition of a mixture of organic acids and essential oils to the drinking water of chickens resulted in an increase in average body weight and daily weight gain [32]. In another study, the addition of 800 mg/kg of buffered sodium butyrate to the diet significantly increased daily weight gain, daily feed intake, and improved FCR compared to the group receiving antibiotics [31]. Addition of 0.3, 0.6, and 1 g/kg of the protected organic acid mixture to the chicken diet also increased weight gain and improved FCR compared to the control group [9]. The best performance was associated with the 1 g/kg dose, which showed the highest final weight (2806.70 g) and better FCR (1.50). According to the findings of Ma et al. [33], the addition of 3000 and 6000 mg/kg of the mixed organic acids to the chicken diet resulted in a significant increase in daily weight gain, final weight, and FCR, without a significant effect on daily feed intake. According to the report of Noormohammadi et al. [42], acidifiers, including organic acids, have a positive effect on performance by increasing nutrient efficiency and improving digestibility. Rehman et al. [35] also found that adding 10, 20, and 30 g/kg acetic acid to the diet of chicks from 8 to 42 days of age increased weight gain and improved FCR. The observed improvement in feed conversion ratio (FCR) may be due to a reduction in feed intake, which ultimately led to weight gain; this occurs due to increased nutrient efficiency. According to Katoch et al. (36), feeding commercial broilers with 0.5% citric acid in diets with low or relatively low mineral density (calcium and phosphorus) increased daily weight gain (BWG) and reduced mortality compared to the control group.

Also, Salgado-Tránsito et al. (43) reported that broilers fed 6.25, 12.5, 25, or 50 g citric acid/kg

The feed from day 1 to 28 had improved FCR and higher live weight than the control group. The results showed that the chickens that received 50 g citric acid per kg of feed had the highest live weight (1013 g) and better FCR (1.55).

The observed improvement in broiler growth performance due to the addition of organic acids can be attributed to several factors, including:

Increase in energy and protein content of the diet;

Reduction in pathogenic microorganisms;

Immune system enhancement;

Reduction in the release of infectious agents;

Reduction in ammonia and other harmful metabolites;

Organic acids are well known to enhance overall performance by reducing the total microbial load and reducing microbial competition for nutrients in the digestive tract. This reduces the risk of subclinical infections, increases feed digestibility and reduces the energy requirements of tissues associated with the digestive tract.

In addition, organic acids play vital physiological roles in the digestive tract. One of these roles is the conversion of inactive pepsinogen to its active form, pepsin. Organic acids also serve as important energy sources in the digestive tract and are effective in regulating the rate of gastric emptying. In addition, these compounds can increase the production of endogenous enzymes and, by chelating minerals, affect their availability and absorption [13].

Effect of organic acids on intestinal health

Indicators related to intestinal histomorphology, such as villus height, muscle thickness, crypt depth, villus area, epithelial thickness, and villus height to crypt depth ratio, are important markers for assessing small intestinal function. In addition, goblet cells are known to be a reliable marker of intestinal function due to their role in the production of mucus, a substance that coats the surface of the epithelium and acts as a protective barrier against the adhesion of harmful microorganisms [47].

Various investigators have documented the positive effects of adding organic acids to the diet of broilers on intestinal histomorphometry [25, 47]. Adding mixed organic acids at 3000 mg/kg and 6000 mg/kg to the diet of broilers had a positive effect on crypt depth, villus height, and the ratio of villus height to crypt depth in different segments of the small intestine of 21- and 42-day-old broilers [33]. However, an opposite finding has been reported in broilers fed a mixed liquid acid additive and essential oils in their drinking water [32].

According to Khosrowinia et al. [38], adding 30 g/kg and 60 g/kg citric acid to broiler feed had a positive effect on villus length, crypt depth, and villus length to crypt depth ratio in the duodenum, jejunum, and ileum of 42-day-old broilers. Also, Manotkar et al. [9] reported that 42-day-old broilers fed a diet containing 0.6 and 1 g/kg of coated organic acids had higher intestinal villus heights in the duodenum, jejunum, and ileum than the control group. Similarly, a study by Rahman et al. [35] reported that the addition of acetic acid at 10, 20 and 30 g/kg feed to the diet of broiler chickens significantly (p < 0.05) improved duodenal villus height, crypt depth and villus area in 49-day-old broilers. Broilers that had 30 g of acetic acid added to their diet had the highest duodenal villus height (1379.70 μm), deeper crypt depth (229.33 μm) and larger villus area (0.3167 mm2). In addition, the addition of acetic acid also increased jejunal and ileal villus height, jejunal villus area and ileal crypt depth. Broilers fed 30 g acetic acid per kg of feed showed the highest villus height in the jejunum (147.43 μm) and ileum (828.00 μm). However, the addition of acetic acid to the broiler diet had no significant effect on crypt depth or villus surface area in the jejunum or ileum.

The results of Sikander et al. [37] showed that, compared with control chickens, broilers fed sodium butyrate (0.5 and 1 g/kg of feed) for 21 and 35 days showed increased villus surface area, villus height, and villus height to crypt depth ratio in different parts of the small intestine. This could be because butyrate acts as a very abundant energy source for enterocyte cells in the intestine, which probably increases cell mitosis in the crypts.

Similarly, Ogwegbo et al. [48] found that the addition of sodium butyrate at 4 g/kg to broiler diets significantly increased villus length, crypt depth, epithelial thickness, and muscle thickness in the duodenum, jejunum, and ileum of breeder and finisher chickens. Sodium butyrate promoted the proliferation of enterocyte cells in the intestinal mucosa and the elongation of villus, resulting in increased villus height and greater crypt depth [8].

Zhao et al. [34] reported that broilers fed chemically preserved sodium butyrate (1000 mg/kg) had greater villus height to crypt depth ratios in the duodenum, jejunum, and ileum of 21-day-old chickens compared with the control group and the group fed antibiotics in the diet. Furthermore, crypt depth in the duodenum, jejunum, and ileum of 21-day-old broilers was not significantly different between chickens fed a control diet, a chemically preserved sodium butyrate diet, and a diet containing antibiotics.

Sun et al.

[49] concluded that the addition of organic acids to broiler diets at different levels (500, 1000 and 1200 mg/kg) increased duodenal villus height, crypt depth and jejunal villus height compared to the control group. Broilers fed 1000 and 1200 mg/kg of organic acid products had the highest duodenal villus height (4045 and 4085 μm, respectively). Compared with the control diet, the addition of 1000 or 1200 mg/kg of organic acid products to the broiler diet reduced villus height in the ileum. However, the jejunal and ileal crypt depths and the ratio of villus height to crypt depth were not significantly changed.

The observed improvements in villi height, villi surface area, and crypt depth in the small intestine of broilers may be due to the acidic nature of organic acids, which create an unfavorable environment for harmful bacteria and pathogens by lowering the pH of the digestive tract. This promotes the growth of beneficial bacteria, which can improve nutrient absorption and reduce intestinal inflammation. As a result, intestinal villi can grow longer and absorb nutrients from the feed more effectively.

Furthermore, Liao et al. [50] found a strong association between organic acids and gut microbial populations in promoting the development of healthy gut architecture in broilers. Organic acids have also been shown to stimulate the production of digestive enzymes, which improves nutrient absorption and overall gut health.

Effect of organic acids on carcass and internal organ characteristics

According to Malematja et al. [51], carcass evaluation is one of the most important aspects of broiler production, as it indicates the amount of meat produced. Fik et al. [30] reported that adding 0.5, 1.0 or 1.5% citric acid to the drinking water of broilers had no significant effect on carcass yield or thigh percentage, but the proportion of breast meat was significantly increased in chickens receiving citric acid. The weights of organs such as heart, gizzard, neck, foregut, pancreas, cecum, kidney and large intestine did not differ between the control and citric acid groups. However, the addition of 0.5% citric acid to the drinking water caused a significant reduction in the weights of liver, gizzard and small intestine compared to groups receiving 1.0 or 1.5% citric acid.

A study by Manvatkar et al. [9] showed that the use of coated organic acids improved carcass yield, percentage of evisceration, thigh, breast meat and relative weight of internal organs, but the weight of cut parts such as thigh, wing and back was not different from the control group.

A study by Rehman et al. [35] also showed that the addition of 10, 20 or 30 g/kg of acetic acid did not significantly affect carcass yield, but improved the length and weight of the small intestine. These positive effects could be due to the bacteriostatic and bactericidal properties of organic acids, which improve the health of the digestive tract.

The addition of citric acid at 2.4, 3.2 and 4.0 mg/kg to the diet also had no effect on carcass yield, gizzard weight, liver or heart in 42-day-old broilers [39]. Similarly, the addition of varying levels of acetic acid (1% to 10%) had no significant effect on the weight of internal organs (liver, pancreas, spleen, and small intestine) [52].

Also, the addition of formic acid, butyric acid, or their combination to the diet of broiler chickens had no effect on the percentage of carcass eviscerated, viscera weight, or carcass cuts (except back cut) [53].

Challenges and possible solutions in the use of organic acids in broiler nutrition

Despite the potential of organic acids to improve gut health, increase nutrient absorption, and replace antibiotics, their practical application is accompanied by challenges that may affect effectiveness and cost-effectiveness:

Variations in efficacy: The efficacy of organic acids depends on the type of acid, concentration, age and health of the bird, and diet composition. A suggested solution is to conduct further research to find the appropriate composition and level of organic acids under different rearing conditions. Precision Feeding strategies can also lead to more reliable results.

Reduced palatability: At high concentrations, organic acids can reduce feed attractiveness and reduce feed intake. Suggested solutions:

Use encapsulation technology to mask the taste of acids.

Gradually accustom birds to the taste of acids by gradually increasing the dosage.

High cost: Organic acids, especially in pure or encapsulated form, can be expensive. To address this problem:

Concurrent use of organic acids with probiotics or essential oils can reduce costs and maintain effectiveness.

Furthermore, continued use of organic acids may lead to the development of microbial resistance, similar to the problems seen with the use of antibiotics. This can reduce the long-term effectiveness of organic acids in controlling pathogenic bacteria. Therefore, rotating the use of different types of organic acids in combination with other antimicrobial strategies can help reduce the risk of resistance development.

However, the presence of other antimicrobial compounds may reduce the effectiveness of organic acids. Hence, understanding the chemical reactions between different compounds is of great importance.

Conclusion and Future Prospects

Organic acids have shown their effectiveness as an effective alternative to antibiotic growth promoters in broiler nutrition. Previous findings indicate that organic acids:

have a positive effect on the intestinal microbial balance,

increase growth performance,

improve carcass characteristics,

and

Improves the intestinal flora of broilers.

Organic acids are able to change or decrease the pH of the digestive tract; therefore, they reduce the effect of pathogenic bacteria and increase the growth of beneficial microorganisms. As a result, this process increases the histomorphological characteristics of the small intestine in different parts, followed by better absorption of nutrients.

However, the effectiveness of organic acids is affected by several factors and more studies are needed to establish standardized protocols, doses and application methods that will provide a more complete understanding of the use of these acids and maximize their effectiveness in broiler nutrition.

In addition, future research should also focus on investigating the effect of dietary organic acids on feed palatability in broilers.

Acidifiers play an important role in intestinal health and improve nutrient digestibility. Acidification of the intestine can greatly help eliminate harmful bacteria by breaking down their membrane capsule and creating a suitable environment for beneficial bacteria. #ChitikaAcidifier# consists of a combination of ascorbic, citric and acetic acids, formulated in powder and microcapsules. This product is designed to have the lowest solubility in the initial parts of the digestive tract and its target location is the small intestine.

Chitika Acidifier

Very powerful powdered microcapsule acidifier
The most important beneficial effects of Chitika Acidifier
Providing a suitable place for the growth and reproduction of probiotics
Increasing the beneficial microbial population of the intestine
Increasing the productivity of the bird’s digestive system
Improving the digestion index

The most important benefits of using Chitika Acidifier in poultry

Antimicrobial
Improving the digestibility of nutrients
Improving the health of the digestive system and ultimately the health of the animal
Improving performance in broilers and laying hens
Reducing ammonia production by modifying microbial flora
Improving palatability and stimulating feed consumption
Improving the growth of intestinal microvilli
Strengthening the immune system
Reducing diseases and mortality
Easy to use due to its solid and powdered physical form

Consumption amount: one kilogram per ton of feed consumed Ingredients in Chitika Acidifier: acetic acid, citric acid, ascorbic acid and filler

The most important effects of the product

Providing a suitable place for growth and reproduction Probiotics
Increase beneficial intestinal microbial population
Increase bird digestive tract efficiency
Improve digestion index