Amongst the most significant challenges plaguing the poultry industry mostly boilers need more focus in order to minimize pathogen effects on human and animal health (
Marshall and Levy, 2011;
Moyane et al., 2013; Calicioglu et al., 2019).
Antibiotics, antifungals, antivirals, antimalarials and anthelmintics, for example, have raised levels of tolerance in bacteria, parasites, viruses and fungi (
FAO, 2017). Antibiotic growth promoters have been used in broilers to optimize live weight and feed efficiency (virginiamycin, linomycin, sacox, avilamycin, flavomycin and others)
(Diaz Carrasco et al., 2019). However, there are consumer fears that their addition in the feed may promote resistant strains of pathogens against those antibiotics (
Paiva and McElroy, 2014;
Dittoe et al., 2018). Antibiotic growth promoters such as avoparcin, enrofloxacin and tylosin triggered the production of a resistant pathogen in the human population through the consumption of animal-derived food
(Bozkurt et al., 2008; Cogliani et al., 2011; Ao et al., 2012). Furthermore, the use of antibiotic performance enhancers (APE), as well as the clinical use of anticoccidials and chemotherapy, has been shown to be particularly harmful to birds. Since 2006, the European Union has prohibited the use of antibiotics as growth promoters and North America has followed suit. This is due to the significant danger of antimicrobial resistance (
Khan and Iqbal, 2015;
Pritchard, 2016).
Alternative forms of growth promoters for poultry, such as organic acid, have been investigated systematically. These alternatives provide some adequate essential and non-essential elements to stimulate growth (
M’Sadeq et al., 2015). Furthermore,
Mohyla et al., (2007) observed that the usage of citric acid might promote the growth of broiler chickens while simultaneously decreasing mortality. Citric acid supplementation has been explored to be an effective feed additive for broiler growth (
M’Sadeq et al., 2015,
Dittoe et al., 2018, Al-Amri and Al-Jasham, 2019). Thus, the chemical properties of citric acid enable it, to be supplemented in water for chickens and pigs, to enhance growth (
M’Sadeq et al., 2015). There is limited information on properties of citric acid along with its nutritive potential and utilization as feed additive in chickens feed components that is comprehensive in South Africa. Thus, the purpose of this review is to raise awareness about the nutritional value and potential growth promoter properties of citric acid as a source of growth promoter for chicken.
Description of citric acid
The citric acid found in citric fruits is a weak organic acid
(Islam et al., 2008). Citrus fruits (lemons, oranges, grapesand so on) are categorized as acid fruits because they contain sufficient amount of citric acid
(Max et al., 2010). Citric acid is an extremely flexible organic acid that is frequently applied in the drug industry
(Islam et al., 2008). Pigs and chickens have widely given citric acid as an organic acid supplement (
Kim et al., 2015,
Lakshmi and Sunder, 2015,
Diaz et al., 2019). Haščík et al. (2019) reported that citric acid is mostly utilized as an acidifier and flavouring ingredient. This organic compound is a natural preservative that is frequently used to give food and soft drinks an acidic or sour taste (
Pelletier and Lawless, 2003;
Bagal et al., 2016). It exhibits adequate antimicrobial activity to inhibit bacterial spoilage while also reducing harmful bacteria in the gastrointestinal tract (example, E. coli.)
(Archana et al., 2019) and ultimately improves the growth rate of different animal species to an extent comparable to antimicrobial growth promoters (
Llor and Bjerrum, 2014).
Citric acid as a growth promoter
Early therapeutic acidifier exposure in birds can elicit adaptive response, minimizing the antimicrobial activity and as a result, enhancing the birds’ development efficiency
(Islam et al., 2008). In order to limit the economic losses due to heat pressure, it is therefore essential to supplement or expose the use of acidifiers in the initial phase instead of the growing one.
Archana et al., (2019) indicated that decreased pH in the intestines with added citric acid may regulate the release of enzymes such as pepsin and phytase that have an impact on the gastrointestinal tract. Citric acid promotes the utilisation of protein and certain minerals
(Nourmohammadi et al., 2011; AL-harthi and Attia, 2015). The lower pH makes the gastro-intestinal tract (GIT) conditions unfavourable to pathogenic bacteria and stimulates the growth of ‘healthy’ bacteria, leading to high digestion and utilization within the GIT
(Mansoub et al., 2011).
Effect of citric acid on growth performance
Effect of citric acid on feed intake
The citric acid in high doses reduces feed palatability, while low concentrations enhance feed consumption and thus increase growth in avian species (
Haščík et al., 2019). This might be due to the fact that lower pH leads to a simultaneous increase in favorable bacteria and a substantially higher pH, impede the development of pathogenic bacteria. The inclusion of 0.25 per cent citric acid in the mesh diet reduced consumption (
Mohammed, 2018).
Mohammadagheri et al., (2016) discovered that citric acid (1.0 per cent) had no influence on feed consumption. A similar effect was reported when 0.5 per cent citric acid was added to the diet (
Islam, 2008;
Ghazalah et al., 2011). Moreover,
Rahman et al., (2018) revealed that the inclusion of 0.75 per cent citric acid to the broiler diet had a significant positive impact on the broilers’ feed consumption. This could be because an acidic gastric environment promotes peptide-2, which may aid glucose and protein absorption.
Moghadam et al., (2006) reported that supplementing broilers with citric acid (1.5 per cent and 3.0 per cent) had a positive effect on feed intake and consumption. A study performed by
Atapathu and Nelligaswatta (2005) found that broiler chicks fed a rice-based diet containing 2.0 per cent CA increased their feed consumption significantly
(Ao et al., 2009). Citric acid supplementation in the diet had no effect on feed intake in broilers at 21 and 42 days of age (Waseem
Mirza et al., 2016).
Effect of citric acid on body weight gain
Nezhad et al., (2007) observed that inclusion of citric acid (0.0, 2.5% and 5%) in water showed a significant effect in broilers on maize soyabean meal-based diet and improved the live weight gain and the effect of the interaction between CA and microbial phytase showed significant improvement on live weight gain (
Islam et al., 2008;
Islam, 2012;
Kalafova et al., 2014; Shah et al., 2018). Furthermore, the administration of citric acid (0.3, 0.5 and 0.7 per cent) exhibited the best results in terms of improvement in live weight increase when compared to other treatments
(Shen et al., 2005; Islam et al., 2008;
Mohammed, 2018). Improved performance can be attributed to competitive inhibition of food-borne pathogens, increased nutrient uptake, growth and feed effectiveness and a decrease in viable bacterial cells. Adding CA, ascorbic acid and vitamin D3 to a low calcium diet in broilers increased their body weight by 18 percent, but they had insignificant growth performance when they were fed CA (1 and 2 per cent) with rice by-product-based diets, according to
Afsharmanesh and Pourreza (2005). This distinction may be attributable to the fact that the birds’ response to organic acid supplementation is dependent on the kind and concentration of the acids, the content of meal, the animals’ age and health status
(Jensen et al., 2003).
Effect of citric acid on feed conversion efficiency
Organic acid addition is a significant step toward greater efficiency without the use of drugs, which may leave impurities in the meat and increase the danger of antimicrobial resistance
(Kim et al., 2015). The reduction in pH in the GIT promotes a variety of enzymes, including pepsinogen and other zymogens, by attempting to bring the extracellular pH closer to the optimum value required for optimal action (
Afsharmanesh and Pourreza, 2005). Steadily increasing pepsinogen activity results in increased proteolysis, which produces a variety of peptides that trigger the release of cholecystokinin and gastrin
(Adil et al., 2010; Samanta et al., 2010). The phenomena of supplementation with citric acid (0.3 per cent) ensures the effective broiler chick feed conversion in comparison to those on a control diet
(Shen et al., 2005). This could be due to a direct effect of the crop’s reduced pH, as the enzyme operates optimally at a pH of + 4.5. Numerous trials demonstrated a similar effect, with feed conversion efficiency increasing on diets supplemented with three different concentrations of citric acid (0.0, 2.5 and 5.0 per cent), as well as a significant impactof the variety of citric acid and microbial phytase on feed conversion efficiency in broilers
(Nezhad et al., 2007; Islam., 2012;
Haq et al., 2017). Additionally,
Kopeck et al., (2012) found that treatment with CA (0.25 per cent) enhanced the feed conversion ratio in broilers. However, the findings are contrary to the study by
Mohammed (2016) who observed no effect with the supplementation of CA (0.25%).
Atapattu and Nelligaswatta (2005) concluded that supplementation of citric acid (1.0 and 2%) has no effect on feed conversion ratio in broiler chicken-fed rice by product-based diet. This variation could be attributed to the introduction of acidic environments to gut, which triggers the release of pepsin, gastrin and cholecystokinin, which together play important roles in feed conversion and hence improve growth performance
(Hayat et al., 2014).
Effect of citric acid on body linear measurements
Mohammed (2016) noted that using citric acid as a supplement for broilers boosted back fat and had no effect on breast meat yield in terms of weight. Acidification had no influence on breast, thigh, or giblet weight
(Haq et al., 2014). The head, wing, back, thigh and breast showed the most improvement
(Islam et al., 2008). Mohammed (2018) found that adding citric acid to mesh diets improved the thigh, breast, back, wings, head, shank and skin the most. This contrasts with
Kopecký et al., (2012) assessment that the carcass yields, percentages of breasts and thighs and average abdominal fat weights with citric acid are not affected. This contrast may be due to nutrition, location and various breeds used.
Effect of citric acid on digestibility
All modifications to the GIT will have an impact on the digestion and nutrient utilization of the diet. Citric acid degrades the structure of crude fiber, increasing the susceptibility of crude protein and comparable phytate to enzymatic digestion and hence nutrient digestibility (
Lückstädt and Mellor, 2011). Citric acids do not have any residual or detrimental residue in meat products, as well as the lack of any environmental impact contributing to microbial resistance, as is the case with antibiotics.
Vargas-Rodriguez et al., (2002), Ao et al., (2009) and
Haq et al., (2017) discovered that 2 per cent citric acid in the broiler feed improves DM, CP and neutral detergent substance absorption. Moreover,
Ghazala et al., (2011) discovered that providing 2% citric acid to broiler ration improved crude protein (CP), ether extract (EE), crude fiber (CF) and nitrogen-free extract (NFE). Nonetheless,
Mohammadagheri et al., (2016) found that supplementing broilers with citric acid (1.0%) had no effect on digestion. These could be attributed to management techniques and breed, physiological age, different diet and citric acid dose which ultimately change the gastrointestinal pH thus resulting in poor absorption of nutrients and utilization these indirectly affect digestion. Dietary salinity promotes gut proteolysis and digestion
(Cogliani et al., 2011). Broilers added citric acid had longer and thicker villi than controls and thus a better digestive and feed absorbance efficiency
(Abdel-Fattah et al., 2008). Citric acid at (4 to 6%) added to broiler water, resulted in lower crude protein (CP) utilization is lower than that of control (
Islam. 2012;
Nourmohammadi and Khosravinia 2015). Furthermore, CA supplements of 1.0 and 2.0 per cent improved P and CP utilization in broilers
(Atapattu et al., 2005; Ghazalah et al., 2011; Ragab et al., 2012; Shah et al., 2018). Optimized digestive and absorptive abilities of chickens fed organic acid-supplemented diets have been extensively demonstrated and it can thus be concluded that organic acids have a beneficial influence on nutrient utilization of the birds, increasing overall flock effectiveness and efficiency.
Limitation of citric acid in chickens
The limitation to the use of citric acid as an organic growth promoter is that higher doses of organic acid might cause harmful effects in the animal and it could be detrimental for the birds as well (
Hajati, 2018). Moreover, a higher dose affects the performance of the broiler (
Lückstädt and Mellor, 2011). Various parameters, such as dietary contents, proximity to feeding and/or drinking, environmental impacts, other management techniques and even the individual bird itself; breed, physiological age and health status, can all have an impact on the outcomes. Furthermore, most of the tests using organic acids as additive in broiler feeds were carried out under less stressful conditions, which could reflect why the results were uneven.
