Effect of supplemental organic acids on growth performance and gut microbial population of broiler chicken

S Adil, M T Banday, G A Bhat, S D Qureshi and S A Wani

Department of Livestock Production and Management, Faculty of Veterinary Sciences and Animal Husbandry, Sher-e-Kashmir University of Agricultural Sciences & Technology of Kashmir, Shuhama-190006, Jammu and Kashmir, India.
mtbanday5@gmail.com

Abstract

The aim of the study was to evaluate the efficiency of organic acid supplementation as growth promoters in broiler chicken. The study was carried out utilizing 315 Cobb straight run commercial broiler chicks which were randomly assigned into seven groups having three replicates of 15 chicks each. Birds in the control (T₁) group were fed basal diet where as birds in other treatment groups were fed basal diet supplemented with 2% butyric acid (T₂), 3% butyric acid (T₄), 2% fumaric acid (T₄), 3% fumaric acid (T₅), 2% lactic acid (T₆) and 3% lactic acid (T₇).

Results revealed that the birds fed diets supplemented with organic acids had significantly (p<0.05) higher body weight gains. Cumulative feed consumption was decreased (p<0.05) in the groups fed supplemental organic acids compared to control group which had highest feed intake. Supplementation of organic acids improved (p<0.05) the feed conversion ratio (FCR) as against the birds fed basal diet without organic acids. Addition of organic acids to the diets of broiler chicken decreased (p<0.05) the caecal viable and coliform counts compared to the unsupplemented group. The pH value in crop was decreased (p<0.05) in the birds fed organic acid based diets but no effected on caecal pH was observed compared to the unsupplemented birds. Increased (p>0.05) serum protein levels were observed in groups fed organic acid based diet. The length of gastro-intestinal tract (GIT) was significantly (p<0.05) increased in the groups fed supplemental organic acids.

Key words: Broiler chicken, growth, microflora, organic acids

Introduction

Because of the growing concern over the transmission and proliferation of resistant bacteria via the food chain, the European Union (EU) in 2006 banned antibiotic growth promoters to be used as additives in animal nutrition. So there aroused the need for alternative strategies to minimize the risk of spreading antibiotic resistance from animals to humans via food chain. The alternative which has showed some potential in this regard are organic acids. Organic acids and their salts are generally regarded as safe (GRAS) and have been approved by most member states of the EU to be used as feed additives in animal production. Organic acids have growth promoting properties and can be used as alternatives to antibiotics (Patten and Waldroup 1988). The addition of organic acids to the broiler diet reduces the production of toxic components by bacteria and the colonization of pathogens in the GIT (Langhout 2000; Denli et al 2003).  Organic acids may affect the integrity of microbial cell membrane or cell macromolecules or interfere with nutrient transport and energy metabolism causing bactericidal effect (Ricke 2003). Following organic acid feeding, reduction in gastric pH occurs which may increase the pepsin activity (Kirchgessner and Roth 1982) and the peptides arising from pepsin proteolysis trigger the release of hormones, including gastrin and cholecystokinin, which regulate the digestion and absorption of protein (Hersey 1987). Organic acid supplementation have been reported to decrease colonization of pathogens and production of toxic metabolites, improve digestibility of protein and minerals like calcium, phosphorus, magnesium and zinc and also serve as substrates in the intermediary metabolism (Kirchgessner and Roth 1988). The present study was carried on with the objectives to determine the effect of organic acid supplementation on the growth performance and intestinal microflora of broiler chicken.

Materials and methods 

A total number of 315 Cobb straight run commercial broiler chicks were utilized in this study. On arrival chicks were provided with 8% sugar solution and ground maize for first 12 hours. To avoid stress, water soluble vitamins and electrolytes were added to the drinking water for first 3 days. At 7 days of age, birds were individually weighed and randomly assigned into seven groups having three replicates of 15 chicks each. The birds were placed in battery cages ands temperature was gradually reduced from 32 to 20⁰C on day 42. The chicks were maintained on a 24 hours consistent lighting schedule. Proper ventilation was ensured by means of exhaust fans. Birds were vaccinated against New castle and Gumboro’s diseases. Fresh feed and water were provided daily ad libitum. The feeding programme consisted of a starter diet until 21 days and a finisher diet until 42 days of age. All diets for each period were prepared with the same batch of ingredients and all diets within a period had the same composition. The diets were formulated to meet the recommendations of the Bureau of Indian Standards (BIS 1992). The ingredients composition on dry matter (DM) basis of the control diet is shown in Table 1.

Birds in the control group were given diets without additives (T₁). The other six treatment groups were given the same diets as fed to the control groups, but supplemented with 2% butyric acid (T₂), 3% butyric acid (T₄), 2% fumaric acid (T₄), 3% fumaric acid (T₅), 2% lactic acid (T₆) and 3% lactic acid (T₇). After thorough mixing of ingredients, the organic acids (powder form) were mixed in the aforesaid concentrations.

The chemical analysis of feed samples was done as per AOAC (1996). The dietary ingredients were analyzed for crude protein, crude fiber, ether extract and total ash. The body weight of birds per replicate was recorded on individual basis at weekly intervals. Cumulative feed consumption per replicate was also recorded on weekly basis. Feed conversion ratio per replicate was worked out at weekly intervals by taking into consideration weekly body weight gain and feed consumption of respective replicate.    

At the end of feeding trial, six birds per treatment were selected at random and severed at the atlanto-occipital joint. Length of GIT was measured by means of a measuring tape. Intestines were exposed ligated at both sides. The caecal contents were collected aseptically. Samples were weighed (1 gm), transferred to sterile tubes and homogenized with sterile 0.9% normal saline solution (1:1). Then the solutions were mixed on vortex. Serial dilutions of samples were made up to sixth dilution. 0.1 ml of each dilution was poured and spread uniformly on brain heart infusion (BHI) agar for estimation of caecal coliform count and McConkey’s agar for caecal coliform count. Plates were incubated at 37⁰C for 48 hours. Bacterial colonies were counted by pour plate method (Quinn et al 1992). The average number of colonies was multiplied by reciprocal of the dilution factor and expressed as cfu/g of contents.

The pH of the gut contents was determined by using the method of Al-Natour and Alshawabkeh (2005). Ten grams each from crop and caeca were collected aseptically in 90 ml sterilized physiological saline (1:10 dilution) and pH was determined.

Blood samples were collected from the slaughtered birds in non-heparinised tubes. The samples were centrifuged at 3000 rpm for 15 minutes and serum obtained was stored at -20⁰C until analysis. Serum protein levels were determined by auto analyzer using commercially available kits purchased from Accurex biomedical company.       

The data obtained were statistically expressed as means ± standard error and assessed by General Linear Model procedure of SPSS (1997) software considering replicates as experimental units. Duncan’s multiple range test (Duncan 1955) was used to test the significance of difference between means. Differences were considered significant at p≤0.05.

Results and discussion 

The laboratory chemical analysis result of feed ingredients used in formulation of the ration is shown in Table 2. There was no difference in chemical analysis results between the starter and finisher diets.

Cumulative feed consumption was found decreased (p<0.05) in all the groups fed organic acids compared to control group (Table 3).

The reduction in the feed intake might be due to the strong taste associated with the organic acids which would have decreased the palatability of feed, thereby reduced feed intake. Also Cave (1978) reported that propionic acid plays a role in the satiation regulatory system, since intraperitonial injection of the organic acid in broilers suspended intake for 0.5 to 1.5 hours. Similar results were found by Leeson et al (2005) who reported reduction in the feed consumption in groups fed butyric acid based diets compared with the group fed control diet. Chicks fed the diets supplemented with organic acids showed a significant (p<0.05) improvement in the FCR as against the chicks fed control diet. The improvement in FCR could be possibly due to lesser feed intake resulting in increased body weight gain because of better utilization of nutrients in the birds fed organic acids in the diet. These results are in harmony with the reports of Vogt et al (1981) who reported that organic acids improved the FCR in broiler chicken.

Results indicated that the birds fed organic acid based diet had higher (p<0.05) body weight gains compared to unsupplemented group (Table 3, Figure 1).

Figure 1.  Average body weight gain (g) at 6 weeks of age under different dietary treatments

These results are in harmony with Owens et al (2008) who reported that improved body weight gains in broiler chicken fed organic acid supplemented diet. In the present study, highest body weight gains were achieved in the birds fed 3% fumaric acid in the diet followed by group fed diet having 2% fumaric acid. Antibacterial effect of organic acids has been associated with the improvement in the weight gains in broiler chicken by many researchers. Undissociated organic acids pass through the cell membrane of the bacteria and dissociate to form H⁺ ions which lower the pH of bacterial cell, causing the organism to use its energy, trying to restore the normal balance. Whereas RCOO^- anions produced from the acid can disrupt DNA, hampering protein synthesis and putting the organism in stress. As a result the organism cannot multiply rapidly and decrease in number Nursey (1997).

The antibacterial effect of organic acids was also observed in the present study (Table 4) in which significant (p<0.05) reduction in the caecal viable and coliform counts in birds fed organic based diet was recorded.

Similar effects were observed by Owens et al (2008) and Pirgozliev et al (2008) reporting significantly (p<0.05) reduced total viable coliform numbers in the ileum and caecum of broiler chicken due to organic acid supplementation. Gunal et al (2006) also reported that the use of organic acid mixture significantly decreased the total bacterial and gram negative bacterial counts in broiler chicken. Moharrery and Mahzonieh (2005) recorded decrease in E.Coli population in the intestines of broiler chicken with malic acid.

Furthermore, inclusion of organic acids in the diet of broiler chicken has pH reducing properties in various GIT segments of broiler chicken as was observed in the current study (Table 4). The pH value in the crop and caeca was decreased but the values were not significant (p>0.05) in caecum agreeing with the results of Waldroup et al (1995) who reported that the addition of lactic acid at a concentration from 0.25 to 2% or fumaric acid from 0.5 to 2% to broiler diet had no effect on caecal pH. The pH values in the crop and caeca got reduced as the concentration of dietary organic acids increased, but the values were within the physiological pH range. As per Bolton and Dewar (1964) the effects of organic acids down the digestive tract gets diminished because of reduction in the concentration of acids as a result of absorption and metabolism, thus justifying the present findings of significantly decreased pH in the crop and not in the caeca. In this study caecal pH did not decrease much but there was significant (p<0.05) reduction in the number of caecal microflora which could be plausibly due to the reduced entry of pathogenic bacteria from the upper parts of GIT (crop) into the intestines of broiler chicken. The lowered pH is conducive for the growth of favourable bacteria simultaneously hampering the growth of pathogenic bacteria which grow at relatively higher pH. Due to pH reducing properties and direct antimicrobial effect, organic acids might have resulted in inhibition of intestinal bacteria leading to the reduced bacterial competition with the host for available nutrients and diminution in the level of toxic bacterial metabolites as a result of lessened bacterial fermentation resulting in the improvement of protein and energy digestibility, thereby ameliorating the weight gain and performance of broiler chicken. Improved serum protein concentration was also achieved in current study in the birds fed organic acid supplemented feed (Table 4) confirming the growth promoting properties of organic acids.

Apart from antimicrobial and pH reducing effect, organic acids have beneficial effect on the intestinal mucosa of broiler chicken as well. Nutrient absorption in gut occurs from the intestinal mucosa and hence, manipulation thereon may improve the nutrient utilization [Bradley et al (1994); Savage et al (1996); Pelicano et al (2005)] and consequently growth performance. The beneficial effect of organic acids on the GIT tract was also observed in the present study in terms of increased length of GIT (Table 4) as was observed by Denli et al (2003) who reported that organic acids resulted in remarkable increase in the intestinal weight and length of broiler chicken. These results could be attributed to the fact that organic acids have direct stimulatory effect on the gastro-intestinal cell proliferation as was reported by other workers with short chain fatty acids. The short chain fatty acids are believed to increase plasma glucagon-like peptide 2 (GLP-2) and ileal pro-glucagon mRNA, glucose transporter (GLUT2) expression and protein expression, which are all signals which can potentially mediate gut epithelial cell proliferation Tappenden and McBurney (1998). Le Blay et al (2000) and Fukunaga et al (2003) also reported that short chain fatty acids can accelerate gut epithelial cell proliferation, thereby increase intestinal tissue weight, which will result in changes of mucosal morphology.      

In conclusion, organic acid supplementation had positive effect in improving the performance in terms of body weight gain and FCR, which was possibly due to the antimicrobial activity, reduction in the pH value of various GIT segments and beneficial effect on serum protein concentration and gut mucosa of broiler chicken.

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Received 21 February 2010; Accepted 14 December 2010; Published 5 January 2011

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