Effects of Essential Oils and Encapsulated Butyric Acid on Growth Performance, Intestinal Microflora and Serum Lipid Profile of Japanese Quails

Antibiotics as growth promoters (AGPs) have been extensively used at sub-therapeutic levels in poultry production to prevent diseases and promote growth performance. However, the persistent use of antibiotics can increase antibiotic-resistant bacteria and antibiotic residue accumulation in the animal products as well as potentially transferring resistant strains to humans through the food chain (Jazi et al., 2018a). Consequently, the poultry industry has been forced to seek alternatives to AGPs in poultry feeds. Essential oils (EO) extracted from aromatic plants as feed additives, have demonstrated benefits on growth performance, as well as antibacterial and antioxidant effects for birds (Du et al., 2015). In addition, some studies have shown that the use of EO reduces serum cholesterol in broiler chickens (Chowdhury et al., 2018). Butyric acid (BA), a short chain organic acid, has shown beneficial effect in increasing the production of mucin and antimicrobial peptides which enhances the development of intestinal epithelium and defense barriers (Fernandez-Rubio et al., 2009). Encapsulated organic acids which are active in the entire digestive tract have a higher efficacy than free organic acids in reducing pathogen bacteria proliferation in the gastrointestinal tract (Levy et al., 2015). The present research was designed to determine the efficacy of EO, encapsulated BA, and the synergistic effects of the 2 additives (MIX) on growth performance, intestinal microflora and serum lipid profile of Japanese quails.

Three hundred and sixty one-day-old healthy Japanese quail chicks were obtained from a local hatchery, weighed and randomly allocated to 1 of 4 experimental groups with 6 replicate pens of 15 birds each with an initial body weight of 10.53 ± 1.17 g. The experimental diets were as follows: 1) basal diet as control, (CON), 2) basal diet + 300 mg essential oil/kg of diet (EO; CRINA^® Poultry; DSM Nutritional Products Ltd., Switzerland, containing 29% active components such as thymol, piperine, and eugenol), 3) basal diet + 500 mg butyric acid/kg of feed (BA; ButiPEARL; Kemin Industries, Herentals, Belgium, including 50% butyrate salt), and 4) basal diet + 300 mg/kg EO and 500 mg/kg BA (MIX). Nutritional requirements of the Japanese quails were adopted from National Research Council (NRC, 1994) tables. The rearing conditions and lighting, and temperature program were based on those described by Jazi et al. (2018b). Feed intake (FI), body weight (BW) gain, and feed conversion rate (FCR) were recorded for d 1-21, d 21-35, and d 1-35 periods. Microbiological examinations were carried out according to the method described by Jazi et al. (2018a, b). Briefly, enumeration of lactic acid bacteria (LAB), coliforms and total anaerobic bacteria (TAB) were carried out on de Man Rogosa and Sharpe agar, violet red bile agar and plate count agar, respectively. To measure serum lipid profile, at d 35, 12 birds from each experimental group were randomly selected and blood samples were collected from the wing vein (Jazi et al., 2018b). All data were subjected to one-way ANOVA as a completely randomized design using the GLM procedure of SAS (SAS, 2003). Tukey’s HSD test was used to make pairwise comparisons between means, where appropriate. Statistical significance was declared at P < 0.05. Data represent means of 6 replicates per treatment.

For the d 1-21 period, birds fed the diets supplemented with EO, BA, and particularly MIX had greater BW gain and lower FCR than the birds on the CON diet (Table 1; P < 0.05). Likewise, for the d 21-35 and the total growth period, BW gain was greater and FCR was lower in birds fed the diets supplemented with EO and MIX compared to the birds fed the CON and the BA diets (P < 0.05).

However, no differences were observed in feed intake of birds. The LAB population was greater in the ileum and caeca of birds fed the diets containing EO, BA, and MIX when compared to CON (Table 2; P < 0.05). Also, birds fed the additives had a lower count of coliforms in the ileum and caeca content (P < 0.05).

Concentrations of the total cholesterol and the LDL-cholesterol in the serum of birds fed with EO, BA or MIX were lower than the CON birds (Table 3; P < 0.05). Experimental diets had no effect on the concentrations of triglycerides, HDL and LDL-cholesterol of birds.

The results of the current study showed that all the experimental diets improved the growth performance of birds compared to the CON diet. However, birds fed the MIX diet had the greatest BW gain and lowest FCR among the experimental groups, which indicates the synergistic effect of the feed additives used in the present study. Similarly, Levy et al. (2015) reported that supplementing encapsulated BA to the diet improved BW gain and FCR compared to the control. Jazi et al. (2018a) have also reported that BA supplementation improved the growth performance of broilers challenged with Salmonella. In a recent study, however, it has been reported that the use of non-encapsulated organic acids has no effect on the growth performance of quail chicks (Jazi et al., 2018b). Lack of growth response to the added free organic acids is probably due to quick absorption of these acids in the upper gastrointestinal tract such as the crop, while the encapsulated organic acids can reach the hind gut (Levy et al., 2015). The positive effects of BA supplements on bird’s growth performance is likely due to their ability to lower the pH of the gastrointestinal tract and increase the proliferation of beneficial microbes such as Lactobacillus (Jazi et al., 2018a). Our results are in line with the results of various studies showing the benefits of the use of EO in improving the growth performance of birds (Jang et al., 2007; Park and Kim. 2018). Improved growth performance of the birds can be due to the stimulating effects of EO on digestive enzymes, antibacterial activity, balancing the microbial flora of the digestive tract, and improving the intestinal morphology (Jang et al., 2007; Chowdhury et al., 2018).

Dietary supplements resulted in an increase in caeca lactic acid bacteria counts and a decrease in ileum and caeca coliforms counts. Du et al. (2015) reported that EO (thymol and carvacrol) exhibited a strong antibacterial activity against gram-negative bacteria such as E. coli, Salmonella strains, and C. perfringens. Park and Kim (2018) demonstrated that the addition of EO to broiler diets increased Lactobacillus counts and decreased E. coli populations in the ileum. As a potential mechanism of antimicrobial activity, the EO may stimulate mucus secretion into the intestinal lumen and create a disturbance to the bacterial cell membrane through disintegrating the outer membrane causing leakage of intracellular materials (Du et al., 2015). Similarly, Jazi et al. (2018a) showed that feeding encapsulated BA in broiler chicks increased Lactobacillus and decreased Bifidobacterium counts in the caeca. Organic acids provide the optimum conditions for the growth and proliferation of beneficial bacteria through increasing the acidity of the gastrointestinal tract (Jazi et al., 2018a). Beneficial bacteria will consequently reduce the pH of the gut by producing short-chain fatty acids, creating a natural defense against pathogenic bacteria.

In the present study, concentrations of total cholesterol and LDL-cholesterol of birds fed the experimental diets were lower than the control group. Recently, Chowdhury et al. (2018) reported that feeding diets containing EO reduced the serum concentrations of cholesterol and LDL-cholesterol in broiler chicks. Lea et al., (2003) have shown that EO have inhibitory effects on 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase enzyme activity. This enzyme is responsible for the synthesis of liver cholesterol. In addition, the increase in LAB reduces the intestinal pH and deconjugated bile salts which impairs the intestinal absorption of bile salts and therefore increases the fecal excretion of bile salts. As a result, the liver turns a greater amount of cholesterol to bile to reconnect the intestinal-liver cycle of bile salts. Cholesterol concentration, therefore, is reduced in the blood and tissues (Jazi et al. 2018b).

The results obtained in the present research indicate that the use of EO, with or without BA improves growth performance, increases caeca lactic acid bacteria counts, and reduces ileum and caeca coliform counts as well as serum cholesterol level. In conclusion, based on the synergistic effects of EO and BA, the 2 additives could be considered as an alternative to antibiotics.