Introduction
The poultry production systems around the globe have used antibiotics at sub therapeutic levels for years as growth promoters for better performance of chicken, but due to the rising concern of development of antibiotic resistance and reports of cross resistance followed by subsequent ban of antibiotic usage in certain regions of the world it has become imperative for some time now to search for alternatives to antibiotics which could match their performance. In the ongoing quest acidifiers and phytogenic growth promoters specially, essential oils have shown promising results as alternatives and various commercial products are now available in the market in each category. Addition of organic acids in feed have shown improved performance of chickens in layers where use of Phenylacetic acid linearly improved the performance of laying hens. combine the usage of both organic acids and essential oils could suitably prove to be an alternative of antibiotic growth promoters in poultry as well as swine feeding. While organic acids which been beneficial as feed additives are generally short chain fatty acids (SCFA) having carbon C1-C4 and Medium chain fatty acids (MCFA) having carbon C4-C12 and have earlier been used as feed preservatives, essential oils are extracts obtained from herbs after certain procedures. Antimicrobial action of both of them in the gut and modification of gut micro flora in favour of the concerned animal to inhibit the growth of detrimental microbes of the micro biome to subsequently increase the nutrient digestibility and decrease incidence of diseases.
The various forms in which the organic acids are used in the feed are as follows
1. Added to the poultry feed in a solid form. This fights mold development in the feed and reduces the pH in the birds’ crops.
2. Sprayed onto the poultry litter. This attacks the bacteria that facilitate the breakdown of uric acid, limiting the amount of ammonia releases.
3. Injected into the water to kill bacteria, facilitate chlorine in killing bacteria and lowering the pH in the birds’ crops.
The mode of action of organic acids
In poultry is mainly antimicrobial, a key activity is reduction of stomach PH. Organic acids have been found to be both bacteriostatic and bactericidal. As undissociated organic acids are lipophilic, they can cross the cell membrane of Gram-negative bacteria, such as Salmonella. The fact which is important is when it enters inside the cell of the bacteria the higher cytosolic pH causes the acid to dissociate, releasing hydrogen ions, which consequently reduces the intracellular pH and results in accumulation of hydrogen ions in the cell. This eventually results in the depression of the enzymatic machinery of the cell and it starts to pump proton out in order to reestablish the normal pH levels even at the cost of energy expenditure via proton pump mechanisms. Over a period of exposure to an organic acid, this can be sufficient to kill the cell.
Effects Beyond Antimicrobial Activity
There are effects beyond it which can be broadly categorized as, first, the ones produced due to effects of acidification such as enhanced digestive enzymatic activity, increased microbial Phytase activity, and increased pancreatic secretion. Secondly, there is evidence of increased growth of the gastrointestinal mucosa in the presence of organic acids, particularly fatty acids such as butyric acid. The organic acids improve the villus height in the small intestines and also have a direct stimulatory effect on the gastro-intestinal cell proliferation, the histological changes in small intestines probably had increased the intestinal surface area, facilitating the nutrient absorption to a greater extent and, thus boosted the growth promoting effect of organic acid supplementation. Third, improvement in digestibility have been reported and higher metabolizable energy in broilers fed 0.5 to 1% fumaric acid.
Effects of Organic Acids on Performance of Chickens
- Tartaric, Lactic and Malic acid: Improvement in weight gain on broilers.
- Fumaric and Sorbic acid: Improved feed efficiency in broilers and layers.
- Buffered propionic acid: Increased dressing percentage and reduction in abdominal fat.
- Butyric acid: Maintain beneficial microflora.
EO blend 300 Broiler Decreased intestinal Clostridium, but no effect on total organisms, Kırkpınar et al [26]
EO 100 Broiler Increase in the mean numbers of bacterial species in the ileal content Amerah et al. [27]
EO blend 1,000 Broiler No change in cecal and fecal Coliforms, Lactobacillus, C. perfringens and total anaerobes Cross et al. [28]
Oregano EO 300-1,200 Broiler Decreased cecal E. Coli but no effect for 1200 ppm; no effect on cecal Lactobacilli Roofchaee et al. [29]
EO 125 Broiler No change in cecal total bacteria, Lactobacilli, Enterococci, Coliforms or Salmonellae colonization. Hong et al. [30]
EO blend 150-500 Broiler Decreased crop Salmonella but no effect for 150 ppm; no effect on cecal Salmonella Alali et al. [31]
Thymol/EO 30 Broiler Increased cecal Lactobacilli and decreased Coliform but no effect on crop and ileum Ginnenas et al. [35]
Oregano EO 300 Broiler Lower bloody diarrhea, lesion score and oocyst numbers compared to control (E. tenella challenge) Ginnenas et al. [49]
Oregano 330 Broiler Decreased C. perfringens counts in cecum Waldenstedt et al. [50]
EO blend 100 Broiler Reduction of C. perfringens concentration in the jejunum and colon Mitsch et al. [51]
Plant extract 100 Broiler Reduction of E. coli, C. perfringens and fungi and increase of Lactobacillus Jamroz et al. [52]
Oregano EO 0.5-1.25 Broiler Oregano EO exhibited a strong bactericidal effect against Lactobacilli at both doses tested Horošová et al. [53]
EO blend 100 Broiler Increased ileal Lactobacillus counts coupled with decreased E.Coli counts Rahimi et al. [54]
EO 500 Broiler Decreased cecal Staphylococci, Lactobacilli and Enterobacteriaceae Placha et al. [55]
EO blend 25/50 Broiler Decreased ileo-cecal E. Coli, and no change in Lactobacilli
Essential oils in poultry nutrition
Phytogenic Feed Additives (PFA) or phytiobiotics or herbal feed additives which represent a wide range of bioactive compounds obtained from plants are an exicting alternatives for antibiotic growth promoters which have been researched for more than the last 20 years. Essential oils are volatile aromatic lipophilic compounds derived by cold expression or by steam or alcohol distillation of different parts of plant materials. Most of the Essential oils are safe to use as feed additives but are volatile resulting in evaporation and inconsistency in the concentrations also pungent at times resulting in feed refusal and therefore encapsulation of such oils can be a viable alternative. Various Essential oils (thymol, carvacrol, cinnamaldehyde, and eugenol, have been used individually or as blends to improve animal health and performance.
Effects of Essential Oils on Overall Performance of Chicken
Different effects have been shown by different essential oils like better feed efficiency and better resistance to coccidiosis and necrotic enteritis were used with inclusion level. The effect of different concentrations of ginger root powder and its essential oil on growth performance, serum metabolites and antioxidant status in broiler chicks under heat stress has been reported. Improved nutrient absorption as shown by many studies attributed to the increased salivation, bile and enhanced enzymatic activity. Decreased numbers of pathogenic bacteria in the gut may improve the ability of epithelial cells to regenerated villus and thus enhance intestinal absorptive capacity. Growth enhancement and better performance of the chicken through the use of phytobiotic Essential oils is probably the result of the synergistic effects among complex active molecules existing in phytogenics. Essential oil combination from wild herbs increased the BW and improved FCR of broilers.
Conclusions
Organic acids and Essential oils are bound to play an important role as growth promoters to replace the antibiotics used so far in the production systems. Thymol, carvacol, cinnamon and eugenol have been the phylogenetically active essential oils that have found more way in additives and these have shown to have positive effects on the performance parameters, gut microflora, gut morphology, immune system and disease control and the overall effects are a result of the combination of all of the individual effects. Although several studies have shown that individually both of these additives have shown improvement in the performance parameters but a realistic additive that could be developed to match the performance of antibiotics could be expected by use of both of them in the correct combination that can exploit the synergy between the two and further studies could reveal the mechanism involved behind the synergy.
Dr. Anil Kumar and Dr. Pallabi Das*
M.V. Sc. Scholar, Department of Livestock Production Management
Ph.D. Scholar, Department of Animal Nutrition
Rajasthan University of Veterinary and Animal Sciences, Bikaner (Rajasthan)
*Corresponding author: pallabidas066@gmail.com
