Review of the use of organic acids in laying hens diets

Introduction.

The poultry sector is constantly looking for new additives to improve feed efficiency, health and animal welfare. Moreover, consumer demand asking for environmental sustainability pushes farmers to explore new scenarios to maximize the benefits of production.

Feed efficiency is linked very closely to the cost of poultry production, since compound feed occupies a privileged place in the accounts on the one hand, and on the other, pressure from consumers (who demand quality food) requires innocuous and safe food as well as sustainability over time⁽²⁾.

Organic acids and their salts inhibit bacterial growth in feed and consequently preserve the microbial balance in the gastrointestinal tract of animals. In addition, by modifying the pH of the intestine, organic acids also improve the solubility of ingredients, and the digestion and absorption of nutrients ⁽¹²⁾. For example, managing the nutrition of laying hens strategically, it is possible to prevent osteoporosis ⁽⁷⁾, a recurring evil in modern production of eggs for human consumption.

There are about 60 types of organic acids (OA) including lactic, citric, formic and fumaric acids, all of which have different modes of action, different locations or sectors, although the most important role of an organic acid is to reduce the pH in the stomach and intestine ⁽⁴⁾. This review will describe the different ways in which we can use organic acids to bring our poultry production to a sustained efficiency and sustainability over time, offering quality products for consumers that demand high quality.

Organic acids.

Organic acids have been the subject of study as a tool to reduce pathogenic bacteria in poultry production⁽²⁾. Due to the biochemical characteristics of these acids, they penetrate the cell membranes and decrease intracellular pH of pathogenic bacteria. This eliminates the bacteria by means of a metabolic disorder in the level of energy that leads to exhaustion. Thus, it slows down the metabolism of the cell membrane, and reduces the outlet of fluids and the obstruction of the use of nutrients ^{(4, 11)}.

Griggs et al ⁽²⁾ compared chickens receiving diets with and without acidifying (a blend of formic and propionic acid) and an improvement was observed in the performance of those receiving the blend of acids as opposed to those who did not receive it. In relation to this research, Van Immerseel et al ⁽¹¹⁾ reported significant results in the reduction of Salmonella enteritidis in the cecum and internal organs of chickens fed with organic acids (caproic acid).

They are also used to preserve feed in order to prevent the proliferation of pathogenic microorganisms, added to additives used to control fungi and bacteria in the preparation of animal feed ⁽⁴⁾. Van Immerseel et al ⁽¹¹⁾ informs that when a commercial mixture of formic and propionic acid was added to a chicken feed contaminated with high doses of Salmonella Typhimurium, it generated a large decrease (more than 1,000 times) in the viability of this bacterium during 7 days.

Another point to note is the effect that the addition of organic acids has in feed for birds, reducing gastric pH. This reduction accelerates the conversion of pepsinogen to pepsin which results in an improved rate in the absorption of protein, amino acids and minerals.

But in the case of Salmonella the most important thing to consider is the prevention of the colonization of this bacterium. Once the infection is established, it is very difficult to fight this microorganism by treating feed with organic acids.

Treatments with simple organic acids, e.g. formic or propionic, and unprotected acids, have shown no effect on the reduction in Salmonella colonization in the cecum of chickens. Instead the use of a mixture of organic acids and protected granules decreased the viability of the bacteria dramatically, demonstrating the associative and synergistic effect between different acids, such as formic, propionic, butyric and sorbic.

Shell quality and rationale for the use of organic acids.

The quality of the egg shell is one of the most important factors to consider in the poultry industry. It has a direct influence in the profitability of production and affects incubation.

A high resistance to breakage and the absence of shell defects are essential to prevent the entry of pathogenic bacteria such as Salmonella sp. inside the egg ⁽¹⁰⁾. Egg production is a direct parameter that helps us determine whether or not to use an additive.

Modifying intestinal pH with organic acids ⁽¹²⁾ results in an improvement in the solubility of the ingredients (as we mentioned above), digestion and absorption of nutrients. This generated an increase in egg production at the beginning (24th -28th weeks) as well as the extension of the peak period (34th to 38th weeks), in contrast to animals that received no feed with organic acids.

The addition of medium-chain fatty acids (MCFA) has a positive effect on the quality parameters of the egg shell. Shell resistance to breakage decreases with age in hens ⁽¹⁰⁾, but the use of these feed additives helps restore it. This positive effect may probably be due to an increase in the availability of Ca and P, due to the decrease in pH (due to acidifying) in the upper intestinal tract and the stimulation of the length of the microvilli.

This was demonstrated by Swiatkiewicz ⁽¹⁰⁾ when he fed high production hens with MCFA and evaluated the results in egg laying between weeks 46 and 70, concluding that there were positive effects in these quality parameters.

Positive Association between P and Ca organic acids.

Phosphorus is essential for the growth of poultry, in particular for bone development. Traditional diets of birds are based on corn and soybeans, with a high content of P, but availability for absorption is low.

On the other hand, sustainability (as a key factor) is increasingly important for future generations and the large amount of P (in diets with corn and soybean) but low availability makes this combination very unfavorable for the environment around us. This works against the current production systems, which tend to be increasingly intensive; this generates health problems which bring about low productivity, pale colors in the shell and lower resistance to breakage ⁽⁴⁾.

Using a blend of organic acids (lactic, citric, propionic and formic), as reported by Park⁽⁴⁾ in an trial, improved productivity of chickens and showed better values in egg quality parameters (strength, yolk color and shell quality). This happened regardless of the values of P used in the evaluation (0.3% and 0.4% of available phosphorus), concluding that in spite of lower P levels, the results were positive.

As regards bone quality (in the tibia) in older high producing laying hens, positive effects were also observed when dietary organic acids were incorporated. This was due to improvement in the absorption of Ca and P (increased availability) due to the decrease in pH ⁽⁷⁾ and the increase in the length of villi (as mentioned above). In addition to this, Özek⁽³⁾ later concluded that the decrease in viscosity is a factor which also enhances nutrient availability.

Nevertheless, in this last respect, it is important to emphasize that more research is necessary to conclude that there is a successful relationship between viscosity and organic acids, as Özek stated ⁽³⁾.

Conclusions.

As was noted in all the data collected in this review, the addition of organic acids in diets of laying hens has a positive effect on production.

Both as regards health, nutrition and the environment, results obtained by the use of these additives favor the use thereof.

The effect of the entry of pathogens into the egg can be devastating at the time of incubation, for example, and that is why the quality of the egg shell needs to be optimal. Organic acids have antimicrobial activity against Salmonella, which makes them a good alternative to antibiotics (regulations in many countries ban the use of ATB). But at the moment of making a choice, it is necessary to choose a blend of acids, so that the synergy enhances each instead of a simple combination of organic acids.

The reduction in pH in the upper intestine favors solubility, digestion and increases the absorption of nutrients. This demonstrates a positive effect in the efficiency to digest proteins, amino acids and minerals (Ca and P, for example) achieving in this way higher productivity in animals, due to the increase in the amount of eggs, improved animal welfare (cage fatigue) and less environmental pollution of nutrients like P and N (associated with greater cost savings due to decreased excretion of these nutrients consequence of the higher absorption levels).

Finally, it is necessary to conduct more research on the use of medium-chain fatty acids (MCFA) because experiments conducted so far are not conclusive.

It would also be interesting to establish a line of research for the interaction between carbohydrases enzymes and organic acids in relation to the viscosity in the gastrointestinal tract of animals

Bibliografía.

1) Chowdhury R., Islam K.M.S., Khan M.J., Karim M.R., Haque M.N., Khatun M., Pesti G.M., 2009. Effect of citric acid, avilamycin, and their combination on the performance, tibia ash, and immune status of broilers. Poultry Sci. 88, 1616-1622

2) Griggs, J. P., Jacob, J. P. 2005. Alternatives to antibiotics for organic poultry production. J. Appl. Poult. Res. 14:750–756

3) Özek, K., Wellmann, K.T., Ertekin, B., Tarim, B. 2011. Effects of dietary herbal essential oil mixture and organic acid preparation on laying traits, gastrointestinal tract characteristics, blood parameters and immune response of laying hens in a hot summer season. Journal of Animal and Feed Sciences, 20, 575–586

4) Park, K. W., Rhee, A. R., Um, J. S., Paik, I. K. 2009. Effect of dietary available phosphorus and organic acids on the performance and egg quality of laying hens. J. Appl. Poult. Res. 18 :598– 604

5) Rafacz-Livingston, K. A., Parsons, C. M., Jungk, R. A. 2005. The effects of various organic acids on phytate phosphorus utilization in chicks. Poultry Science 84:1356–1362

6) Soltan, M. A. 2008. Effect of dietary organic acid supplementation on egg production, egg quality and some blood serum parameters in laying hens. International Journal of Poultry Sciences 7 (6): 613-621

7) Swiatkiewicz, S., Koreleski, J, Arczewska, A. 2009. Effect of organic acids and prebiotics on bone quality in laying hens fed diets with two levels of calcium and phosphorus. ACTA VET. BRNO 79: 185-193

8) Swiatkiewicz, S., Arczewska, A., Krawczyk, J., Puchala, M., Józefiak, D. 2013. Effects of selected feed additives on the performance of laying hens given a diet rich in maize dried distiller grains with solubles (DDGS). British Poultry Science 54: 478-485

9) Swiatkiewicz, S., Arczewska, A., Krawczyk, J., Puchala, M., Józefiak, D. 2015. Dietary factors improving eggshell quality: an updated review with special emphasis on microelements and feed additives. World's Poultry Science Journal, Vol. 71, March

10) Swiatkiewicz, S., Koreleski, J, Arczewska, A. 2010. Laying performance and eggshell quality in laying hens fed diets supplemented with prebiotics and organic acids. Czech J. Anim. Sci., 55, (7): 294–306

11) Van Immerseel, F., Russell, J. B., Flythe, M. D., Gantois, I., Timbermont, L. Pasmans, F., Haesebrouck, F., Ducatelle, R. 2006. The use of organic acids to combat Salmonella in poultry: a mechanistic explanation of the efficacy. Avian Pathology 35(3), 182-188

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