Butyric acid: A nutritional alternative to antibiotics in poultry nutrition

in addition to contributing to the improvement of immunity (Dauksiene et al., 2021).

According to Sengupta et al. (2006), butyric acid has a direct effect on the proliferation, maturation and differentiation of mucosal cells, because it can influence gene expression and protein synthesis, as well influencing the growth and height of villi. Resulting in an increased absorption surface within the small intestine, and optimized nutrient utilization.
   Butyric acid represents one of the most effective feed additives used in animal nutrition as it enhances intestinal health resulting in greater nutrient absorption throughout the gastrointestinal tract. As well as serving as an  energy source for enterocytes. In addition, it contributes to reducing the negative effects caused by stress or diseases which tend to affect animal performance (Imran et al., 2018;  Balta et al., 2021).

Short chain fatty acids, such as butyric acid, are rapidly absorbed and metabolized by mucosal cells. Thus, when birds ingest their diet, absorption and metabolization begin within the crop mucosa and can continue throughout the gastrointestinal tract. This limits the amount of butyric acid that actually reaches the small intestine,  restricting its practical use in animal production (Kaczmarek et al., 2016).

Microencapsulation was developed with the aim of improving protection, bioavailability and controlled release of butyric acid within the animal’s organism. Considering the fact that much of the supplied acid becomes dissociated and absorbed before it even reaches the intestine, impairing its effectiveness along the gastrointestinal tract were pH values tend to be more alkaline.

With the purpose of promoting a slow and continuous release of this acid along the digestive tract, the microencapsulation technique was developed. This method consists of small particles or droplets that are surrounded by a uniform film made up of carbohydrates, cellulose, lipids or proteins. Resulting in small spherical capsules with a uniform wall  (Jyothi Sri et al., 2012).

Sodium butyrate (SB) is a short-chain fatty acid formed after butyric acid is chlorinated by the mineral sodium (Na+2), and its molecular formula is CưH₇OưNa. Since it has greater stability, a less intense odor,as well as having positive effects on performance and intestinal integrity, it is the most commonly used alternative in broiler diets(Jiang et al., 2015; Lan et al).

Considering its multifunctionality and high efficiency, sodium butyrate represents a significant strategy to improve production and health parameters in poultry(Miao et al., 2021).

Kaczmarek et al. (2016) when evaluating the performance of broilers in the period from 1 to 14 days of age, they did not observe differences between diets supplemented with microencapsulated sodium butyrate at doses of 200 mg/kg, 300 mg/kg and 400 mg/kg. Sikandar et al. (2017) found no differences in the performance of broilers at 14 days of age, receiving diets containing 500 mg/kg and 1,000 mg/kg of microencapsulated sodium butyrate. Levy et al. (2015) when analyzing kance of broilers, at 21 days, fed 0, 100, 200, 300, 400 and 500 mg/kg of encapsulated butyric acid, observed lower diet intake with the highest acid dosage and worsening of feed conversion. Likewise, Imran et al. (2018) when testing different doses (250, 350 and 450 mg/kg) of microencapsulated butyric acid in the diet of broilers indicated a decrease in the consumption of broilers when they received diets with the highest amount of acid. Wu et al. (2018) there was no difference in the performance of broilers at 21 days of age, fed different doses of sodium butyrate (200, 400, 800 and 1,000 mg/kg) and antibiotic. Lan et al. (2020) when evaluating the effects of BS in broilers, they noticed an improvement in performance, in which birds linearly increased the average daily weight gain. BS supplementation increased the relative  length of the duodenum, jejunum, and ileus, as well as improved intestinal structure, increasing villi height in the jejunum and ileum, in addition to the caliciform cell count in the duodenum, jejunum and ileum.

Wang et al. (2021) in his research with butyric acid found that body Sikandar et al. (2017)weight increased at the beginning of the rearing phase (7 and 14 days) compared to birds that did not receive any type of additive. In addition, there was an increase in the height of duodenal  villi at 20 and 33 days of age. The increase in villi height was predictable, as enterocytes use butyric acid as an energy source, resulting in the development of villi. Butyric acid induces gene expression and protein production, making the intestinal epithelial barrier less permeable to pathogens and toxins, which can contribute to the development and maturity of intestinal health. Boling et al. (2000), Abdel-Fattah et al. (2008) and Kana et al. (2011) reported that higher levels of acids incorporated into the diet decreased feed intake by birds, which may be due to the palatability of acidified diets during the first days. However, in the subsequent stages of rearing, birds tend to adapt to the acidification of diets.

Several results have been reported, and the differences in the responses found may be due to the available content of sodium butyrate, animal age, immune status and hygiene of the environment. Microencapsulated sodium butyrate can be used as an alternative to the chemical antimicrobial, however, it is important to consider the dosage to be used in animal diets, since many studies have not defined a correct dose.