Organic acid salts are often included as feed additives in livestock nutrition as feed preservatives but also as growth promoters, intestinal microbiota enhancers, and feed intake regulator. Yet, these beneficial effects on poultry performance and health are dose dependent and can lead to detrimental effects at elevated concentrations.
What are the benefits of adding organic acids into feed?
Due to their chemical properties, dietary organic acids act as growth promoters and feed preservatives in poultry diets. Indeed, organic acids can suppress bacteria development at varying concentrations depending on the acid of interest and its chemical properties (stronger acids required lower concentration to achieve the same effect). For example, the minimal concentrations to inhibit bacteria growth ranges from 0.1% formic acid to 0.4% lactic acid for Salmonella typhimurium, Escherichia coli, Campylobacter jejuni, Staphylococcus aureus, and Clostridium spp. Certainly, organic acids have shown great efficacy against these economically relevant bacteria and fungi responsible for feed spoilage and food-borne diseases. Their antimicrobial efficiency relies on their capacity to enter inside the bacteria cell wall and lower their pH leading to cellular death. Depending on their pH sensitivity, some bacteria species are more resistant to organic acid exposure and may require greater concentration or stronger acids (e.g., lactic or formic acids compared to propionic acid) to kill them. As acids are corrosive in their liquid form, dietary organic acids are often added into feed as salts (e.g., calcium propionate, calcium lactate, calcium butyrate) to prevent acidosis and also for easy, safe management.
Beside lowering the risk of pathogen infection, proper inclusion rate of organic acids can support body weight gain and enhance feed conversion ratio. For example, inclusion rate around 0.25-0.50% of calcium propionate in poultry diets have been shown to have antimicrobial properties but also improve feed efficiency. In poultry diets, organic acids are associated with higher digestibility as well as nutrient absorption and utilization at different levels. Salts of organic acids can buffer the intestinal pH during digestion resulting in improving protein digestibility. Also, the stimulatory effect of organic acid salt on the morphology of the small intestine has been described in previous studies. Data from these studies highlight that, at optimal concentrations like above-mentioned, organic acids can promote integrity of the small intestines instead of resulting in gastrointestinal damage. Upon digestion, organic acids can further advance nutrient utilization as intermediates of metabolic pathways. Overall, and regardless of the mode of action, field research reinforces that enhanced digestibility and improved nutrient absorption and utilization translate into faster growth rate and/or heavy carcass weight when organic acid salts are used warily as feed additives. Similarly, feed efficiency also increased in poultry diets when organic acid salts are added jointly other feed additives such as dietary fibre. These effects altogether support the positive effect of organic acid salts from optimal poultry performance and health to food safety mediating multiple steps along the way in both broiler and layer chickens.
What about the side effects of dietary organic acids?
Early signs of negative side effects of organic acids are subtle and depend on poultry age, previous experience with organic acids, and organic acid of choice. Regardless of metabolic acidosis, rising intake of organic acids can result in lower feed intake, hyperactivity and restlessness, and onset of health issues and other welfare problems (particularly in naïve chickens). Exposure and inclusion of organic acids should therefore be gradual in grower diets so chicks can adjust to small concentrations until reaching a beneficial concentration for growth promotion, pathogen bacteria control, and feed preservative. Although chickens can build up tolerance to organic acids, concentrations above 1% can reduce palatability of poultry diets and induce a negative sensation after feeding. Altogether, broilers fed with diets at an inclusion rate of 1-3% organic acid salt, and beyond, show a linear decrease in feed intake. Research suggests that chickens fed grower diets with organic acids at a higher concentration than before ate less feed and showed avoidance for that diet. Consequently, despite potential benefits in digestibility and nutrient utilization, poultry performance is compromised when inclusion rate exceeds 1.5% due to low daily feed intake.
Gauging what chickens experience when fed diets with 5% organic acid inclusion is not straightforward, but behavioural response of chickens suggest discomfort and undergoing stress under these conditions. In addition to these welfare concerns, greater concentrations of organic acids as feed additive induce health problems in the gastrointestinal tract. For example, results from research using experimental diets at 6-9% calcium propionate, fed unrestricted, indicated that birds started to develop lesions in their crops and stomachs. Low levels of organic acid salt appear to have a minimal effect on intestinal pH, but higher levels can underlie acidosis. Therefore, including organic acid salts as feed additives in grower and adult diets are advantageous to prompt body weight gain and lower count of pathogen bacteria and fungi in feed, but its inclusion rate should be carefully examined to prevent voluntary feed intake drop and other possible welfare or health problems.
