Recent advances of using organic acids and essential oils as in-feed antibiotic alternative in poultry feeds

Antibiotics used in animal feeds have recently been strictly regulated to avoid antibiotic resistance in humans. Thus, scientists are compelled to find new feed additives to replace antibiotics in feed. Apart from having a zero effect on human health, new alternatives may even be able to further improve production performance. Essential oils (EOs) and organic acids (OAs) stood out as powerful and useful replacements for both animal production and human population. These are added to chicken diets and drinking water to induce a favourable growth response. Hence, enhancing the nutrient digestibility, performance, and immunity of birds, OAs and EOs are used in livestock production mainly to inhibit the growth of harmful bacteria and simultaneously maintain the balance of intestinal bacteria. This improves the digestion of nutrients and mineral absorption which will eventually lead to better feed efficiency. The addition of OAs and EOs also causes the intestinal lining to thin, which further enhances nutrient absorption and utilization. Not only for poultry production, the effect of OAs and EOs can also improve poultry immunity and antioxidant capacity. However, the effects will vary depending on the type of OAs and EOs because their mode of action is dependent on their pKa value. In the present review, beneficial properties of OAs and EOs, as well as various dose combinations, to promote their optimal use in poultry nutrition and production will be examined. Their effects on supporting protein digestion, faster absorption of minerals, especially microminerals, stimulating growth performance, regulating antioxidant capacity, and improving immune response will be explored.