Bacitracin supplementation as a growth promoter down-regulates innate and adaptive cytokines in broilers intestine

Authors: DALPONT, GABRIELA - Texas A&M University; LEE, ANNAH - Texas A&M University; BORTOLUZZI, CRISTIANO - Dsm; FARNELL, YUHUA - Texas A&M University; GOUGOULIAS, CHRISTOS - Innovad Nv/sa; Kogut, Michael - Mike

Submitted to: Poultry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2023
Publication Date: 8/29/2023
Citation: Dalpont, G.C., Lee, A., Bortoluzzi, C., Farnell, Y.Z., Gougoulias, C., Kogut, M.H. 2023. Bacitracin supplementation as a growth promoter down-regulates innate and adaptive cytokines in broilers intestine. Poultry. 2:411-417. https://doi.org/10.3390/poultry2030030.
DOI: https://doi.org/10.3390/poultry2030030

Interpretive Summary: For decades, poultry farmers have fed low levels of AGPs (antibiotic growth promoters) to chickens because they seemed to cause increased growth in a shorter time period. Although no one understood exactly why antibiotics provided this effect, it was not because the antibiotics killed germs since the doses given to the chicks were much less than required for significant antimicrobial activity. However, consumer and regulatory pressures have demanded, in recent years, the removal of the antibiotics from animal feed to prevent acquisition of antibiotic resistance in germs that infect humans. Therefore, there has been a great demand for the development of alternatives to antibiotics that provide growth promoting aspects without incurring drug resistance. One of the great stumbling blocks to identifying new alternatives to antibiotics was the lack of knowledge of how they increased the growth of the chicks. This study was conducted to try to identify whether AGPs decreased the immune response in the guts of chicks allowing the birds to use more energy for growth instead of constantly stimulating a local immune response. For the first time, we have identified a potential mechanism of the growth promoting abilities of AGPs, suppressing immune function in the gut. Now that we understand how AGPs work, new alternatives can be developed that use these same mechanisms without harming the ability of the chicks to fight infections. These results are important to the poultry industry because replacements for AGPs are needed to enhance production effiency.

Technical Abstract: In the past decade, the withdrawal of antibiotics as growth promoters (AGPs) has increased some poultry industry challenges, such as the rise of intestinal diseases. Experts advocate that AGPs improved performance due to modulation of the intestinal microbiota with resulting anti-inflammatory effects. However, we still do not fully comprehend the impact and interactions of AGPs with the host intestinal immune system, which affects the development of effective alternatives for AGPs. Therefore, in this study, we aimed to expand the knowledge about how bacitracin used as AGP impacted the intestinal immune system. Ninety day-of-hatch chickens were randomly assigned to two treatments groups with three repetitions of 15 birds, a Control (CNT) group with a corn/soybean meal standard diet, and a control diet supplemented with 50g/ton of feed of Bacitracin (BMD). The cytokines and chemokines production (IFN-alpha, IFN-gamma, IL-16, IL-10, IL-21, IL-6, M-CSF, MIP-3alpha, MIP-1beta, VEGF and CCL-5) were assessed in the jejunum and ileum at 14, 21, 28, and 36 days of age by using chicken-specific cytokine/chemokine peptide ELISA array. Broilers with BMD supplementation were found to have a lower production of IL-16, IFN-gamma, M-CSF, IL-21, MIP-1beta, and VEGF in the jejunum at 14d. However, from 21 through 36 days, the affect of BMD on cytokine production in the jejunum was negligible with the exception of CCL-5 which was reduced at D36. In the ileum, BMD effects on the cytokine profile started at 28d, when BMD-supplemented broilers showed a reduced IL-6 production level. At day 36, BMD reduced IL-16 and MIP-3alpha production, but increased VEGF concentration in the ileum tissue. The present study demonstrated that the use of bacitracin as AGP modulates the small intestine immune system, especially in the first phase of the broiler's life (up to 14 days). Moreover, BMD anti-inflammatory effects include not only innate immunity but also affected the development of the adaptive immune response as seen by the decreased production of IL-21 and IL-16. These results demonstrate that a commonly used AGP in broiler feed had a local anti-inflammatory effect.