# Effects of Lipopolysaccharide Challenge on Growth Performance and Immune Function of Yellow-Feathered Broilers

## TL;DR

Repeated LPS injections in yellow-feathered broilers reduce growth and immune function, causing inflammation and organ atrophy.

## Contribution

The study shows that three LPS injections are sufficient to induce immune stress and damage in broilers.

## Key findings

- Three LPS injections significantly reduce growth performance and immune organ indices in broilers.
- LPS increases inflammatory cytokines (IL-1β, IL-6, IFN-γ) and activates the TLR4/MyD88 pathway.
- Immune stress is established after three LPS challenges, with lasting effects on feed intake and weight gain.

## Abstract

This study investigated the effects of repeated lipopolysaccharide (LPS) injections on growth performance and immune function of yellow-feathered broilers. Broilers injected with LPS (1 mg/kg body weight) on days 21, 23, 25, and 27 exhibited progressively more severe effects: growth performance declined significantly after the second and third injections, and key immune organs atrophied. LPS consistently induced a strong inflammatory response, increasing the levels of IL-1β, IL-6, and IFN-γ in the liver and jejunal mucosa, and upregulating the TLR4/MyD88 immune pathway genes after the third injection. These findings demonstrate that three LPS injections are sufficient to induce significant immune damage and establish an immune stress model in the broilers.

This study aimed to investigate the effect of lipopolysaccharide challenge on growth performance and immune function in yellow-feathered broilers. A total of 140 yellow-feathered broilers (1-day-old) were randomly assigned to two treatments (control group and LPS group) with seven replicates of 10 chicks each. Broilers in the LPS group were injected intraperitoneally with LPS (1 mg/kg body weight) on days 21, 23, 25, and 27, while broilers in the control group were injected intraperitoneally at an equivalent volume of sterile saline on the corresponding days. After 24 h of each injection, one chicken from each replicate was randomly selected for slaughter and sampling. The results indicate that the first LPS challenge significantly elevated jejunal mucosal IL-6 levels compared with the control group (p < 0.05). After the second injection, average daily feed intake (ADFI), average daily weight gain (ADG), and body weight gain (BWG) of broilers were decreased in the LPS group compared to the control group (p < 0.05). Additionally, IL-1β levels were increased in the liver and jejunal mucosa of broilers in the LPS group (p < 0.05). After the third injection, the ADFI, ADG, BWG and feed conversion ratio (FCR) were reduced in the LPS group compared to the control group. LPS also caused a decrease in the broiler thymus index and bursa index. In addition, the levels of IL-1β, IL-6 and IFN-γ in the jejunal mucosa of broilers in the LPS group were higher than those in the control group (p < 0.05). The levels of IL-1β and IFN-γ in the liver of the LPS group were significantly higher than those of the control group (p < 0.05). The mRNA expression of IL-1β, IL-6, and IFN-γ in the jejunum and liver of the LPS group was significantly higher than that of the control group (p < 0.05). Furthermore, the mRNA expression of TLR4 and MyD88 in both the liver and jejunal mucosa of broilers in the LPS group was significantly higher than that in the control group (p < 0.05). Following the fourth LPS injection, the ADFI, ADG, BWG, and spleen index of LPS group decreased significantly compared to the control group. Concurrently, a significant increase in the content of IFN-γ in the liver was observed. In conclusion, three times of LPS stimulation can cause significant immune damage and induce an immune stress model.