Gut Microbiome Influences Poultry Welfare

In this issue:

• Introduction to the gut microbiome
• The function of prominent bacterial phyla
• Introduction to the gut-brain axis
• How microbial imbalance affects poultry welfare
• Practical strategies to improve the gut health of poultry

What is the gut microbiome?

• A microbial community, their collective genetic material and metabolites, within the digestive tract of an animal that usually has a symbiotic relationship with the host (Broom and Kogut, 2018)

Why is gut microbiota important?

• Imbalance of the gut microbiota can affect disease resistance, heighten stress and fear responses, and contribute to problematic behaviors such as feather pecking and cannibalism

What makes up the chicken gut microbiota?

• The four most abundant bacterial phyla in the chicken gut are - Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria (Oakley et al., 2014)
• Beyond bacteria, the gut microbiota also consist of viruses, archaea, fungi, and protozoa. This article will focus on gut bacteria as they are the most abundant microbiota in the gut.

Major functions of gut microbiota

• Breakdown of food products (lipids, proteins, and sugars)
• Direct and indirect interaction with host cells to modulate mucosal immune function, enteric nervous system, enterochromaffin cell function (neurotransmitter production)

Firmicutes

• Gram-positive*
• Aerobic and anaerobic
• Carbohydrates ⟶ short-chain fatty acids (SCFA) like butyrate

Proteobacteria

• Gram-negative^
• Aerobic and anaerobic
• Carbohydrates, amino acids, lipids ⟶ SCFA, protein, energy
• Some are opportunistic pathogens (E. coli and Salmonella)

Bacteriodetes

• Gram-negative
• Mostly anaerobic
• Complex carbohydrates ⟶ SCFA (acetate, propionate)

Actinobacteria

• Gram-positive
• Aerobic and anaerobic
• Carbohydrates, amino acids, lipids ⟶ energy and protein
• Important for gut homeostasis

The gut-brain axis

• The gut-brain axis is a communication network linking the digestive system and the brain through the nervous, immune, and endocrine systems
• Gut microbiota can influence behavior, stress responses, and overall health by producing neurotransmitters and metabolites
• Understanding this connection can help improve poultry welfare, reduce stress, and enhance productivity through precision feeding of probiotics

Microbiota imbalance and welfare

• Microbiota imbalance is a reduction in beneficial bacteria and increase harmful bacteria such as E. coli, Campylobater, and Salmonella (Kogut, 2019)
• Associated with stress and fear responses
• Chronic heat stress decreases the abundance of beneficial bacterial families like Lactobacillus and Bifidobacterium (Lyte et al., 2025)
• Chickens with longer tonic immobility show decreased microbial diversity and fewer beneficial gut bacteria (Gao et al., 2025). For more information on tonic immobility see Poultry Press Vol. 33: Fear Tests in Poultry Microbiota imbalance and welfare
• Increases feather pecking and cannibalism risk - high feather pecking birds show altered gut metabolite production (Meyer et al., 2013) and microbiome composition (Birkl et al., 2018). For more information on injurious pecking see Poultry Press Vol. 7: Injurious Pecking Behavior
• There is an association between reduced microbiome diversity and lower cumulative Welfare Quality® scores on commercial broiler farms (Di Marcantonio et al., 2022). This was based on four metrics: good health, good feeding, good housing, and appropriate behavior. High abundance of pathogenic microbiota was also found in lower scoring farms.

Practical strategies to improve gut health

Other strategies to increase microbiota diversity include:

• Reducing stocking density (Guardia et al., 2011). For more information on stocking density and welfare see Poultry Press Vol. 39: Stocking density and broiler behavior
• Ensuring good ventilation to minimize thermal stress (Lyte et al., 2025)
• Providing environmental enrichment, e.g. dark brooder (de Jong et al., 2022) or increased environmental complexity (Hubert et al., 2019) can reduce stress response subsequent risk to microbiota diversity. For more information on environmental enrichments see Poultry Press Vol 5: Effective Enrichment Strategies for Broilers and Poultry Press Vol. 57: Effect Enrichments for Broiler Breeders