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Novel and innovative approaches are needed to maintain poultry production efficiency in the absence of antibiotics, and their development requires a fundamental understanding of how intestinal physiology relates to feed nutrient use. We have identified physiological and microbial signatures within commercial broilers that are associated with metabolic efficiency. Expression patterns of nutrient transporters and cytokines suggest that the bird’s ability to digest and absorb dietary amino acids and glucose may be linked to inflammatory status of the intestine. Intestinal microbial populations associated with high metabolic efficiency represent targets for novel strategies to maintain production in the absence of antibiotics through the use of feed additives that promote an intestinal ecology associated with improved feed nutrient utilization.


Antibiotics have historically been used by the broiler industry to enhance production by improving growth and feed efficiency while reducing morbidity and mortality due to subclinical disease. Implementation of the Veterinary Feed Directive has meant that medically important antibiotics can no longer be used for production purposes in animal agriculture. Furthermore, increased consumer demand for food produced without antibiotics has led the poultry industry to move towards antibiotic-free production, with an estimated 50% of broiler flocks raised in a “no antibiotics ever” program. With these regulatory and societal pressures in place, there is a need for strategies that maintain production efficiency and improve flock uniformity in the absence of antibiotics.


Due to the pressing need for development of strategies that maintain production efficiency in the absence of antibiotics and the high cost of feed in broiler production systems, effective strategies must maintain high levels of feed nutrient use. Therefore, it is imperative that a holistic understanding of factors regulating feed efficiency be developed. From a single population of male commercial broilers, we individually determined feed intake, body weight gain, and feed conversion ratio (FCR; g feed intake/g body weight gain) between post-hatch days 7 and 35. From this data, the six best (FCR = 1.41) and worst (FCR=1.69) efficiency birds that differed significantly in FCR but not feed intake or body weight gain were identified, and intestinal tissue was collected. Jejunum and cecal tonsil were analyzed for expression levels of nutrient transporters and inflammatory cytokines, jejunum and ileum mucosa were analyzed for amino acid and organic acid levels, and microbial composition and metabolic activity were determined in all intestinal sections. Jejunal expression of two glucose transporters was elevated in birds with poor efficiency, and an amino acid transporter for two essential amino acids, lysine and arginine, was increased in jejunum of birds with improved efficiency. These birds also exhibited higher levels of the transporter for glutamate, an amino acid that can serve as a neurotransmitter, suggesting differences in gut-brain axis activity might contribute to metabolic efficiency. Increased expression of pro-inflammatory cytokines in cecal tonsil of birds with lower metabolic efficiency was also observed. Mucosal alanine, glutamate, serine, and threonine were higher in low efficiency jejunum and ileum. Lactate and succinate were also consistently higher in both mucosal sections of birds with reduced metabolic efficiency; citrate was higher in mucosa of high efficiency jejunum and ileum. Of note, 1-methylhistidine was detected only in mucosa of birds with low efficiency, suggesting it may serve as a biomarker for dysbiosis associated with poor metabolic efficiency. Genotypic microbiome analysis revealed differences in taxa between birds with different metabolic efficiencies in all sections, including those within the Firmicutes and Bacteriodetes phyla. Phenotypic microbiome analysis with single C-source arrays indicated that microbial respiration was higher in low efficiency birds in duodenal, jejunal, and cecal segments, with metabolism of glycogen, alpha-D-lactose, glucose-1-phosphate, and gamma-hydroxyl-butyric acid differing between groups.


We have shown that intestinal physiology plays a critical role in influencing efficiency of feed nutrient use in broiler chickens through altering the bird’s ability to digest and absorb dietary glucose and amino acids, which is likely influenced by inflammatory status of the intestinal tissue. Birds exhibiting reduced metabolic efficiency could also have increased endogenous amino acid losses in addition to reduced absorptive capacity. Microbial ecological signatures associated with differing metabolic efficiencies were identified, and these represent targets for novel strategies to maintain or improve production efficiency of broilers without the use of antibiotics. Current efforts are aimed at investigating novel approaches for improvement of production efficiency that include identification of the mechanism of action of dietary additives, including antibiotics, that appear to enhance feed efficiency through influencing intestinal physiology and microbial ecology. Successful development and implementation of strategies that improve FCR by even a few points would substantially improve profit margins for broiler producers, because feed accounts for over 70% of their production cost. As increases in feed conversion are likely reflective of shifts in nutrient partitioning that favor muscle accretion over fat deposition, such strategies would further increase production efficiency by enhancing meat production.

State Issue

Animal Production


  • Year: 2020
  • Geographic Scope: National
  • County: Clarke
  • Location: College Station, Athens
  • Program Areas:
    • Agriculture & Natural Resources


  • Ellestad, Laura


CAES Collaborator(s)

  • Rothrock, Michael

Non-CAES Collaborator(s)

  • Guard, Jean
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