The Interactive Effects of Nutrient Density and Breed on Growth Performance and Gut Microbiota in Broilers

This study investigated whether variations in growth response to low nutrient density across breeds are linked to microbiota regulation. Arbor Acres (<b>AA</b>) and Beijing-You (<b>BY</b>) were fed high- (<b>HN</b>) and low-nutrient (<b>LN</b>) diets from day (<b>d</b>) 0 to d42. Body weight, feed intake, and intestinal measurements were recorded, and microbiota from the ileum and cecum were analyzed on d7, d21, and d42. Results showed that AA broilers had greater growth performance with a lower feed conversion ratio (<b>FCR</b>) and greater average daily gain (<b>ADG</b>) than BY chickens. The LN diet negatively affected AA broiler growth due to impaired intestinal development, while BY chickens compensated by increasing feed intake. Microbiota composition was primarily affected by breed than by nutrient density, with AA broilers having more beneficial bacteria and BY chickens having more short-chain fatty acid (<b>SCFA</b>)-producing bacteria. The LN diets reduced anti-inflammatory bacteria such as <i>Shuttleworthia</i> and <i>Eisenbergiella</i> in the cecum on d7. By d21, LN diets decreased <i>Lactobacillus</i> and increased proinflammatory <i>Marvinbryantia</i>, potentially impairing growth. However, LN diets enriched SCFA-producing bacteria like <i>Ruminococcaceae_UCG.013</i>, <i>Eisenbergiella</i>, and <i>Tyzzerella</i> in BY chickens and <i>Faecalitalea</i> in AA broilers by d21, which may benefit gut health. By d42, LN diets reduced genera linked to intestinal permeability and fat deposition, including <i>Ruminococcus_torques_group</i>, <i>Romboutsia</i>, <i>Erysipelatoclostridium</i>, and <i>Oscillibacter</i>. Additionally, LN diets enriched <i>Christensenellaceae_R-7_group</i> in AA broilers, associated with intestinal barrier integrity, and increased anti-inflammatory bacteria <i>Alistipes</i> and <i>Barnesiella</i> in AA broilers and BY chickens, respectively, by d42. Overall, AA broilers were more susceptible to reduced nutrient density due to impaired intestinal development, while BY chickens adapted better by increasing feed intake. The microbiota responses to low nutrient density varied over time, potentially negatively affecting gut health in the early stage and growth in the middle stage but possibly improving lipid deposition and gut health in the middle and late stages.