The effect of sex and dietary crude protein level on nutrient transporter gene expression and cecal microbiota populations in broiler chickens

Abstract

<p>It is well known that male and female broilers differ in their growth performance and that many physiological factors contribute to this difference. The aim of this experiment is to investigate if there are differences between males and female broilers in cecal microbiota and nutrient transporter gene expression and if these differences play a role in the growth performance of broilers. The possible effect of protein level and its interaction with sex on microbiota and expression of the nutrient transporters were also investigated. Samples were collected from male and female birds fed either standard crude protein (SCP) or reduced crude protein diets (RCP) at the age of d 35. The experiment was designed as a 2 × 2 factorial arrangement of treatments consisting of 448 Cobb 500 broilers assigned to 32 floor pens with 4 treatments, 8 replicates, and 14 birds per pen for performance measurements. The factors were sex (male or female) and dietary crude protein (CP) level (standard or reduced). Body weight gain (BWG), feed intake and feed conversion ratio were recorded for each pen. Sex had a significant effect on BWG and FCR (P < 0.001) where males had a significantly higher BWG and better FCR compared to females. There was a significant interaction between sex and protein level on feed intake (FI) (P < 0.05), where male birds had a higher FI compared to female birds only when the birds were fed SCP but not RCP diets. There was a significant interaction between CP level and sex on the expression of <i>CAT2</i> (<i>P</i> = 0.02) and <i>PEPT2</i> (<i>P</i> = 0.026) where the genes were significantly upregulated in females but only when the RCP diet was fed. The RCP diet upregulated the expression of <i>B^oAT</i> (<i>P</i> = 0.03) as a main effect. Female birds had significantly higher expression of the <i>PepT-2</i> gene compared to the males. The alpha diversity of cecal microbiota showed differences among the treatments. The Shannon diversity index was statistically higher (P = 0.036) for males fed the SCP diet and the Chao1 index for evenness was statistically higher (P = 0.027) in females fed the SCP diet. There was also a difference in the relative abundance of the 15 most common genera found in the cecal content of the broilers in this experiment and lastly, the differential composition of microbiota between the different treatments was also significantly different.</p><p>This study suggests that chickens are able to compensate for a reduction in AA substrates when fed a low CP diet through the upregulation of certain AA transporters, females may adapt to low CP diets better by such upregulation compared to males, and lastly, sex has an effect on the cecal microbial population and these differences contribute towards the performance differences between male and female broilers.</p>