Abstract
Low protein diets are commonly used in the growing-finishing pig stage of swine production; however, the effects of low dietary protein on the intestinal microbiota and their metabolites, and their association with pig sex, remain unclear. The present study aimed to assess the impact of a low crude protein (CP) diet on the gut microbiome and metabolome, and to reveal any relationship with sex. Barrows and gilts (both n = 24; initial body = 68.33 ± 0.881 kg) were allocated into two treatments according to sex. The four groups comprised two pairs of gilts and barrows fed with a high protein diet (CP 17% at stage I; CP 13% at stage II) and a low protein diet (CP 15% at stage I; CP 11% at stage II), respectively, for 51 d. Eight pigs in each group were slaughtered and their colon contents were collected. Intestinal microbiota and their metabolites were assessed using 16S rRNA sequencing and tandem mass spectrometry, respectively. The low protein diet increased intestinal microbiota species and richness indices (P < 0.05) in both sexes compared with the high protein diet. The sample Shannon index was different (P < 0.01) between barrows and gilts. At the genus level, unidentified Clostridiales (P < 0.05), Neisseria (P < 0.05), unidentified Prevotellaceae (P < 0.01) and Gracilibacteria (P < 0.05) were affected by dietary protein levels. The relative abundance of unidentified Prevotellaceae was different (P < 0.01) between barrows and gilts. The influence of dietary protein levels on Neisseria (P < 0.05), unidentified Prevotellaceae (P < 0.01) and Gracilibacteria (P < 0.05) were associated with sex. Metabolomic profiling indicated that dietary protein levels mainly affected intestinal metabolites in gilts rather than barrows. A total of 434 differentially abundant metabolites were identified in gilts fed the two protein diets. Correlation analysis identified that six differentially abundant microbiota communities were closely associated with twelve metabolites that were enriched for amino acids, inflammation, immune, and disease-related metabolic pathways. These results suggested that decreasing dietary protein contents changed the intestinal microbiota in growing-finishing pigs, which selectively affected the intestinal metabolite profiles in gilts.
Highlights
In swine production, normal dietary crude protein (CP) concentration is about 15–22%
CP% could be calculated by multiplying the common CP coefficient of 6.25, dietary CP content recommended by NRC (2012) is reckoned decreasing by 2–4% than the previous edition NRC (1998) [National Research Council (NRC), 1998]
Our results demonstrated that the dietary protein content could affect the intestinal microbiota diversity in pigs at the growing-finishing stage, and suggested that the low protein diet formulated in the present study was appropriate and helpful to increase intestinal microbial diversity and species in growingfinishing pigs
Summary
Normal dietary crude protein (CP) concentration is about 15–22%. Reducing dietary protein levels has marked benefits, including increasing nitrogen (N) utilization, lessening seasonally feed costs, especially reducing the excretion of N into the environment. Studies in piglets showed that dietary protein levels altered the intestinal microbiota compositions and microbiallyderived metabolites (Rist et al, 2013). Increasing studies indicate that the compositions and structure of the intestinal microbiota can change dynamically in response to many factors, including feed (Isaacson and Kim, 2012; Ananthakrishnan, 2015). We are interested in whether the impacts of dietary nutrients on intestine microbiota and metabolites are associated with pig sex. This is very important for precision nutrition of sex-specific feeding measures
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