Dietary NDF/Starch Ratio Modulates Colonic Microbiota and Metabolites in Lambs before and after Weaning

Abstract

The neutral detergent fiber (NDF)/starch ratio is a key determinant of the carbohydrate composition in ruminant diets, which affects the development of the gastrointestinal tract and animal growth. In this study, we used a combination of 16S amplicon sequencing and metabolomics technologies to reveal changes in the microbiota and their metabolites associated with digestive matter in the colon of lambs between different starter NDF/starch ratios and before and after weaning. A total of 40 male lambs of Hu sheep with a newborn weight of 3.14 ± 0.05 kg were selected for the experiment and fed with breast milk until 10 days of age, and were randomly divided into 2 groups, which were fed ad libitum with a starter of NDF/starch of 0.5 (A) or 1.0 (B) for a period of 56 days, and then weaned off the milk powder at 35 days of age. Six lambs with weights close to the average weight of the group were selected for slaughter in each of the two groups before (35 days of age) and after weaning (56 days of age), and were accordingly named A35, A56, B35 and B56. The results showed that, before weaning, the concentrations of acetic acid, propionic acid, butyric acid and total volatile fatty acids (TVFA) in group B35 were significantly higher than those in group A35 (p < 0.05), while the concentrations of isobutyric acid, valeric acid and isovaleric acid were significantly lower than those in group A35 (p < 0.05). After weaning, the concentrations of all volatile acids and total acids in group B56 were significantly lower than those in group A56 (p < 0.01). At the phylum level, the dominant phyla identified were Firmicutes and Bacteroidetes; the relative abundances of Firmicutes and Desulfobacterota were significantly higher and lower in group B35 than in group A35, respectively (p < 0.05); the relative abundances of Euryarchaeota and Desulfobacterota were significantly higher and lower in group A56 than in group A35 (p < 0.05); and, at the genus level, the relative abundance of Lachnospiraceae_FCS020_group and Eubacterium nodatum group had higher relative abundance in group B35 before weaning (p < 0.05). Metabolomic results showed that feeding 1.0 NDF/starch ratio starter before weaning significantly up-regulated (p < 0.05) the concentrations of several anti-inflammatory-related metabolites such as lithocholic acid, oleanolic acid and LysoP. After weaning, the number of differential microorganisms and anti-inflammatory-related metabolites decreased between the two ratios. In summary, feeding a 1.0 NDF/starch ratio starter may be more effective in regulating microbial fermentation, leading to an increase in beneficial microbiota and metabolites, thus improving colonic environmental homeostasis in lambs before and after weaning.