Effects of different dietary forage sources on the structure and function of cecum bacteria in Hu lambs

The purpose of this experiment was to investigate the effect of forage sources on the structure and function of cecum bacteria in Hu lambs. Sixty seven-day-old (3.77 ± 0.46) kg Hu lambs were divided into four groups of 15 lambs in each group. The forage sources were alfalfa (Medicago sativa) hay (AH) and oat (Avena sativa) hay (OH), whereas the non-forage sources were beet pulp (Beta vulgaris) (BP) and soybean hulls (Glycine max) (SH). The lambs were allowed to freely feed and drink throughout the entire process. At the age of 70 days, six lambs were randomly selected from each of the treatment group and slaughtered. Twenty-four samples of cecum contents were collected for 16S rDNA sequencing. The results showed that 72482 sequence data and 2999 operational taxonomic units (OTUs) were obtained from 24 cecal content samples, and 12 phyla, 54 classes, 103 orders, 174 families, and 349 genera were obtained from species annotations. The observed species index, Simpson index, and Shannon index in OH group were significantly higher than those in AH group (P < 0.05). Firmicutes and Bacteroidetes were the most abundant phyla in the cecum, and Rumenococcus was the dominant family. Trichospiraceae in OH group was significantly higher than that in AH and SH groups, and Christensenaceae in OH group was significantly higher than that in AH and BP groups (P < 0.05). Proteobacteria in BP group was significantly higher than that in AH, SH, and OH groups (P < 0.05), and Spirochaetes in BP group was significantly higher than that in AH and SH groups (P < 0.01). Anaerostipes were significantly higher in the OH group than in the AH group (P < 0.05), and unidentified Erysipelotrichaceae spp. were significantly higher in the SH and OH groups than in the AH and BP groups (P < 0.05). Functional prediction analysis using the Tax4Fun method revealed that carbohydrate, lipid, energy, and amino acid metabolisms were the predominant metabolisms in the cecum microbiota of lake lambs. Correlation analysis showed a positive correlation between Muribaculaceae and live weight and daily weight gain (P < 0.05), and a negative correlation between Prevotellaceae and live weight and daily weight gain (P < 0.05). In summary, this study shows that different forage sources in starter diets have significant structural and functional effects on the cecum bacteria in lake lambs owing to their different fiber structure.