Effect of Caragana korshinskii Kom. as a partial substitution for sheep forage on intake, digestibility, growth, carcass features, and the rumen bacterial community

Abstract

The aim of this study was to verify that Caragana korshinskii Kom. (CK) as a component of sheep forage influences lamb digestibility and rumen fermentation by altering the rumen microbial community. Hence, 12 female Tan sheep were allocated into 2 groups: receiving (CK group) or not (control group) 10% of the diet forage fraction with CK. During the 60-day experiment, growth performance, apparent digestibility, rumen volatile fatty acids (VFAs), and nitrogen balance were measured. Meanwhile, the rumen bacterial community diversity and composition were detected by the 16S rRNA sequence. The results indicated that the apparent digestibility of acid detergent fibre (ADF) tended to be higher (0.05 < P < 0.10), and the feed conversion efficiency was improved (P < 0.05) when CK was offered. Compared to those under alfalfa, the composition and abundance of the rumen microbial community were altered in the CK group, and the phylum Firmicutes, which is involved in promoting fibre digestion, increased in abundance. Moreover, VFAs tended to decrease (0.05 < P < 0.10), and the molar proportion of butyrate declined; similarly, levels of hypoxanthine and xanthine were lower (P < 0.05) in the sheep fed CK and may have been responsible for the decreased abundance of Fibrobacter spp., which are cellulolytic ruminal bacteria associated with VFA production.

Keywords: Caragana; Nitrogen utilisation; Rumen microbiota; Tan sheep; Volatile fatty acids.

Fig. 1

Main rumen bacteria of Tan sheep offered diets with or without Caragana korshinskii Kom. a Bacterial alpha diversity based on Shannon diversity and Chao 1 indexes. b PCoA plot based on the Bray–Curtis dissimilarity of the microbiota. Each dot represents the composition of the microbiota of each sample. Samples were grouped by colour as the labels show. Control: diets without Caragana korshinskii Kom., n = 6; CK: diets with Caragana korshinskii Kom., n = 6

Fig. 2

Comparisons of the rumen bacteria relative abundance in Tan sheep offered diets with or without Caragana korshinskii Kom. at different classification levels. a Bacterial taxonomic composition at the phylum level. The phyla Bacteroidetes and Firmicutes dominated the core microbiome in Tan sheep, followed by the phylum Proteobacteria. b A heatmap was generated from hierarchical clustering analysis of the normalised relative abundances of the top 50 genera in the 2 Tan sheep groups. Genera with square brackets are proposed by the Greengenes curators and indicate the recommended taxonomy. c Rumen bacteria with LDA scores greater than 2 were speculated to have different abundances between control and CK groups. d The cladogram displays the evolutionary relationship at three levels of the taxonomy (class, order, family) for taxa with scores over 2. Control: diets without Caragana korshinskii Kom., n = 6; CK: diets with Caragana korshinskii Kom., n = 6