This study provides the first comprehensive evaluation of the forage-to-concentrate ratio's effects in a total mixed ratio (TMR) on the dry matter intake (DMI) and ruminal microbiome community changes in Alpine dairy goats. Thirty-two multiparous Alpine dairy goats (53.3 ± 1.14 kg body weight [BW]) were used in this experiment. Treatments were arranged in a completely randomized design with two treatments replicated twice, consisting of a TMR diet that contained either a high-concentrate (HC; 60%:40%) or a low-concentrate (LC; 30:70%) diet. Goats were used in a 45-d experiment to assess the effects of feeding different levels of concentrate diets on DMI, rumen fermentation characteristics, and changes in the ruminal microbiome community. The Calan head gate feeders were used to control individual DMI. The present study showed that BW was similar among the diets (P = 0.126), but DMI was lower (P < 0.05) for the LC diet than for the HC diet. The results showed that the most abundant bacterial species were Clostridium spp. (14.8% and 14.8%), followed by Rikenella spp. (8.2% and 9.7%), Prevotella ruminicola (4.1% and 6.3%), Clostridium sp. (3.5% and 4.8%), and Lachnoclostridium eubacterium contortum (3.4% and 1.2%) in the rumen of dairy goats fed HC and LC diets, respectively. According to the Archaeal 16S rRNA gene sequences, the most abundant Methanogen species were Methanobrevibacter sp. (97.3%), followed by M. wolinii (0.1% and 1.0%), Methanobrevibacter spp. (0.9%), and M. smithii (0.1% and 0.6%) in the rumen of Alpine dairy goats fed HC and LC diets, respectively. Our findings revealed that the rumen of Alpine dairy goats fed HC compared to LC diet had a higher or tended to have higher DMI and proportion of Firmicutes (55.0 vs. 49.2%; P = 0.07), Firmicutes/Bacteroidetes (F/B) ratios (1.9 vs. 1.31; P = 0.06), Chloroflexi (3.7 vs. 1.4%; P < 0.01), Actinobacteria (3.8 vs. 1.5%; P < 0.01), and Tenericutes (1.3 vs. 0.6%; P < 0.01), respectively. Furthermore, the level of Methanobrevibacter sp. was not impacted by diets (P > 0.05). The alpha diversity analysis confirmed that the richness of rumen bacterial species was significantly decreased (P < 0.05) when dairy goats were fed the HC diet compared to the LC diet. The examination of the richness of both Bacteroidetes and Firmicutes, in relation to the relative abundance of microbiota, will help elucidate the structure of gut microbiota as an indicator of animal performance (e.g., milk and meat production).
