Dietary fat supplement affected energy and nitrogen metabolism efficiency and shifted rumen fermentation toward glucogenic propionate production via enrichment of Succiniclasticum in male twin lambs

The aim of this study was to investigate the effects of dietary fat on energy and nitrogen (N) metabolism efficiency, rumen fermentation, and microbiota in twin suckling lambs. Thirty pairs of twin male lambs were randomly divided into two groups with one group receiving a high-fat diet (HF) and the other a normal-fat diet (NF). Two diets (milk replacer and starter) of equal protein and different fat levels. The metabolism test was conducted when the lambs were 50–60 days old, and nine pairs of twin lambs were randomly selected for slaughter to collect rumen fluid at 60 days old. The result showed that fat addition increased the final body weight (BW), ruminal ammonia nitrogen (NH₃-N) content, proportion of propionic acid, and estimated methane production (CH_4e) (P<0.05). The high fat diet tended to improve digestive energy (DE), metabolism energy (ME), DE/ME, utilisation of N (0.05<P<0.1). However, microbial crude protein (MCP) content, total volatile fatty acids (VFA), acetic acid ratio, and the ratio of acetate to propionate (A:P) were lower than that in the NF group (P<0.05). Regardless of whether fat is added or not, no different were observed in blood metabolites between the treatment. High-throughput sequencing revealed that fat addition before weaning increased phyla Proteobacteria and genera of Succinivibrio, but decreased the relative abundance of Clostridium IV, Dialister, Roseburia, Acidaminococcus, and Megasphaera genera. These findings indicated that high fat diet improved body weight, energy and nitrogen utilization may by shifting the rumen toward propionate fermentation via the enrichment of Succinivibrio.