Effects of Different Levels of Lycium ruthenicum Leaves on Rumen Fermentation, Amino Acids, Fatty Acids and Rumen Bacterial Diversity in Sheep

<i>Lycium ruthenicum</i> leaves (LRL), as an agricultural by-product rich in bioactive compounds, can be used as an unconventional feedstuff in animal diets and have the potential to improve animal health. This study investigates the effects of dietary supplementation with graded levels of LRL on rumen fermentation, meat amino acid and fatty acid profiles, and rumen bacterial diversity in sheep. Forty three-month-old male Dorper × Hu crossbred F1 lambs with an initial body weight of 29.58 ± 2.06 kg were randomly assigned to four groups (<i>n</i> = 10). Over a continuous 63-day trial period, the lambs were fed diets containing 0%, 5%, 10%, and 15% LRL, respectively. At the end of the trial, rumen fluid and longissimus dorsi muscle samples were collected to assess rumen fermentation characteristics, bacterial community structure, and meat quality. The results showed that: (1) The concentrations of acetate, butyrate, and total volatile fatty acids (TVFA) in the rumen were increased in the LRL5% group (<i>p</i> < 0.05 or <i>p</i> < 0.01). (2) The relative abundance of the phylum Firmicutes and the genus <i>Ruminococcus</i> increased (<i>p</i> < 0.05), while the relative abundance of the genus <i>Prevotella</i> decreased (<i>p</i> < 0.05) in the LRL5% group. (3) Meat L* increased (<i>p</i> < 0.05), and a* decreased (<i>p</i> < 0.05) in the LRL-supplemented groups. (4) The content of sweet amino acids in meat increased in LRL groups (<i>p</i> < 0.05). Moreover, the contents of non-essential amino acids, sweet amino acids, and total amino acids in meat increased linearly with increasing dietary LRL levels (<i>p</i> < 0.05). (5) Compared with the CON group, the content of C18:0 in meat decreased in the LRL5% group (<i>p</i> < 0.05), while the content of C20:1 increased in the LRL10% group (<i>p</i> < 0.05). In conclusion, dietary supplementation with LRL can improve meat quality, rumen fermentation, and rumen bacterial community structure in sheep. The recommended dietary inclusion level of LRL ranges from 5% to 15%.