Effects of fermented mulberry leaves on rumen fermentation and microbiota in rumen fluid of heat-stressed Hu sheep.

Heat stress is a major abiotic stress that limits growth performance, health, and physiological responses of sheep. Although Hu sheep possess innate mechanisms for managing heat stress, prolonged exposure impairs their performance and health. Rumen microbiota served as key players in responding to environmental fluctuations and mediating major regulatory functions. This study was conducted to explore the effects of different proportions of concentrate replaced with fermented mulberry leaves (FML) on rumen fermentation and bacterial and fungal community structures in rumen fluid in Hu sheep. A total of 45 Hu sheep with similar body weight (26.42 ± 3.57 kg) were randomly divided into three groups: the control group (CONT) was fed a basal diet, and the treatment groups (FML Treatment) FT1 and FT2 were fed experimental diets in which 10% and 20% concentrate, respectively, were replaced by FML. The pretest lasted for 7 days, and the formal period lasted for 90 days. The average daily gain in the FT1 group increased at the first month of the formal period compared to the CONT group (P < 0.05). Lower feed conversion ratio, feed weight gain cost (P < 0.05), and higher apparent digestibility of acid detergent fiber and crude protein (P < 0.05) were observed in the FT1 group. Moreover, the concentrations of acetate, propionate, valerate, and ammonia nitrogen in the FT1 group were significantly higher than those in the CONT group (P < 0.05). Further analysis of the rumen microbiota indicated that the relative abundance of Succiniaclassicum and Eubacterium_ventriosum_group decreased, whereas that of Prevotellaceae_UCG_003 and unclassified_Selenomonadaceae increased in the FT1 group. Internal transcribed spacer sequencing indicated that FML significantly increased the relative abundance of beneficial fungi in the rumen of heat-stressed Hu sheep, including Aspergillus_alabamensis, Aspergillus_versicolor, Aspergillus_flavus, and Candida in the FT1 group. Correlation analysis suggested that the apparent digestibility of nutrients in fattening Hu sheep under heat stress was highly correlated with bacteria. Our findings indicate that the replacement of concentrate with FML can improve production performance, increase the apparent digestibility of nutrients, and enhance the rumen fermentation efficiency of fattening Hu sheep under heat stress. These changes are highly correlated with the changes in the composition and structure of bacteria and fungi in the rumen fluid. KEY POINTS: 10% FML Treatment enhanced feed conversion ratio and nutrient digestibility. 10% FML Treatment enhanced the rumen fermentation efficiency. 10% FML Treatment altered bacterial and fungal structures in rumen fluid.