Fermented Chinese herbal medicines combined with probiotics promote growth of fattening lambs under heat stress by modulating rumen mucosal barrier functions

Heat stress (HS) has caused substantial economic losses in the livestock industry, Chinese herbal medicines (CHMs) have been demonstrated significant potential in mitigating HS. The objective of this study was to evaluate the effects of dietary fermented Chinese herbal medicines (FCHM) on growth performance in fattening lambs under HS and rumen mucosal barrier including mechanical, chemical, immune, and microbial barriers. One hundred sixty 4-month-old male fattening lambs (northeast fine-wool sheep × small-tail Han sheep, initial weight of 37.17 ± 0.44 kg) were randomly allocated into four groups. Each group included four replicates with 10 lambs per replicate, supplied with 0 % (control group), 0.5 %, 1.0 %, or 1.5 % FCHM in the diet. During the entire trial period of 90 days, temperature and humidity index in experimental shed averaged 72.73, under which lambs were suffering from HS. Average daily gain (ADG) showed an increase in the 1.0 % (P = 0.026) or 1.5 % (P = 0.003) FCHM group over the entire period, compared to the control, and dry matter intake in the 1.5 % group also increased (P = 0.009). From mechanical barrier in rumen mucosa, papilla length (All P < 0.001) and papilla surface area were greater in the 1.0 % or 1.5 % groups (P = 0.005 or P = 0.007) than that in control. The mRNA expression levels of the tight junction proteins (Claudin-1, Claudin-4, and Occludin) were up-regulated (P < 0.05) in all FCHM-supplemented groups. From chemical barrier, pH value in rumen fluid demonstrated an increase (P = 0.021) in the 1.0 % group, while acetic acid concentrations decreased (P < 0.05) in all FCHM groups, compared to control. From immune barrier, when FCHM was offered to lambs, secretory immunoglobulin A concentrations in rumen mucosa increased (P < 0.05), while mRNA expressions of interleukin-6 and Toll-like 4 receptor were down-regulated (P < 0.001). Also, serum interleukin-1β concentrations were lower (P < 0.001) in the 0.5 % or 1.0 % groups than control. For microbial barrier, diversity and abundance of rumen bacterial community were evaluated. Number of bacterial operational taxonomic units showed an increasing trend (P = 0.061) with FCHM. Moreover, relative abundance of Proteobacteria was increased (P = 0.010) by the 1.5 % FCHM, and the abundances of Prevotellaceae_UCG_003 was increased while Lachnospiraceae_NK3A20_group were decreased (all P < 0.05) by the 1.0 % FCHM. Furthermore, PICRUSt2 functional predictions for metabolic pathway suggest that FCHM supplements influenced carbohydrate, cofactor, and vitamin metabolism (P < 0.05). In summary, dietary FCHM supplements could improve rumen mucosal barrier, thereby alleviating HS in fattening lambs.