Effects of a Defined Blend of Phytochemicals on Growth Performance, Rumen Fermentation, Bacterial Diversity, and Blood Biochemical and Physiological Parameters in Altay Sheep

This study aimed to evaluate the effects of dietary supplementation with a defined blend of phytochemicals (DBP) composed of carvacrol, thymol, and cinnamaldehyde on the growth performance, slaughter performance, rumen fermentation, microbial diversity, and blood physiological and biochemical parameters of sheep. Twenty-four healthy male Altay lambs, aged six months, were randomly assigned to three groups: (1) fed a basal diet (CON), (2) basal diet with 400 mg/kg DM of DBP (DBP1), and (3) basal diet with 800 mg/kg DM of DBP (DBP2). Results show that DBP supplementation had no significant effect on growth or slaughter performance (p > 0.05). The molar proportion of acetate and the acetate-to-propionate ratio increased linearly, and the molar proportions of propionate and valerate decreased linearly (p < 0.05). DBP supplementation had no significant effect on rumen bacterial α-diversity; however, in the DBP1 group, the relative abundances of Succinivibrionaceae UCG-002, Prevotellaceae UCG-004, Sphaerochaeta, Monoglobus, and Moryella were significantly increased, whereas in the DBP2 group, the relative abundances of Coprococcus and U29-B03 were significantly increased (p < 0.05). DBP exhibited a significant quadratic effect on interleukin-2 and superoxide dismutase activity (p < 0.05). In conclusion, although the DBP altered the rumen microbial community structure and rumen fermentation pattern in sheep to some extent, it showed minimal efficacy in improving growth performance, slaughter performance, immune function, and antioxidant status. Further large-scale studies are warranted to determine the optimal inclusion level and timing of this phytochemical blend in sheep diets.