Dihydroquercetin, the antioxidant added to the sheep diet either alone or in combination with organic iodine had a significant effect on the rumen enzymatic and microbiological processes, the intermediary metabolism, and the sheep’s resistance. Under the effect of dihydroquercetin in combination with the organic iodine, insignificant increases in the chyme’s pH, the advanced oxidation processes, the elevated level of ammonia, and the greater number of microorganisms in the rumen were recorded generally due to infuzoria. In case of adding dihydroquercetin alone, the chyme’s pH normalized, its oxidation lowered, the reduction processes intensified, and the microorganism number increased due to infuzoria and bacteria. Some decreases in the chyme concentrations of volatile fatty acids and ammonia were simultaneously observed. The feed additives had a significant impact on the rumen microbiota. Under the effect of dihydroquercetin in combination with the organic iodine, the numbers of lactobacilli and mesophilic aerobic and facultatively anaerobic microorganisms (MAFAnM) in the rumen content increased tenfold and fourfold, respectively, while the rumen lactose-positive strains and fungal species, including the fungi of the genus Candida, the molds, and the yeasts, decreased by 98.9 and 65.3%, respectively. In case of adding dihydroquercetin alone, the numbers of lactobacilli and MAFAnM increased 11.5-fold and 21-fold, respectively, while the lactose-positive strains decreased by 92.2%. The numbers of fungal species, including fungi, molds, and yeasts, increased 2.2-fold. Under the effect of dihydroquercetin in combination with the organic iodine, the serum globulin concentrations increased, while the levels of triglycerides and bilirubin and the ALT and AST activities lowered in the sheep blood. In case of adding dihydroquercetin alone, the increases in serum albumin concentration, together with the globulin concentrations, were recorded. Therefore, the albumin-globulin ratio comprised 0.99. The levels of triglycerides and bilirubin and the ALT and AST activities also lowered. Dihydroquercetin in combination with the organic iodine and alone lowered the white blood cell count by 22.7 and 27.1%, respectively, increased the red blood cell count by 13.9 and 16.5%, respectively, and elevated the hematocrit level, indicating the sheep’s health improvements.