Effects of a mixture of phytobiotic-rich herbal extracts on growth performance, blood metabolites, rumen fermentation, and bacterial population of dairy calves

Forty-eight newborn Holstein dairy calves [40 ± 3.4 (SD) of kg of body weight (BW); 24 females and 24 males] were used in a completely randomized design to investigate the effects of a mixture of phytobiotic-rich herbal extract (Immunofin, IMPE) incorporated into milk on performance, ruminal fermentation, bacterial population, and serum biochemical metabolites during the preweaning period. Calves had free access to calf starter and clean water from d 6 until weaning. The treatments were the control (CON; without additive) and IMPE at 4, 8, and 12 mL/d. The treatments had no significant effect on total dry matter intake, weight gain, and BW at weaning. The incidence of diarrhea was lower in calves fed 8 mL of IMPE/d compared with CON. At weaning, body measurements (except for front leg circumference) were not affected by IMPE treatment. Relative to the CON group, front leg circumference was significantly decreased by IMPE supplementation. Serum IgG concentration was not significantly increased by IMPE supplementation compared with the CON group. Triglyceride concentration decreased in calves receiving 4, 8, and 12 mL/d of IMPE compared with the CON groups. In contrast to the CON group, serum albumin and total serum protein concentrations increased with IMPE supplementation. Calves receiving 4 mL/d of IMPE had a greater abundance of total bacteria, Ruminococcus albus, Ruminococcus flavefaciens, and Fibrobacter succinogenes compared with the other treatments. Molar proportions of acetate increased in calves fed IMPE (at 12 mL/d) compared with calves fed CON. Ruminal N-NH₃ concentrations decreased linearly with the increase in IMPE supplementation. The results of the present study suggest that the addition of IMPE to milk may improve some health and immunity conditions, blood metabolite concentrations, and increase the abundance of some cellulolytic bacteria in the rumen of Holstein dairy calves. The use of IMPE may be an alternative to feeding antibiotics at subtherapeutic concentrations to improve calf health and immunity status.