Background: During perinatal period, the immune system of calves is developing, making them vulnerable to infectious diseases that affect their growth or increasing mortality. Phytobiotics have various physiological effects on animals that could improve their performance and health. In this study, the effect of a feed herbal mixture made from Azadirachta indica and Phyllanthus niruri were evaluated in dairy calves. Methods: Forty Holstein calves were assigned into four groups (doses of 0, 2, 3 and 4 g d-1) and productive and health parameters were recorded. Results were analyzed according to a completely randomized design in which linear and quadratic effects of daily feed additive dose were tested. Result: Increasing the dose of herbal mixture linearly reduced final body weight, body weight gain and daily calve starter intake, although it improved feed conversion. Blood tests showed that hematocrit and hemoglobin increased quadratically. The number of segmented neutrophils increased linearly. Finally, the number of pneumonia cases decreased quadratically. These results suggest that supplementation with herbal additives could improve feed efficiency and improve the health status of calves.