The objective of this dissertation was to investigate if dietary supplements could improve dairy calf health and welfare. The first study was focused on investigating the effects of Echinacea purpurea (EP) supplementation on markers of immunity, health, feed intake, and growth of dairy calves. Overall, EP supplementation was associated with blood markers indicative of reduced inflammation and stimulated immunity, with minor benefits to health and growth. The second study was focused on how weaning, as well as supplementing calves with tyndallized Lactobacillus helveticus (TLH), affects behavioral and physiological indicators of dairy calf affective state. Overall, there were changes in the behavior of calves at weaning that were indicative of a more negative affective state. Supplementation of TLH was associated with indicators of a more negative affective state, especially during weaning. In summary, this research provides novel information on the effects of dietary supplements on dairy calf health and welfare.