The effect of internal and external parasitism on productivity of dairy cattle is considered as the most unidentifiable underlying cause for low productivity. Parasites are found externally viz., ticks, mites, flies and internally such as worms, protozoa etc., are a major cause of disease and production loss. Various species of protozoans and helminths cause economically important parasitic diseases with economic loss by decrease in milk production, decreased weight gain, treatment costs and mortality. While abortion losses, organ condemnation, carcass weight loss and decreases hide value, and fecundity are other effects. A major concern in the control of parasitic diseases is the development of resistance by worms, flies, ticks etc. The parasitic challenge experienced and the outcome of that challenge is a dynamic one in which environment, management practices, including housing or grazing management, nutritional status, the host's ability to develop effective immunity and the speed with which this can occur, play a significant role.