Question: query regarding use of anthalmintic in calf 
Answer: it is advisable to give anthalmintic at the age offore month, but  feed additives containing anthalmintic can be used before 4 months of age to reduce the  effect of parasitic infestation, organogenesis in case of calf is complete at the age of four months after birth [ like the stomach, particularly the rumen develope start & complete at the age of four month ] if anthalmintic is used the it may effect the organogenesis affecting the germinating cells   ,resulting the digestive & productive performance [ in case of female ] in future