This study aimed to investigate the residual activity ofganophosphorus insecticides in cow’s farm under normal conditions ofeding and spraying program . Its objective was determination ofganophosphorus insecticide residues in animal feed (green fodder andncentrated mixture) and, in turn , their build up in milk as an endroduct. Samples were collected during winter and summer seasons 1993-94. This study , on the other hand, was initiated to elucidate the effectDiazinon as one of the most common used organophosphorussecticides in veterinary field on serum cholinesterase and serum calciumcattle after spraying with the recommended dose of the drug (0.01 %) .respectively. While it was 90% in C.lazera fed on diet