This book highlights the relationship between prolactin gene variants with milk production traits in three indigenous breeds of cattle. Out of which two are drought type and only one milch type i.e., Frieswal breed developed by crossing Holstein Friesian with Sahiwal cows at Military Dairy Farms under the Ministry of Defence in collaboration with the Ministry of Agriculture launched a Cattle Breeding Project at Meerut in the year, 1985 for fulfilling the demand of milk in India.