Sahiwal is one of the best milch breeds of India known for its higher milk production, remarkable power of endurance for hot climate of tropics, resistance to tropical diseases, low cost of maintenance and higher feed conversion efficiency. Development of a suitable breeding strategy for genetic improvement of dairy animals depends upon a fair understanding of the genetic and phenotypic parameters like milk production trait. Milk production during the entire lactation is a continuous physiological function which describes the rate of milk secretion with advancement in lactation. The selection of genetically superior sires is the back bone of any breed improvement program. The success of any breed improvement program depends on how early and accurately young bulls can be evaluated.