author(s)
BC Naha, AK Chakravarty, MA Mir, BL Saini, P Boro and Supradip Das

abstract
Fertility means the ability of an animal to produce young one. Fertility of a herd is depended mainly on early sexual maturity of animal, timely heat detection, less breeding interval, conception rate and number of services per conception. Bull fertility helps in improving the herd productive and reproductive performance. Till date, most fertility related studies in dairy animals have done on female fertility but male fertility has not been completely investigated. Optimizing the age of breeding bulls in relation to their fertility will help in the selection and use of breeding bulls in right age that will improve the herd reproductive efficiency. In India sire conception rate in relation to optimize the age of service sires has not been completely investigated. Keeping the importance of improving the fertility in Sahiwal bulls, the present investigation has been proposed.