In India, the dairy industries are mainly dependent on cattle and buffalo milk; therefore, cattle and buffalo breeding bulls are considered as dairy bulls. Infertility and reduced fertility in animals are because of many reasons but chromosomal aberrations could also be one of the reasons. Cytogenetic investigations were carried out on a group of 57 dairy bulls of different age group. Lymphocyte culture revealed that a few samples showed sporadic chromosomal aberrations like chromosome fragmentation, polyploidy and premature centromeric division (PCD) in metaphase chromosomes of dairy bulls which may not have direct relevance on fertility as such aberrations were not consistent.. However, one sample each of cattle and buffalo bull exhibited low degree of sex chromosome mosaicism (60,XY/61,XYY) and autosomal mosaicism (50,XY/51,XY) respectively. The bulls exhibiting mosaicism are mature and in semen collection at different places, indicating that both bulls are fertile. In such cases the fertility of bull as compare to normal bull, must be slightly reduced that is not probably noticed by the Manager of sperm stations as fertility index of bull based on their field AI performance are not regularly monitored. 1320750403.php