MALE REPRODUCTIVE DISORDERS
Generally, about 5-10% of cattle bulls reaching sexual maturity would be suffering from poor reproductive efficiency or sterility. Crossbreeding has brought in its wake an additional problem related to male infertility. Domesticated cattle, classified into two major groups, zebu (Bos indicus) and European (Bos taurus) are believed to descend from the same wild species, the Aurox (Bos primigenius). Most of the cattle indigenous to the tropics belong to the zebu species. The potential for milk production is poorly developed in most zebu cattle. As various countries tackle the challenge of increasing the productivity of their dairy cow populations, the substantial genetic difference in milk production potential between Bos indicus breeds and Bos taurus breeds is too large to go unnoticed. Hence, application of artificial insemination has made crossbreeding between Bos taurus and Bos indicus populations widely possible for substantial increase in milk yield. However, the male crossbred offsprings are often inferior to purebreds in semen production. The proportion of males reserved for breeding and reaching successful semen freezing stage was lowest (29%) in Karan Fries (cross between Sahiwal or Tharparkar with Holstein Freisian cattle) and highest (45%) in Sahiwal cattle and poor semen quality was an important reason of disposal in Karan Fries bulls. Poor semen quality has been found to be the main reason of disposal in adult breeding Karan Fries bulls above 3 years of age. The relative importance of the bull in achieving high standards of fertility is tremendous to the extent that it is often said that the bull is half the herd.
Sub-fertility and sterility in bulls could emanate from genetic congenital abnormalities or developed during its lifetime.