It is possible that Brahman cattle are less pure zebu (B. t. indicus) than Nelore cattle. Considering
that a limited number of zebu animals (mainly Guzerat, Gir and Nellore breeds) were imported and
that there are records of less than 300 imported Brahmans in USA, most of which were bulls, it must
be assumed that other breeds supplied the foundation animals for the breed. The bulls were used
on cows of the European breeds and on the descendants of the crosses. By the fifth generation the
offspring carried not only a preponderance of indicus breeding but selection pressure had permitted
the development of an animal generally regarded as superior to the original imports for beef production.
Conversely, Nelore breed was originated primarily from Ongole (indicus) breed from India
(http://www.ansi.okstated.edu/breeds/cattle). Therefore, if the Brahman is less indicus than Nelore
breed it is conceivable that Brahman bulls may be less effective in increasing resistance of crossbred
embryos (Holstein×Brahman) to heat shock.