Faced to the need to produce more meat and with better quality, synthetic breeds such
as Braford have gained space in the national livestock. The intense heat stress is the
main cause of the decrease in the reproductive performance of bulls raised in tropical
climate, so the adaptation of the bulls to this climate is indispensable to guarantee its
fertility. In order to determine the of physical and functional characteristics of semen
from Braford and Nelore bulls raised in tropical region, semen samples were used of
15 Braford bulls and 8 Nellore bulls, all of them extensively raised. Three collections
of semen were performed, with a 2-month interval between each collection, and
conventional tests were performed: volume, appearance, swirling, progressive motility,
vigor, concentration and sperm morphology; and functional tests: evaluation of plasma
membrane integrity (EOS-NIG), evaluation of the integrity of the acrosomal membrane
(POPE) and evaluation of mitochondrial cytochemical activity (DAB). The mean
temperature and humidity index (TUI) of the period of 30 days before each collection
was obtained. There was no significant difference between the races in plasma
membrane integrity, the mean spermatozoa of Braford bulls with whole plasma
membrane was 52.01% while that of Nelore bulls was 36.49%. In relation to the
integrity of the acrosomal membrane there was also no significant difference between
the two genetic groups, the average found for Braford bulls was 98.37% and for Nellore
bulls was 99.24%. There was no significant difference between the breeds in relation
to the mitochondrial cytochemical activity, in both cases there was a higher prevalence
of class II spermatozoa, and the average found for Braford bulls was 87.45% of class
II spermatozoa, and for Nelore bulls of 93.02%. Nelore bulls showed good seminal
quality in all piglets, while Braford bulls showed a decrease at the end of the breeding
season.
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