RESUMO
Testicular degeneration by heat is the leading cause of infertility in bulls. Beef cattle are generally farmed under hot and humid conditions, and consequently, the thermotolerance of each breed must be considered in their natural environment. This study aimed to evaluate the reproductive characteristics of Brahman bulls maintained in the grazing system, with or without shadow availability. Ten Brahman bulls aging between 24 and 30 months were allocated in two different paddocks, with or without shadow availability. The heat tolerance test was performed on three non-consecutive typical summer days. The semen samples were collected at four times points in a 14 days interval. The climate conditions were monitored throughout the experiment; and clinical evaluation, testicular consistence and scrotal circumference were measured before every semen collection. In addition, semen was evaluated regarding volume, aspect, turbulence, motility, straight movement, sperm concentration, and morphological exam. The studied Brahman bulls showed a high thermolysis capacity, high heat tolerance, and no differences in semen quality were observed between groups.
A degeneração testicular causada pelo calor é a principal causa de infertilidade em touros. Bovinos de corte geralmente são criados em condições de calor e umidade, e, consequentemente, a termotolerância de cada raça deve ser considerada em seu ambiente natural. O presente trabalho teve como objetivo avaliar as características reprodutivas de touros da raça Brahman mantidos em sistema de pastejo, com ou sem disponibilidade de sombra. Dez touros Brahman com idades entre 24 e 30 meses foram alocados em dois piquetes diferentes, com ou sem disponibilidade de sombra. O teste de tolerância ao calor foi realizado em três dias típicos de verão não consecutivos. As amostras de sêmen foram coletadas em quatro momentos em intervalos de 14 dias. As condições climáticas foram monitoradas durante todo o período experimental; e a avaliação clínica, consistência testicular e a circunferência escrotal foram avaliadas antes de cada coleta de sêmen. Ainda, o sêmen foi avaliado quanto ao volume, aspecto, turbulência, motilidade, vigor, concentração espermática e exame morfológico. Os touros estudados da raça Brahman apresentaram alta capacidade de termólise, alta tolerância ao calor, e não foram observadas diferenças na qualidade do sêmen entre os grupos.
RESUMO
Adaptation is a relevant characteristic to be understood in livestock animals in order to maintain and raise productivity. In Brazil, the Nellore beef cattle are widely disseminated and well-adapted breed that present good thermoregulatory characteristics for tropical environment conditions. Conversely, the physiological and cellular mechanisms required for thermoregulation and thermotolerance in this breed are still limited. The aim of this study was to comprehend the heat loss efficiency at the whole animal level and heat shock response at the cellular level of Nellore cows in tropical climate conditions. Healthy purebred Nellore cows were classified according to their capacity to lose body heat as Efficient or Inefficient based on vaginal temperature which was continuously monitored by data-loggers. Rectal, tail, and ocular temperatures, sweating rate, and respiratory frequency were collected to assess other thermoregulatory responses. Peripheral mononuclear cells were used for gene expression of heat shock proteins 60, 70, and 90 induced by in vitro heat treatments at 38, 40, and 42 °C. In our findings, the Efficient cows presented higher sweating rates compared to Inefficient cows that presented higher rectal temperature with greater amplitude of vaginal temperature profile. Transcription of the HSP genes was stable at 38 and 40 °C and decreased for all HSP genes at 42 °C. In conclusion, the Nellore efficiency to lose heat was mainly associated with their sweating capacity and cellular thermotolerance confirmed by the maintenance of heat shock proteins transcripts under heat stress. Taken together, this knowledge contributes as a future key for genetic selection of adapted animals.
