Potential risk of thermal stress for Bradford bulls in Brazilian tropical and subtropical regions
Thermal stress imparts physical and economical losses to livestock production in temperate, subtropical and tropical regions of the world. The Temperature and Humidity Index (THI) was brought as an option to evaluate the morphological changes from bull semen according to environmental stress. The objective of this work was to evaluate the reproductive performance in Braford bulls, through the seminal quality, using THI as an environmental stress in the tropical and subtropical regions in Brazilian. We used Braford bulls from 5 different experiments, three farms located at the subtropical Brazilian region and two at the tropical. Semen collections were performed at least once a month through the experimental periods. Climate data was analysed 18 and 12 days prior to sampling corresponding to the spermiogenesis and the epidydimal transit period. The data was analysed through ANOVA, means differentiated through Tukey test and p-value was set at >0.05. The subtropical and tropical region presented significant differences within the area studied and specially when suggesting a climate zoning for animal production. The percentage of days categorized as harmful was significant for both regions and its correlated to the total and major sperm defects, representing the importance of environmental changes as a stressor to sperm. Both regions showed a significant variation between seasons that classified the summer and the hot humid period as more stressful impact on the animal growth and well-being. The Braford genetic, being a mixed of Bos taurus indicus and Bos taurus taurus, would be a potential breed to be adapted to the tropics, however a quantification of weather effect is difficult to achieve accuracy on the acclimatization process, variance between individuals, different farm management and changes in the combination of environmental factors.