Abstract
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.
Highlights
All procedures were performed following the rules issued by the National Council for Control of Animal Experimentation (CONCEA), following the ARRIVE guidelines, and was approved by the Ethics Committee on Animal Experimentation of the Faculty of Animal Science and Food Engineering, University of São Paulo (Protocol #4400100621)
We calculated the Temperature and Humidity Index (THI) to compare with Black Globe and Humidity Index (BGHI) in terms of heat tolerance
Mader et al (2010) showed that BGHI might be a better indicator of heat stress because BGT is susceptible to wind speed because black globe temperature is related to the radiant temperature, to which the animal is susceptible
Summary
The physiological consequences of heat stress in males are often studied by increasing testicular temperature, which is usually induced artificially, for example, by scrotal bags or insulation (GarciaOliveros et al, 2020; Newton et al, 2009; Rahman et al, 2011) or using hot rooms or heating semen (Peña Junior et al, 2021); naturally high environmental temperatures have been shown to disrupt the male reproductive physiology in the different species (Li et al, 2020; Rasooli et al, 2010; Seifi-Jamadi et al, 2020). Breed differences, in special regarding ability (beef x milk), and farming systems (housed x grass based) are essential figures to be mainly analyzed for each herd and purpose
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