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It is well known that a bull's testes must be cooler than body temperature and that increased testicular temperature reduces motile and morphologically sperm and their fertility. Regarding pathogenesis of increased testicular temperature on spermatogenesis, there is a long-standing belief that the bovine testis is almost hypoxic, increased testicular temperature increases O2 use but testicular blood flow does not change, resulting in hypoxia that causes morphologically abnormal sperm with decreased motility and fertility. Despite being widely accepted, there are limited experimental data to support this mechanism. However, scientific data shows that hyperoxia was not protective and hypoxia did not replicate changes, making us doubt that testicular hypothermia causes hypoxia. Elucidating the true pathophysiology of testicular hyperthermia is absolutely essential to developing evidence-based approaches to prevent or reduce effects of heat stress on spermatogenesis in bulls. In two recent studies using anesthetized rams, it was measured testicular blood flow, O2 delivery and uptake and temperature. In the first study, rams were exposed to three O2 concentrations (100% (hyperoxia); 21% (normoxia) and 13% (hypoxia). Under hypoxic conditions, the testis maintained O2 delivery and uptake by increasing blood flow and O2 extraction, without anaerobic metabolism. In the second study, testicular temperatures were increased (33, 37 and 40 ºC), resulting in increased blood flow and O2 extraction with no indications of testicular hypoxia or anaerobic metabolism. Therefore, these recent data challenged the paradigm that testicular hyperthermia does not increase testicular blood flow and as a result, hypoxia disrupts spermatogenesis.Morphologically abnormal sperm and subfertility are common in bulls, with testicular hyperthermia often blamed or suspected. High ambient temperatures reduce semen quality in male mammals. The situation is becoming increasingly common, due to climate change, emphasizing the need to understand the pathogenesis of testicular hyperthermia. Although Bos indicus bulls have much greater resistance than Bos taurus bulls to heat stress, including effects on spermatogenesis, specific mechanisms remain unclear. Therefore, there is a need to determine breed differences in susceptibility to increased testicular temperature. Our objectives are to compare responses between Bos indicus and Bos taurus bulls regarding testicular blood flow, O2 delivery and uptake, and lactate production (hypoxia marker) following mild testicular heat stress. We hypothesize that B. indicus bulls have better ability than B. taurus bulls to modulate testicular blood flow and O2 delivery in response to mild testicular heat stress.Bulls (12 B. indicus and 12 B. taurus) will be anesthetized and surgery done to place a testicular blood flow probe and catheters. Bull testes will be heated to 33, 37 and 40ºC. Blood flow will be measured and blood samples (arterial and venous) will be collected, and evaluated for blood gases and lactate (marker of hypoxia), enabling us to measure delivery and uptake of O2 by testes.The proposed work is very novel and will be conducted by highly skilled experts, in a true collaboration, using state-of-the-art methods. This study brings together experts in anesthesia (Dr. Francisco T Neto), surgery (Dr. Carlos A Husni) and animal reproduction (Drs. John Kastelic and João C P Ferreira), and forms part of the PhD thesis work of Guilherme Rizzoto. Given our expertise and that we are using approaches similar to our previous studies in rams, we are confident of success in generating novel data that can be published in high-ranking international journals. Furthermore, we expect that this work will be followed by additional collaborative studies in this area. (AU)

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Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
RIZZOTO, G.; FERREIRA, J. C. P.; MOGOLLON GARCIA, H. D.; TEIXEIRA-NETO, F. J.; BARDELLA, L. C.; MARTINS, C. L.; SILVA, J. R. B.; THUNDATHIL, J. C.; KASTELIC, J. P.. Short-term testicular warming under anesthesia causes similar increases in testicular blood flow in Bos taurus versus Bos indicus bulls, but no apparent hypoxia. Theriogenology, v. 145, p. 94-99, . (18/02007-6)
RIZZOTO, GUILHERME; ROSSI, EDUARDO S.; PUPULIM, ANTONIO G. R.; CODOGNOTO, VIVIANE M.; CARVALHO, JAQUELINE C.; TEIXEIRA, MARINA B.; RATTES, PAULA Z.; THUNDATHIL, JACOB C.; KASTELIC, JOHN P.; FERREIRA, JOAO C. P.. New insights in testicular and sperm impacts after testicular heat stress in ruminants. Animal Reproduction Science, v. 247, p. 1-pg., . (18/02007-6)
RIZZOTO, G.; FERREIRA, J. C. P.; CODOGNOTO, V. M.; OLIVEIRA, K. C.; MOGOLLON GARCIA, H. D.; PUPULIM, A. G. R.; TEIXEIRA-NETO, F. J.; CASTILHO, A.; NUNES, S. G.; THUNDATHIL, J. C.; et al. Testicular hyperthermia reduces testosterone concentrations and alters gene expression in testes of Nelore bulls. Theriogenology, v. 152, p. 64-68, . (18/02007-6)

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