This study aimed to assess the variation over time in thermal comfort indices and the behavior of physiological parameters related to thermolysis, blood parameters, and semen in natura of buffalo bulls reared in tropical climate. The study was carried out in an artificial insemination station under a humid tropical climate (Afi according to Köppen). Ten water buffalo bulls (Bubalus bubalis) were used during the 5 months (April to August) of study. The environmental Temperature Humidity Index (THId) and the pen microclimate Temperature Humidity Index (THIp) were calculated. Every 25 days, respiratory rate (RR), heart rate (HR), rectal temperature (RT), and Benezra's thermal comfort index (BTCI) were assessed in the morning and in the afternoon. A blood assay was performed every month, while semen was collected weekly. THIp did not vary over the months (P > 0.05) and was higher in the afternoon than in the morning (77.7 ± 2.6 versus 81.8 ± 2.1, P < 0.05). RR, HR, and BTCI significantly increased over the months and were different between the periods of the day (P > 0.05) but within the physiological limits. RT varied between the periods of the day and decreased over the months, being the lowest in August (37.8 ± 0.7 °C), time-impacted hematocrit, mean corpuscular volume, hemoglobin levels, and spermatic gross motility and vigor (P < 0.05). Thus, buffalo bulls reared under a humid tropical climate may have variations in thermal comfort during the hotter periods but are able to efficiently activate thermoregulatory mechanisms and maintain homeothermy, hence preserving their physiological and seminal parameters at normal levels.
It is believed that increased livestock production is limited by tropical climate. Thermal imbalance in bulls can lead to hyperthermia and alter testicular metabolism, causing subfertility or infertility. Therefore, the thermoregulation of composite Canchim bulls (5/8 Charolais × 3/8 Zebu) raised in tropical climate as well as their consequences in the physiological, hematological, hormonal, and andrological parameters were evaluated monthly. The bulls (n = 18; 30.0 ± 1.5 months; 503.8 ± 23.0 kg) were kept on pasture, in a single group, from August 2015 to March 2016, comprising the winter, spring, and summer seasons. Biometeorological variables were continuously monitored, and the Temperature and Humidity Index (THI) was calculated. A greater thermal challenge occurred in spring and summer (THI ≥ 72.0). Nevertheless, the bulls exhibited normothermia (38.6 to 38.9 °C) in these seasons. The cortisol did not vary between seasons (7.0 vs. 8.7 vs. 6.8 ng/mL; P > 0.05) and remained within the physiological patterns. Independent of the seasons, stress leukogram was also not observed, refuting the incidence of acute or chronic thermal stress. It is noteworthy that T3 and testosterone increased (P < 0.0001, P < 0.05) in spring and summer, the time that coincides with the breeding season, when there is increased metabolic requirement from the bulls. The progressive thermal challenge increase did not affect the scrotal thermoregulatory capacity, and in general, scrotal temperature remained at 5.2 °C below the internal body temperature. In summer, there was a 5% reduction in the minor sperm defects (P < 0.05) and DNA fragmentation in 2.4% of spermatozoa, a compatible value for high fertility bulls. The results show that the studied composite bulls can be considered as climatically adapted and constitute a viable alternative to be used in production systems in a tropical climate, even if the breeding seasons occur during the most critical thermal condition periods of the year.
Foi analisado o efeito de dois sistemas silvipastoris nos índices de conforto ambiental e alterações nos parâmetros fisiológicos de bezerros bubalinos criados na Embrapa Amazônia Oriental, Belém-PA (clima Afi), no Período 1 (abril a setembro/2007) e Período 2 (outubro/2007 a março/2008). Foram inseridos onze bezerros no Sistema Silvipastoril 1 (SSP1), que apresentava sombreamento útil nas pastagens de 18 a 21%, e oito no Sistema Silvipastoril 2 (SSP2), sem sombreamento, com lago para banho. Foram mensuradas as variáveis fisiológicas: temperatura retal (TR), frequência respiratória (FR), temperatura da pele (TP), e calculados o Índice de Temperatura e Umidade (ITU) e Índice de Conforto de Benezra (ICB), nos dois períodos experimentais, comparados pelo Teste Tukey (P < 0,05). O ITU apresentou diferença estatística entre horários (P < 0,05) e período do ano (P < 0,05), e oscilou de 73,5 ± 1,3 até 82,2 ± 0,8. A TR apresentou diferença estatística entre horários e períodos do ano (P < 0,05), com amplitude de 38,3 ± 0,26 a 39,3 ± 0,38 °C. A FR apresentou diferença significativa entre horários (P < 0,05), com amplitude de 32,2 ± 9,2 a 56,5 ± 19,0 mov min-1, consideradas acima dos níveis normais, enquanto a TP foi diferente estatisticamente entre períodos e horários (P < 0,05) e variou de 23,6 ± 8,3 a 31,7 ± 5,4 °C. Nos Períodos 1 e 2 e nos dois SSP's, os ICBs estiveram acima do valor ideal, variando de 2,46 ± 0,33 a 3,31 ± 0,62 (SSP1) e 2,42 ± 0,30 a 3,45 ± 0,66 (SSP2).
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