RESUMO

Estudos sobre estresse térmico em equinos, geralmente envolvem condições induzidas pelo exercício físico intenso, assim como as alterações fisiológicas que comtemplam o efeito do ambiente em geral são relacionadas ao fotoperíodo e não ao efeito da temperatura como acontece com maior frequência em outras espécies. Verifica-se uma necessidade de maior compreensão dos efeitos deletérios do estresse térmico no desempenho reprodutivo desta espécie, visto que a produção de potros saudáveis é o objetivo de um programa reprodutivo e em geral a principal fonte de retorno econômico da atividade. Esse fato ganha ainda mais relevância diante das condições climáticas e de criação presentes nos trópicos, além da atividade reprodutiva da espécie equina depender de períodos de alta luminosidade ambiental, que coincidem com as maiores temperaturas. O presente trabalho tem por objetivo demonstrar como o estresse térmico ambiental pode promover a redução da fertilidade em fêmeas equinas e alertar para a necessidade de estudos completos envolvendo o tema.

Studies on thermal stress in equines usually involve conditions induced by intense physical exercise, as well as the physiological changes that contemplate the effect of the environment in general are related to the photoperiod and not to the effect of temperature as it in other species. We need a better understanding of the deleterious effects of thermal stress on the reproductive performance of this species, since the production of healthy foals is generally the objective of a reproductive program and the main source of economic return of the activity. This fact is even more relevant given the climatic and breeding conditions in the tropics, and the reproductive activity of the equine species take place on periods of high luminosity, which coincide with higher temperatures. The present review aims to demonstrate how the environmental thermal stress can promote the reduction of the fertility in equine females and to alert to the necessity of complete studies involving the theme.

Assuntos

RESUMO

Estudos sobre estresse térmico em equinos, geralmente envolvem condições induzidas pelo exercício físico intenso, assim como as alterações fisiológicas que comtemplam o efeito do ambiente em geral são relacionadas ao fotoperíodo e não ao efeito da temperatura como acontece com maior frequência em outras espécies. Verifica-se uma necessidade de maior compreensão dos efeitos deletérios do estresse térmico no desempenho reprodutivo desta espécie, visto que a produção de potros saudáveis é o objetivo de um programa reprodutivo e em geral a principal fonte de retorno econômico da atividade. Esse fato ganha ainda mais relevância diante das condições climáticas e de criação presentes nos trópicos, além da atividade reprodutiva da espécie equina depender de períodos de alta luminosidade ambiental, que coincidem com as maiores temperaturas. O presente trabalho tem por objetivo demonstrar como o estresse térmico ambiental pode promover a redução da fertilidade em fêmeas equinas e alertar para a necessidade de estudos completos envolvendo o tema.(AU)

Studies on thermal stress in equines usually involve conditions induced by intense physical exercise, as well as the physiological changes that contemplate the effect of the environment in general are related to the photoperiod and not to the effect of temperature as it in other species. We need a better understanding of the deleterious effects of thermal stress on the reproductive performance of this species, since the production of healthy foals is generally the objective of a reproductive program and the main source of economic return of the activity. This fact is even more relevant given the climatic and breeding conditions in the tropics, and the reproductive activity of the equine species take place on periods of high luminosity, which coincide with higher temperatures. The present review aims to demonstrate how the environmental thermal stress can promote the reduction of the fertility in equine females and to alert to the necessity of complete studies involving the theme.(AU)

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The effects of oxidative stress induced by high temperature on the cell viability, proliferation, apoptosis and oxidative status of chicken embryonic fibroblasts (CEF) were analyzed. The viability, proliferation, apoptotic and anti-oxidative status were measured after incubating CEF at the temperatures of 37ºC (control) and 40-44ºC (experimental groups) for 6,12 and 24 hours. The results showed that at high temperature (42-43ºC), the viability of CEF cells decreased after 6, 12 and 24 h of incubation, but the difference was significant only at 43ºC. Cell proliferation was significantly reduced at 44oC/6h. The apoptotic rate of CEF cells was increased following heat treatments in a time-dependent manner. ROS formation increased with increasing temperature, but the difference was only significant at 44ºC/6,12h. Heat stress did not significantly affect the superoxide dismutase (SOD) activity. CAT activity was significantly decreased at 43ºC/24h and 44ºC/12 and 24h. Malondialdehyde (MDA) formation was significantly increased at 43ºC/12h and 44ºC/12 and 24h. In conclusion, heat stress induced the oxidative stress, decreasing the viability, proliferation and anti-oxidative response of CEF cells.(AU)

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RESUMO

The effects of oxidative stress induced by high temperature on the cell viability, proliferation, apoptosis and oxidative status of chicken embryonic fibroblasts (CEF) were analyzed. The viability, proliferation, apoptotic and anti-oxidative status were measured after incubating CEF at the temperatures of 37ºC (control) and 40-44ºC (experimental groups) for 6,12 and 24 hours. The results showed that at high temperature (42-43ºC), the viability of CEF cells decreased after 6, 12 and 24 h of incubation, but the difference was significant only at 43ºC. Cell proliferation was significantly reduced at 44oC/6h. The apoptotic rate of CEF cells was increased following heat treatments in a time-dependent manner. ROS formation increased with increasing temperature, but the difference was only significant at 44ºC/6,12h. Heat stress did not significantly affect the superoxide dismutase (SOD) activity. CAT activity was significantly decreased at 43ºC/24h and 44ºC/12 and 24h. Malondialdehyde (MDA) formation was significantly increased at 43ºC/12h and 44ºC/12 and 24h. In conclusion, heat stress induced the oxidative stress, decreasing the viability, proliferation and anti-oxidative response of CEF cells.

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In Northern Patagonia, the mating season starts on March 15th, when rams are submitted to summer temperatures. Exposure of rams to heat stress increases the prevalence of microscopic damage to spermatozoa, morphological abnormalities, and reductions in fertility. This study assesses the adaptive capabilities of six unshorn and six shorn Australian Merino rams, half of which were treated in a heat chamber for eight hours for five days, gradually reaching a temperature of up to 40 °C. Microscopic damage, abnormalities and ultramicroscopic alterations of the plasma membrane and the acrosome of sperm head were analysed. There were significant differences in the percentage of tailless spermatozoa and proximal cytoplasmic droplets between post-treatment periods. Temperature primarily affected the shorn rams and the sperm heads during spermiogenesis. Submicroscopic alterations were observed when the plasma membrane was present in the anterior segment. These alterations can be intact, waved, or dilated. When the plasma membrane was absent, the acrosome might be intact, dilated, and waved. In addition, the outer acrosomal membrane may completely lose its contents or have a nude nucleus. The plasma membrane assumes a waved shape as a result of the effect of temperature on the epididymis. According to this study, the tailless head, proximal cytoplasmic droplets, and the ultramicroscopic categories studied were robust indicators of semen heat stress. After ten weeks, the sperm head recovered its normal shape. Unshorn rams are better adapted to summer heat stress than shorn ones. Microscopy and transmission electron microscopy alterations have been shown to be excellent indicators of thermal stress in Australian Merino rams and may be useful tools to help sheep farmers choose when to begin the mating season, which will vary depending on the environmental conditions of the summer.(AU)

Na Patagônia Norte, os ovinos têm sua estação de acasalamento iniciada em 15 de março, portanto, ficam sujeitos às temperaturas do verão. A exposição de carneiros a estresse térmico aumenta a prevalência de danos microscópicos e anomalias morfológicas nos espermatozoides, que implica uma redução na fertilidade. Este trabalho avaliou a capacidade adaptativa de carneiros Merino Australiano com lã (N = 6) e tosquiados (N = 6): metade ficou ao ar livre e outra metade foi mantida em uma câmara climática por oito horas, durante cinco dias, chegando gradualmente a uma temperatura máxima de 40 °C. Foram analisados danos microscópicos, anormalidades e alterações ultramicroscópicas da membrana plasmática e do acrossoma da cabeça dos espermatozoides. Os resultados microscópicos confirmaram a existência de diferença significativa na porcentagem de espermatozoides sem cauda e com gota citoplasmática proximal, entre os ejaculados pós-tratamento. A temperatura afetou os carneiros tosquiados, principalmente a cabeça de seus espermatozoides, durante a espermatogênese. Alterações submicroscópicas foram observados na membrana plasmática quando ela estava presente no segmento anterior: quando não intacta, ficava ondulada ou dilatada. Quando a membrana plasmática estava ausente, o acrossoma podia se apresentar ondulado ou dilatado. Além disso, sob efeito do calor, a membrana acrossomal externa pode perder completamente seu conteúdo ou apresentar núcleo desnudo. A membrana plasmática assume uma forma ondulada pelo efeito da temperatura no epidídimo. Depois de dez semanas, a cabeça dos espermatozoides recuperou sua forma normal. Como demonstrado neste estudo, a cabeça sem cauda, as gotas citoplasmáticas proximais e as categorias ultramicroscópicas estudadas são indicadores do efeito do estresse térmico no sêmen, e os carneiros com maior cobertura de lã se adaptam melhor ao estresse por calor. Alterações de microscopia e de microscopia eletrônica de transmissão têm se mostrado excelentes indicadores de estresse por calor em carneiros Merino Australiano e podem ser ferramentas úteis para ajudar criadores de ovelhas a escolher quando começar a época de acasalamento, o que irá variar de acordo com as condições ambientais do verão.(AU)

Assuntos

RESUMO

In Northern Patagonia, the mating season starts on March 15th, when rams are submitted to summer temperatures. Exposure of rams to heat stress increases the prevalence of microscopic damage to spermatozoa, morphological abnormalities, and reductions in fertility. This study assesses the adaptive capabilities of six unshorn and six shorn Australian Merino rams, half of which were treated in a heat chamber for eight hours for five days, gradually reaching a temperature of up to 40 °C. Microscopic damage, abnormalities and ultramicroscopic alterations of the plasma membrane and the acrosome of sperm head were analysed. There were significant differences in the percentage of tailless spermatozoa and proximal cytoplasmic droplets between post-treatment periods. Temperature primarily affected the shorn rams and the sperm heads during spermiogenesis. Submicroscopic alterations were observed when the plasma membrane was present in the anterior segment. These alterations can be intact, waved, or dilated. When the plasma membrane was absent, the acrosome might be intact, dilated, and waved. In addition, the outer acrosomal membrane may completely lose its contents or have a nude nucleus. The plasma membrane assumes a waved shape as a result of the effect of temperature on the epididymis. According to this study, the tailless head, proximal cytoplasmic droplets, and the ultramicroscopic categories studied were robust indicators of semen heat stress. After ten weeks, the sperm head recovered its normal shape. Unshorn rams are better adapted to summer heat stress than shorn ones. Microscopy and transmission electron microscopy alterations have been shown to be excellent indicators of thermal stress in Australian Merino rams and may be useful tools to help sheep farmers choose when to begin the mating season, which will vary depending on the environmental conditions of the summer.(AU)

Na Patagônia Norte, os ovinos têm sua estação de acasalamento iniciada em 15 de março, portanto, ficam sujeitos às temperaturas do verão. A exposição de carneiros a estresse térmico aumenta a prevalência de danos microscópicos e anomalias morfológicas nos espermatozoides, que implica uma redução na fertilidade. Este trabalho avaliou a capacidade adaptativa de carneiros Merino Australiano com lã (N = 6) e tosquiados (N = 6): metade ficou ao ar livre e outra metade foi mantida em uma câmara climática por oito horas, durante cinco dias, chegando gradualmente a uma temperatura máxima de 40 °C. Foram analisados danos microscópicos, anormalidades e alterações ultramicroscópicas da membrana plasmática e do acrossoma da cabeça dos espermatozoides. Os resultados microscópicos confirmaram a existência de diferença significativa na porcentagem de espermatozoides sem cauda e com gota citoplasmática proximal, entre os ejaculados pós-tratamento. A temperatura afetou os carneiros tosquiados, principalmente a cabeça de seus espermatozoides, durante a espermatogênese. Alterações submicroscópicas foram observados na membrana plasmática quando ela estava presente no segmento anterior: quando não intacta, ficava ondulada ou dilatada. Quando a membrana plasmática estava ausente, o acrossoma podia se apresentar ondulado ou dilatado. Além disso, sob efeito do calor, a membrana acrossomal externa pode perder completamente seu conteúdo ou apresentar núcleo desnudo. A membrana plasmática assume uma forma ondulada pelo efeito da temperatura no epidídimo. Depois de dez semanas, a cabeça dos espermatozoides recuperou sua forma normal. Como demonstrado neste estudo, a cabeça sem cauda, as gotas citoplasmáticas proximais e as categorias ultramicroscópicas estudadas são indicadores do efeito do estresse térmico no sêmen, e os carneiros com maior cobertura de lã se adaptam melhor ao estresse por calor. Alterações de microscopia e de microscopia eletrônica de transmissão têm se mostrado excelentes indicadores de estresse por calor em carneiros Merino Australiano e podem ser ferramentas úteis para ajudar criadores de ovelhas a escolher quando começar a época de acasalamento, o que irá variar de acordo com as condições ambientais do verão.(AU)

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BACKGROUND: In Central America, chronic interstitial nephritis of agricultural communities (CINAC) has reached epidemic proportions. Clusters of cases have been described in several farming communities. Its aetiology remains uncertain and a controversy exists on its key triggers, among them the heat stress-dehydration mechanism and the toxic exposure to agrochemicals. METHODS: This study analysed the mortality pattern and trend of chronic kidney disease code N18 (CKD-N18) according to the International Statistical Classification of Diseases and Related Health Problems-10th Revision, the proxy and the underlying cause of death, in four selected Central American countries from 1997 to 2013. In addition, we used exponential regression to retrospectively model the likely onset and prior trajectory of the epidemic. RESULTS: Between 1997 and 2013, CKD-N18 mortality accounting 47 885 deaths (31% were female), 19 533 of which occurred below 60 years of age (26% female). The excess of mortality starts as early as 10-14 years of age for both boys and girls. El Salvador and Nicaragua, with mortality rates between 9-fold and 12-fold higher than reference countries, were the most affected. Statistical modelling suggests that the epidemic commenced around the mid-1970s, coinciding with important changes in modes of agricultural production. CONCLUSIONS: This study provides the most comprehensive mortality analysis of this epidemic published to date and confirms an excess of CKD-N18 mortality and its relation with the epidemic of CINAC. The overall trends and the mortality pattern among women, children and adolescents suggest that the heat stress-dehydration hypothesis cannot fully explain this epidemic and that other environmental factors, more likely agricultural practices and agrochemicals, may be causally involved.

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RESUMO

Macroscopic and microscopic changes in the epiphyseal region of the tibia were recorded in the 42nd day of life of broilers subjected to one-hour heat stress in different rearing phases. The treatments comprised both broilers reared under room temperature and humidity conditions from the 1st to the 42nd day of life (control) and broilers subjected to heat stress from the 16th to the 21st, from the 22nd to the 42nd, and from the 16th to the 42nd day of life. The adopted design was completely randomized with six replicates; 35 broilers were used in each experimental unit. Fragments from the epiphyseal region were extracted and sectioned lengthwise for macro and microscopic analyses. Data on tibia lesion scores were analyzed by Kruskal Wallis test at 5%. The one-hour cyclic heat stress did not change the morphologic integrity in the epiphyseal region of the tibia in the different treatments. Broilers subjected to one-hour cyclic heat stress did not develop lesions that suggested tibial dyschondroplasia, regardless of the rearing phase.(AU)

Foram estudadas alterações macroscópicas e microscópicas na região epifisária da tíbia no 42º dia de frangos de corte submetidos ao estresse cíclico de calor por uma hora em diferentes fases de criação. Os tratamentos compreenderam aves criadas em condições naturais de temperatura e umidade relativa do primeiro ao 42º dia de idade (controle), ou estressadas por calor do 16º ao 21º dia, do 22º ao 42º dia e do 16º ao 42º dia. O delineamento utilizado foi o inteiramente casualizado com seis repetições sendo 35 aves por unidade experimental. Para análises macro e microscópicas da tíbia, fragmentos da região epifisária foram extraídos e seccionados longitudinalmente. Os dados de escores de lesões tibiais foram analisados pelo teste de Kruskall Wallis a 5%. O estresse cíclico por calor por uma hora não alterou a integridade morfológica da região epifisária da tíbia nos diferentes tratamentos. Frangos de corte submetidos por uma hora diária ao estresse de calor não desenvolvem lesões sugestivas de discondroplasia tibial independente da fase de criação.(AU)

Assuntos

RESUMO

Macroscopic and microscopic changes in the epiphyseal region of the tibia were recorded in the 42nd day of life of broilers subjected to one-hour heat stress in different rearing phases. The treatments comprised both broilers reared under room temperature and humidity conditions from the 1st to the 42nd day of life (control) and broilers subjected to heat stress from the 16th to the 21st, from the 22nd to the 42nd, and from the 16th to the 42nd day of life. The adopted design was completely randomized with six replicates; 35 broilers were used in each experimental unit. Fragments from the epiphyseal region were extracted and sectioned lengthwise for macro and microscopic analyses. Data on tibia lesion scores were analyzed by Kruskal Wallis test at 5%. The one-hour cyclic heat stress did not change the morphologic integrity in the epiphyseal region of the tibia in the different treatments. Broilers subjected to one-hour cyclic heat stress did not develop lesions that suggested tibial dyschondroplasia, regardless of the rearing phase.

Foram estudadas alterações macroscópicas e microscópicas na região epifisária da tíbia no 42º dia de frangos de corte submetidos ao estresse cíclico de calor por uma hora em diferentes fases de criação. Os tratamentos compreenderam aves criadas em condições naturais de temperatura e umidade relativa do primeiro ao 42º dia de idade (controle), ou estressadas por calor do 16º ao 21º dia, do 22º ao 42º dia e do 16º ao 42º dia. O delineamento utilizado foi o inteiramente casualizado com seis repetições sendo 35 aves por unidade experimental. Para análises macro e microscópicas da tíbia, fragmentos da região epifisária foram extraídos e seccionados longitudinalmente. Os dados de escores de lesões tibiais foram analisados pelo teste de Kruskall Wallis a 5%. O estresse cíclico por calor por uma hora não alterou a integridade morfológica da região epifisária da tíbia nos diferentes tratamentos. Frangos de corte submetidos por uma hora diária ao estresse de calor não desenvolvem lesões sugestivas de discondroplasia tibial independente da fase de criação.

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Toll-like receptors (TLRs) are well-characterized in mice and rats, but little is known on their role in broiler chickens during acute heat stress (AHS). The aim of the present study was to estimate the change in TLR4 mRNA expression in the liver, kidney's pleen, heart, and small intestine of broiler chickens under AHS. A total of 240 healthy Arbor Acres (AA) broiler chickens were randomly divided into four groups: control group (22±1°C; 0h), HS2, HS5 and HS10 (38±1°C; 2h, 5h and 10h of heat stress, respectively). As AHS duration increased, TLR4 mRNA expression slightly decreased at HS2 and HS5, but was dramatically elevated in HS10 (p 0.001) compared with the control group in the small intestine, as well as in the spleen at HS2 (p=0.001) and HS10 (p 0.001). The mRNA expression levels of TLR4 significantly increased in the liver, heart, and kidneys (p 0.001) at HS10, and in the kidneys at HS5 (p=0.003). It is found that TLR4 mRNA expression at HS10 in different organs was significantly higher (p 0.001) compared with HS2 and HS5. The results of the present study suggest that AHS may modulate the functional responses of the liver, kidney, spleen, heart, and small intestine of broilers by regulating TLR4 mRNA expression.(AU)

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RESUMO

Toll-like receptors (TLRs) are well-characterized in mice and rats, but little is known on their role in broiler chickens during acute heat stress (AHS). The aim of the present study was to estimate the change in TLR4 mRNA expression in the liver, kidney's pleen, heart, and small intestine of broiler chickens under AHS. A total of 240 healthy Arbor Acres (AA) broiler chickens were randomly divided into four groups: control group (22±1°C; 0h), HS2, HS5 and HS10 (38±1°C; 2h, 5h and 10h of heat stress, respectively). As AHS duration increased, TLR4 mRNA expression slightly decreased at HS2 and HS5, but was dramatically elevated in HS10 (p 0.001) compared with the control group in the small intestine, as well as in the spleen at HS2 (p=0.001) and HS10 (p 0.001). The mRNA expression levels of TLR4 significantly increased in the liver, heart, and kidneys (p 0.001) at HS10, and in the kidneys at HS5 (p=0.003). It is found that TLR4 mRNA expression at HS10 in different organs was significantly higher (p 0.001) compared with HS2 and HS5. The results of the present study suggest that AHS may modulate the functional responses of the liver, kidney, spleen, heart, and small intestine of broilers by regulating TLR4 mRNA expression.

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BACKGROUND: An epidemic of progressive kidney failure afflicts sugarcane workers in Central America. Repeated high-intensity work in hot environments is a possible cause. OBJECTIVES: To assess heat stress, dehydration, biomarkers of renal function and their possible associations. A secondary aim was to evaluate the prevalence of pre-shift renal damage and possible causal factors. METHODS: Sugarcane cutters (N=189, aged 18-49 years, 168 of them male) from three regions in El Salvador were examined before and after shift. Cross-shift changes in markers of dehydration and renal function were examined and associations with temperature, work time, region, and fluid intake were assessed. Pre-shift glomerular filtration rate was estimated (eGFR) from serum creatinine. RESULTS: The mean work-time was 4 (1.4-11) hours. Mean workday temperature was 34-36 °C before noon, and 39-42 °C at noon. The mean liquid intake during work was 0.8L per hour. There were statistically significant changes across shift. The mean urine specific gravity, urine osmolality and creatinine increased, and urinary pH decreased. Serum creatinine, uric acid and urea nitrogen increased, while chloride and potassium decreased. Pre-shift serum uric acid levels were remarkably high and pre-shift eGFR was reduced (<60 mL/min) in 23 male workers (14%). CONCLUSIONS: The high prevalence of reduced eGFR, and the cross-shift changes are consistent with recurrent dehydration from strenuous work in a hot and humid environment as an important causal factor. The pathophysiology may include decreased renal blood flow, high demands on tubular reabsorption, and increased levels of uric acid.

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This paper contextualizes the chronic kidney disease epidemic and related burden of disease affecting Central American farming communities. It summarizes the two main causal hypotheses (heat stress and agrochemicals), draws attention to the consequences of dichotomous reasoning concerning causality, and warns of potential conflicts of interest and their role in "manufacturing doubt." It describes some methodological errors that compromise past study findings and cautions against delaying public health actions until a conclusive understanding is reached about the epidemic's causes and underlying mechanisms. It makes the case for a comprehensive approach to the historical, social and epidemiological facts of the epidemic, for critically assessing existing studies and for enhanced rigor in new research.

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This brief review is based on a President's Lecture presented at the Annual Meeting of the American College of Sports Medicine in 2013. The purpose of this review was to assess the effects of climate change and consequent increases in environmental heat stress on the aging cardiovascular system. The earth's average global temperature is slowly but consistently increasing, and along with mean temperature changes come increases in heat wave frequency and severity. Extreme passive thermal stress resulting from prolonged elevations in ambient temperature and prolonged physical activity in hot environments creates a high demand on the left ventricle to pump blood to the skin to dissipate heat. Even healthy aging is accompanied by altered cardiovascular function, which limits the extent to which older individuals can maintain stroke volume, increase cardiac output, and increase skin blood flow when exposed to environmental extremes. In the elderly, the increased cardiovascular demand during heat waves is often fatal because of increased strain on an already compromised left ventricle. Not surprisingly, excess deaths during heat waves 1) occur predominantly in older individuals and 2) are overwhelmingly cardiovascular in origin. Increasing frequency and severity of heat waves coupled with a rapidly growing at-risk population dramatically increase the extent of future untoward health outcomes.

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Identification of parameters/metrics associated with environmental adaptation is one of the main trends and challenges for livestock worldwide. Thus, this study was conducted at Nhumirim Farm, in Nhecolândia, Pantanal, during the month of February, period with highest ambient temperatures. We used five cattle of each genetic group (White Nelore, Red Nelore and Pantaneira) to evaluate characteristics related to heat tolerance. Heart rate (HR), respiratory rate (RR), rectal temperature (RT), skin temperature (ST), sweating rate (SR), morphometric measurements, hair length (HL) and heat tolerance index (HTI) were evaluated. During the study the air temperature ranged from 29.0 to 40.0C and the average relative humidity was 75%. RT and ST were highest in White Nelore, followed by Red Nelore and Pantaneira. The average HTI value for the three groups was between 9 and 10, indicating high tolerance. The environment had considerable effect on physiological variables, except RR, RT and SR that significantly differed between genetic groups, with Nelore being higher than the Pantaneira, but all within physiological limits. Multivariate analysis showed the importance of variables such as sweating rate and hair length for the adaptation of cattle in the region. The red Nelore separated from the other two groups.

A identificação de parâmetros/ métricas associados à adaptação ambiental é uma das principais tendências e desafios da pecuária mundial. Desta forma, o objetivo deste trabalho foi avaliar as características de tolerância ao calor de bovinos da raça Nelore e Pantaneiro no ecossistema do Pantanal matogrossense no pico de calor da região. Estes animais foram mantidos por duas horas à sombra (8:00h às 10:00h) e em seguida uma hora ao sol (10:00h às 11:00h). Após a exposição foram analisados parâmetros de frequência cardíaca (FC), frequência respiratória (FR), temperatura retal (TR), temperatura superficial da costela (TSC), temperatura superficial do pescoço (TSP) e temperatura superficial da garupa (TSG). Também foram avaliados a taxa de sudação (TXS), comprimento e densidade de pelos e calculados o índice de tolerância ao calor (ITC). No período estudado, a temperatura ambiental variou de 29,0 a 40,0C e a média para umidade relativa foi de 75%. O ambiente teve influência marcante sobre as variáveis fisiológicas, com exceção da FR. A TR e a TXS diferiram significativamente entre os grupos genéticos, sendo da raça Nelore mais elevada em relação à Pantaneira, mas todas dentro dos limites fisiológicos. A análise multivariada mostrou a importância de variáveis como taxa de sudação e comprimento de pelos para adaptação de bovinos na região.

Assuntos

RESUMO

Identification of parameters/metrics associated with environmental adaptation is one of the main trends and challenges for livestock worldwide. Thus, this study was conducted at Nhumirim Farm, in Nhecolândia, Pantanal, during the month of February, period with highest ambient temperatures. We used five cattle of each genetic group (White Nelore, Red Nelore and Pantaneira) to evaluate characteristics related to heat tolerance. Heart rate (HR), respiratory rate (RR), rectal temperature (RT), skin temperature (ST), sweating rate (SR), morphometric measurements, hair length (HL) and heat tolerance index (HTI) were evaluated. During the study the air temperature ranged from 29.0 to 40.0C and the average relative humidity was 75%. RT and ST were highest in White Nelore, followed by Red Nelore and Pantaneira. The average HTI value for the three groups was between 9 and 10, indicating high tolerance. The environment had considerable effect on physiological variables, except RR, RT and SR that significantly differed between genetic groups, with Nelore being higher than the Pantaneira, but all within physiological limits. Multivariate analysis showed the importance of variables such as sweating rate and hair length for the adaptation of cattle in the region. The red Nelore separated from the other two groups.(AU)

A identificação de parâmetros/ métricas associados à adaptação ambiental é uma das principais tendências e desafios da pecuária mundial. Desta forma, o objetivo deste trabalho foi avaliar as características de tolerância ao calor de bovinos da raça Nelore e Pantaneiro no ecossistema do Pantanal matogrossense no pico de calor da região. Estes animais foram mantidos por duas horas à sombra (8:00h às 10:00h) e em seguida uma hora ao sol (10:00h às 11:00h). Após a exposição foram analisados parâmetros de frequência cardíaca (FC), frequência respiratória (FR), temperatura retal (TR), temperatura superficial da costela (TSC), temperatura superficial do pescoço (TSP) e temperatura superficial da garupa (TSG). Também foram avaliados a taxa de sudação (TXS), comprimento e densidade de pelos e calculados o índice de tolerância ao calor (ITC). No período estudado, a temperatura ambiental variou de 29,0 a 40,0C e a média para umidade relativa foi de 75%. O ambiente teve influência marcante sobre as variáveis fisiológicas, com exceção da FR. A TR e a TXS diferiram significativamente entre os grupos genéticos, sendo da raça Nelore mais elevada em relação à Pantaneira, mas todas dentro dos limites fisiológicos. A análise multivariada mostrou a importância de variáveis como taxa de sudação e comprimento de pelos para adaptação de bovinos na região.(AU)

Assuntos

RESUMO

O estresse por calor, comum em clima tropical, vem sendo considerado um dos principais fatores de falha reprodutiva de fêmeas bovinas, incluindo danos ao desenvolvimento e maturação oocitária, desenvolvimento embrionário inicial e fetal, lactação e endocrinologia reprodutiva. Para tentar minimizar tais prejuízos, é necessário melhor entendimento da influência térmica sobre os processos reprodutivos a fim de aperfeiçoar o manejo para aumentar a fertilidade. Esta revisão tem como objetivo buscar o melhor entendimento de como e quando o estresse por calor afeta a reprodução de bovinos, no intuito de se desenvolver estratégias visando melhorar a fertilidade em ambientes de elevadas temperatura.

The heat stress, common in tropical climates, has been considered one of the major factor in reproductive failure in cows, including damages in the oocyte development and maturations, early embryo and fetus development, lactations and reproductive endocrinology. The genetic adaptation to heat stress is possible not only in relation to the body temperature regulation, but also at cellular resistance level. To try to minimize these problems, a better understanding of the thermal influence on the reproductive processes is necessary, with the aim of improving the reproductive management. This review aims to offer a better understanding of how and when the heat stress affects reproductive function of bovines, in order to develop strategies to increase fertility in environments with high thermal loads.

El estrés por calor, común en climas tropicales, ha sido considerado uno de los principales factores de fracaso reproductivo en hembras bovinas, incluyendo daños al desarrollo y maduración oocitaria, desarrollo embrionario inicial y fetal, lactancia y endocrinología reproductiva. Para intentar minimizar estos problemas, es necesario entender mejor la influencia térmica en los procesos reproductivos, con el fin de perfeccionar el manejo para aumentar la fertilidad. Esta revisión tiene como objetivo buscar mejor comprensión de cómo y cuándo el estrés por calor afecta la reproducción del ganado, buscando desarrollar estrategias para mejorar la fertilidad en entornos de elevadas temperatura.

Assuntos

RESUMO

O estresse por calor, comum em clima tropical, vem sendo considerado um dos principais fatores de falha reprodutiva de fêmeas bovinas, incluindo danos ao desenvolvimento e maturação oocitária, desenvolvimento embrionário inicial e fetal, lactação e endocrinologia reprodutiva. Para tentar minimizar tais prejuízos, é necessário melhor entendimento da influência térmica sobre os processos reprodutivos a fim de aperfeiçoar o manejo para aumentar a fertilidade. Esta revisão tem como objetivo buscar o melhor entendimento de como e quando o estresse por calor afeta a reprodução de bovinos, no intuito de se desenvolver estratégias visando melhorar a fertilidade em ambientes de elevadas temperatura.(AU)

The heat stress, common in tropical climates, has been considered one of the major factor in reproductive failure in cows, including damages in the oocyte development and maturations, early embryo and fetus development, lactations and reproductive endocrinology. The genetic adaptation to heat stress is possible not only in relation to the body temperature regulation, but also at cellular resistance level. To try to minimize these problems, a better understanding of the thermal influence on the reproductive processes is necessary, with the aim of improving the reproductive management. This review aims to offer a better understanding of how and when the heat stress affects reproductive function of bovines, in order to develop strategies to increase fertility in environments with high thermal loads.(AU)

El estrés por calor, común en climas tropicales, ha sido considerado uno de los principales factores de fracaso reproductivo en hembras bovinas, incluyendo daños al desarrollo y maduración oocitaria, desarrollo embrionario inicial y fetal, lactancia y endocrinología reproductiva. Para intentar minimizar estos problemas, es necesario entender mejor la influencia térmica en los procesos reproductivos, con el fin de perfeccionar el manejo para aumentar la fertilidad. Esta revisión tiene como objetivo buscar mejor comprensión de cómo y cuándo el estrés por calor afecta la reproducción del ganado, buscando desarrollar estrategias para mejorar la fertilidad en entornos de elevadas temperatura.(AU)

Assuntos

RESUMO

Much of the effect of heat stress on establishment and maintenance of pregnancy involves changes in ovarian function and embryonic development that reduce the competence of the oocyte to be fertilized and the resultant embryo to develop. There are three possible therapeutic approaches to manipulate the connection between hyperthermia and cellular responses to elevated temperature to improve fertility during heat stress. Embryo transfer is based on the idea that 1) most effects of heat stress on fertility involve actions during folliculogenesis or on cleavagestage embryos and 2) the embryo has acquired resistance to elevated temperature by the time it is transferred at t he morula or blastocyst stage. The mechanisms for acquis ition of thermotolerance involve changes in production of reactive oxygen species in response to heat shock as well as accumulation of antioxidants in the embryo. Synthesis of heat shock proteins may not be the controlling factor for acq uisition of thermotolerance because transcript abundance for HSPA1A and HSP90AA1 is higher for the two-cell embryo than morula. Involvement of reactive oxygen species in actions of elevated temperature on embryo survival is indicative that provision of ant ioxidants to heat-stressed cows could improve fertility. More work is needed but there are indications that pregnancy rates can be improved by feeding supplemental β-carotene or administration of melatonin implants. It is also evident that there are genes that control thermoto lerance at the cellular level. Brahman, Nelore and Romosinuano embryos have increased resistance to heat shock as compared to Holstein or Angus embryos. Mutations in the gene for heat shock protein 70 that control resistance of cells t o heat shock have been identified in Holsteins. Selection for the desirable alleles of genes conferring cellular thermotolerance could lead to development of strains of cattle whose fertility is resistant to disruption by heat stress. Pursuing these and other therapeutic approaches for reducing consequences of heat stress for livestock species should be a priority because of the prospects for continuing global climate change.(AU)

Assuntos

RESUMO

Infertility has been linked to numerous factors in high producing dairy cattle in the last decades. The detection of estrus continues to present difficulties and, although progress has been made in regards to estrus synchronization and artificial insemination, the reproductive performance of dairy cows has not improved substantially. Moreover, in warm countries, summer heat stress is a major factor impairing fertility. This presentation expresses our views on factors of a non infectious nature that affect the fertility of lactating dairy cows following AI. Special attention is paid to factors related to the cow and its environment and to some approaches to increase reproductive efficiency such as confirmation of estrus at insemination and the insemination procedure.(AU)

Assuntos