The aim of the present study was to assess the heat tolerance of animals of two Portuguese (Alentejana and Mertolenga) and two exotic (Frisian and Limousine) cattle breeds, through the monitoring of physiological acclimatization reactions in different thermal situations characterized by alternate periods of thermoneutrality and heat stress simulated in climatic chambers. In the experiment, six heifers of the Alentejana, Frisian and Mertolenga breeds and four heifers of the Limousine breed were used. The increase in chamber temperatures had different consequences on the animals of each breed. When submitted to heat stress, the Frisian animals developed high thermal polypnea (more than 105 breath movements per minute), which did not prevent an increase in the rectal temperature (from 38.7 degrees C to 40.0 degrees C). However, only a slight depression in food intake and in blood thyroid hormone concentrations was observed under thermal stressful conditions. Under the thermal stressful conditions, Limousine animals decreased food intake by 11.4% and blood triiodothyronine (T3) hormone concentration decreased to 76% of the level observed in thermoneutral conditions. Alentejana animals had similar reactions. The Mertolenga cattle exhibited the highest capacity for maintaining homeothermy: under heat stressful conditions, the mean thermal polypnea increased twofold, but mean rectal temperature did not increase. Mean food intake decreased by only 2% and mean T3 blood concentration was lowered to 85,6% of the concentration observed under thermoneutral conditions. These results lead to the conclusion that the Frisian animals had more difficulty in tolerating high temperatures, the Limousine and Alentejana ones had an intermediate difficulty, and the Mertolenga animals were by far the most heat tolerant.

RESUMO -Este trabalho foi realizado, no verão de 2002, com o objetivo de avaliar a influência de alguns recursos de climatização na produção de leite e na termorregulação dos animais. Foram utilizadas 10 primíparas e 17 multíparas em lactação, distribuídas em instalação controle (ICO), instalação com nebulizador associado a ventiladores (ICL) e instalação com tela de sombreamento (IT). A produção de leite e o consumo individual foram medidos diariamente para cada animal. A temperatura retal foi medida três vezes ao dia, em três animais de cada instalação; a temperatura de superfície da pele, três vezes ao dia em todos os animais; e a freqüência respiratória, duas vezes ao dia em todos os animais. Os dados climáticos de cada instalação foram registrados e posteriormente calculados os índices de temperatura e umidade (ITU) e de globo negro e umidade (ITGU). Foram selecionados e analisados 26 dias com entalpia elevada. O ITU entre 75 e 76, apesar de considerado estressante por diversas fontes da literatura, não foi associado à condição de estresse pelos animais. As multíparas da instalação climatizada apresentaram freqüência respiratória e temperatura de pele significativamente menor em relação às multíparas das demais instalações. As primíparas apresentaram freqüências respiratórias e temperaturas retais mais altas que as multíparas, nos horários mais quentes do dia. A maior produção de leite das multíparas foi observada no tratamento com tela.Palavras-chave: estresse térmico, produção de leite, sistema de nebulização, temperatura retal, termorregulação Physiologic and Performance Responses of Holstein Cows in Milking under Different EnvironmentsABSTRACT -This work was carried out during the summer of 2002 to evaluate the influence of some cooling systems on the milk yield and animal thermoregulation. Ten heifers and seventeen milking cows were assigned to the control housing (ICO), mist & fan housing (ICL) and shade cloth (80%) (IT). The milk yield and the individual intake were daily measured for each animal. The rectal temperature was measured three times a day with three animals from each treatment. The skin surface temperature was collected three times a day for all the animals and the respiratory frequency two times a day for all the animals. The climatic data of each housing were registered to calculate the temperature humidity index (ITU) and the black globe humidity index (ITGU). Twenty six days of high enthalpy were selected and analyzed. The study showed that temperature humidity index from 75 to 76 was not associated with stress conditions for the animals, although many researches propose this situation as stressing. The milking cows in the mist & fan treatment showed respiratory frequency and skin surface temperature significantly lower than the cows in the other treatments. The heifers presented respiratory frequency and rectal temperature higher than the cows in all the registration times. The higher milk yield of the cows was observed in the shade cloth treatment.Key Words: heat stress, milk produc...

a b s t r a c tThis study's main goal was to evaluate the thermoregulatory responses velocity through the variation of rectal temperature (RT), related to the thermolytic pathways, respiratory rate (RR) and sweating rate (SR) among different sheep breeds. Ninety female sheep, eighteen of each breed: Santa Ines and Morada Nova (Brazilian hair breeds), Texel, Suffolk and Ile de France (wool breeds) were challenged during three non-consecutive summer days (22• 42 S, 47• 18 W, and 570 m of altitude, maximum air temperature of 33.5• C, average relative humidity of 52 ± 6.9%). The physiological variables were registered at 0800 h (T1), 1300 h (T2: after 2 h of shade rest), 1400 h (T3) (after one hour of sun exposure) and in the shade at 1415 h (T4), 1430 h (T5), 1445 h (T6) and 1500 h (T7) and a thermotolerance index (TCI) was calculated as (10-(T7 to T4)-T1). The statistical analysis was performed by a mathematical model including the fixed effects of breeds and time frames, and the interaction between these effects, besides random effects such as animal and day. The Santa Ines breed presented the lowest RT after sun exposure (39.3 ± 0.12• C; P < 0.05) and it was the only one to recover morning RT 60 min after heat stress (38.7 and 38.9 for 1300 h and 1500 h; P > 0.05). Hair breeds presented RR lower (P < 0.05) than wool breeds. Although thick wool or hair thickness differs among and within hair and wool breeds (P < 0.05), SR did not differ among breeds and time (227.7 ± 16.44 g m −2 h −1 ; P > 0.05). The thermotolerance index did not differ among breeds, but it showed similar response (P > 0.05) 45 min or 1 h of shade after sun exposure. One week post shearing is not enough to wool breeds present to show thermotolerance similar to hair breeds.

The objectives were to assess the degree of thermolysis capacity as a characteristic of heat tolerance of the Simmental beef cattle and evaluate the effects of shade and shade type (artificial: AS, trees: TS, or no shade: NS) on daily behavior patterns during summer. Black globe temperature (BGT) was different under the two types of shade (P < 0.05) and was lower under the TS (P < 0.01) and under AS (P > 0.01) than average BGT in the sun. Animals when in AS used more intensely the shade (P = 0.002) mostly lying down under it (10.00-14.00 hours), while time standing was similar (P = 0.107) between TS and NS. Bulls without shade (NS) spent significantly more time at the water trough and most part of the day standing idle (72.4%, 10.1 h/14 h). TS bulls spent more time grazing/standing (P < 0.001). The Simmental bulls that were in TS and AS spent more time ruminating than bulls that stay without shade (NS). The availability of shade changes grazing, rumination and idling behavior of cattle in response to environmental conditions. Shade provided by trees can be more efficient than artificial shading as cattle spent more time grazing when tree shade was available. Thermolysis capacity can be used to select heat-tolerant animals.

RESUMO -Avaliou-se o desempenho de tourinhos ¾ Europeu ¼ Zebu, de raça paterna Britânica ou Continental em dietas de alto teor de concentrado contendo 9, 15 e 21% da matéria seca (MS) de bagaço in natura (BIN) em arranjo fatorial 2x3. Trinta e seis tourinhos com idade média de 9 meses e peso vivo inicial de 257 kg foram confinados, dois por baia, por 139 dias. Não houve efeitos da interação entre tipos raciais e níveis de fibra para nenhuma variáveil analisada. Entre os dois tipos genéticos não houve diferenças em ganho de peso vivo em jejum (PVj), ABSTRACT -The objective of this work was to evaluate the performance of ¾ European x ¼ Zebu crossbred bulls of British or Continental paternal breed, fed high concentrate diets containing 9, 15 or 21% of the dry matter (DM) with sugarcane bagasse (BIN) in a 2 x 3 factorial arrangement. Thirty-six crossbred bulls, 9 months old and 257 kg of shrink body weight were fed, two per pen, for 139 days. There was no difference in shrink body weight gain between the two genetic groups, the British animals gaining 1.24 kg/d and the Continentals 1.29 kg/d. The efficiency of feed conversion was also the same, 0.17. The 15% BIN animals showed higher rates of gain (1.36 kg/d) than the 9% BIN animals (1.20 kg/d). The final weight of the British animals (428.1 kg) did not differ from the Continental bulls (438.4 kg) as well as the dry matter intake (respectively 7.20; 7.54 kg/d). Among the three roughage levels, the highest final weight was for the 15% BIN animals (448.7 kg), the lowest for the 21% BIN(424.8 kg). The highest dry matter intake was for the 15% BIN treatment (7.93 kg DM/d) and the lowest for the 9% BIN (6.85 kg DM/d). These results suggest that high concentrate diets with levels as low as 9% of BIN can be used.Key Words: bulls, feedlot, fiber, high concentrate, sugarcane bagasse, roughage R. Bras. Zootec., v.31, n.1, p.444-450, 2002 (suplemento) IntroduçãoAvaliações de diferentes grupos genéticos quanto ao desempenho, à composição corporal e às exigên-cias nutricionais são fundamentais para a elaboração de padrões de alimentação e modelos de computador que auxiliem produtores e extensionistas a conduzirem programas nutricionais no Brasil. Diversos trabalhos vêm sendo conduzidos em um amplo estudo da composição corporal de bovinos para estimar suas exigências nutricionais e eficiência de crescimento (Leme et al