Adaptative Responses of Brazilian Brahman Bulls in Different Seasons Débora Andréa Evangelista Façanha 1 ; Wirton Peixoto Costa 1 ; Paula Priscilla Liberato da Escóssia Campos 2 ; Jacinara Hody Gurgel Morais Leite 2 ; Aldo Silva Valente Junior 3 ; Thiago Camargo Vieira 3 ; Luis Alberto Bermejo Asensio 4 ; José Ernandes Rufino da Silva 1 1. Department of Animal Science Universidade Federal Rural do Semiárido 2. Post Graduation Studant in Animal Science Universidade Federal Rural do Semiárido 3. Uberbrahman Group (Frutab Agricola S/A) Uberlandia/MG - Brazil 4. Universidad de La Laguna Tenerife - ES Introduction Environmental high temperatures are detrimental to the productivity of livestock industry, because animals of better genotype normally have a higher endogenous heat, due to their metabolic activity. Heat stress is one of the most important factors that affect animals performance in tropical regions, specially beef cattle managed in extensive field conditions. With the aim to develop efficient livestock systems the search for heat tolerant genotypes is increasing in the last years, in brazilian tropical regions, becouse of their ability to adjustments to climatic changes. The capacity of the animals to maintain the equilibrium with thermal environment is directly associated with their ability to trigger thermoregulatory mechanisms, which depends on a pool of morphological and physiological traits acquired during the evolutionary process, in order to guarantee the efficiency of thermoregulation. Brahmans cattle have strong skin pigmentation, which filters the intense short wave radiation as well as keeps the breed free of cancer. A special feature of the Brahman breed is their ability over other breeds to sweat freely, which contributes greatly to their heat tolerance. Other adaptative advantages which make the Brahman well suited to many environmentals conditions include the ability to utilize lower-quality food, to travel longer distances for feed and water, to resist insects and external parasites and also the ability to reproduce on a regular basis in a stressful environment. A factor which contributes to the Brahman's unique ability to withstand temperature extremes is a short, thick, glossy hair coat which reflects much of the sun's rays, allowing them to graze in midday sun without suffering.
The goal of this work was to evaluate the adaptative responses of young Brahman Bulls in Cerrado bioma, based in thermoregulatory, morfophysiololic and blood biochemistry parameters, during the dry and wet seasons. Material and Methods The study was performed in a commercial farm located in Uberlândia-MG, Brazil, at 18 55 S, in the Cerrado Bioma. Were used 63 young Brahman bulls, aging about 233 to 264 days. The trial was iniciated at the weaning and the evaluations were conducted for seven months, involving dry and wet season. Sampling were conducted once a month and the data were collected once a day, from the 8:00 AM to 11:00 AM, under natural field conditions. The environmental traits registered consisted in wind speed (WS, m/s), air temperature (AT, C), wet bulb temperature (WBT, C) and black globe temperature (BGT, C), utilized to estimate the radiant heat load (RHL, W/m²) and Black Globe Humidity Index (BGHI). These variables were registered at the same time of data collect in the animals. Respect to thermoregulatory profile the bulls were evaluated for rectal temperature (RT, C); respiratory rate (RR, breaths for minute) and sweating rate (g/cm 2 /min). Blood parameters were evaluated in the first collect, at the middle of the trial and in the last collect. The analysis consisted in hematologic traits (white and red blood cells and platelets), thyroid hormones as Triiodothyronin (T 3 ) and Thyroxin (T 4 ), and Cortisol concentrations. The morphologic evaluations consisted in hair coat density (CD, hair/cm2); coat thikness (CT, mm), hair lenght (HL, mm) and mean hair diameter (HD, mm); To test our hyphotesis, were considered as fixed effects the collect and the animals. The Principal Component Analysis was used to evaluate the principal characteristics that can be used to describe the adaptative profile of the breed under Brazilian Cerrado conditions. Results and Discussion In the Table 1 can be observed the significative effect of the month of sampling on environmental characteristics, showing that January was the most stressful month, according to the higher mean of radiant heat load. The rainfall period was from November to march, in summer season, when were registered the most elevated means of air humidity. Table 1. Environmental traits and physiological responses of Brazilian Brahman young bulls in a tropical environment. Sampling RH (%) RHL(W/m 2 ) RT ( C) RR(b/min) SR(W/m 2 /s) September 38,81 d 453,41 cd 38,83 abc 31,68 a 1714,07 a November 59,67 b 443,90 d 38,73 bc 25,04 dc 1632,40 ab December 60,78 b 471,65 b 39,15 ab 23,53 dc 1250,61 c January 71,69 a 501,35 a 39,29 a 30,22 ba 1319,93 c March 63,84 b 481,35 b 38,91 abc 25,49 dc 1295,07 c June 38,81 d 455,24 bc 38,85 abc 27,65 bc 1445,42 bc August 54,38 c 443,37 d 38,44 c 21,14 e 1572,51 ab X 53,43 464,32 38,89 26,39 1460,51 R 2 0,74 0,35 0,37 0,54 0,57 CV 15,97 5,45 2,05 18,15 27,7 Means followed by the same letters in the rows did not different, by Tukey test at 5%. AT: Air temperature; RT: Relative humidity; RHL: Radiant heat load; RT: Rectal temperature; RR: Respiratory rate; SR: Sweating rate
The associated effects of high air humidity and high solar radiation can result in a more stressful environment, so in this period the animals must receive an special attention to cope with the thermal stress. Respect to thermoregulatory patterns we verified that in December and January the animals exhibited the highest values of rectal and skin surface temperature, followed by the highest means of respiratory rate and sweating rate, as shown in Table 1. These results indicated the use of cutaneous and respiratory evaporative losses as an efficient way to dissipate the excessive heat, once a time that in this period were registered the highest environmental radiant heat load, associated to high air humidity. Nevertheless, the normal values of rectal temperature confirmed the homeothermic condition reached for the animals in all the seasons evaluated. In the Table 2 can be observed that the hair diameter exhibited a very small variation along the year. The coat thickness was higher during the most cold period and this can promote a more efficient thermal protection, once a time that the animals can keep the air near the skin surface and be protected from the excessive heat losses. Table 2. Coat characteristics of Brazilian Braman youg bulls, during the year, in a tropical environment. Sampling Coat Thickness (cm) Coat Density (hair/cm 2 ) Hair Diameter ( m) Hair Lenght (mm) September 0,208 d 1397,7 b 0,0276 b 8,78 c November 0,304 bc 1644,5 b 0,0368 a 9,24 c December 0,309 bc 2088,5 a 0,0369 a 8,85 c January 0,271 c 1958,3 ab 0,0367 a 8,89 c March 0,323 b 1336,6 b 0,0384 a 10,83 b June 0,330 ab 1851,5 ab 0,0380 a 11,03 b August 0,370 a 1829,5 ab 0,0378 a 15,04 a X 0,301 1728,82 0,036 10,36 R 2 0,68 0,531 0,400 0,673 CV 34,82 48,63 17,46 18,42 Means followed by the same letters in the rows did not different, by Tukey test at 5%. The coat density was higher during the summer (December January) and the winter (June August), then decreased during spring (September November) and the autumn (March). These findings can explain the change of the longer hairs registered in colder months (March August) which were substituted by the short fibers verified during the hottest period (December January). This results are in agreement with some studies conducted in tropical Brazilian regions and shows the important role that the hair coat characteristics plays in adaptation to the climatic conditions. In the Table 3 can be observed that all the blood parameters, such as hematologic and thyroid hormones concentrations were compatible with the normal range along the year, confirming the health and the homeostatic condition. The immunity function, as indicated by the platelets account, was kept inside the normal range and this result can confirm the adaptation, once a time that the animals can trigger normally the organic defence mechanisms and be free of diseases, under the environmental conditions evaluated.
Table 3. Hematological and Hormonal responses of Brazilian Brahman young bulls in a tropical environment. Sampling Inicial (September) Middle (January) Final (August) General Means Standard Deviation Red Blood Cells 10,50 a 8,16 b 8,01 b 1,510 2,28 (mil/mm 3 ) Hematocrit (%) 35,60 a 29,18 b 28,64 b 4,293 18,43 Corpuscular Mean 34,02 b 35,90 a 35,45 a 36,19 3,76 Volume ( fm 3 ) White Blood cells (mil/ mm 3 ) 13026,92 a 11737,70 b 13,961,29 a 13119,29 3217,95 Platelets(mil/ mm 3 ) 403230,77 b 553934,43 a 352241,94 b 418504,82 159241,59 Triiodothyronin 3,03 b 2,93 b 3,81 a 3,31 1,13 ( g/dl) Thyroxin ( g/dl)* 235,04 a 144,03 b 239,43 a 193,31 134,42 Cortisol ( g/dl) 60,83 b 91,31 a 40,47 c 63,27 49,22 Means followed by the same letters in the column, did not different, by Tukey test at 5%. * Total Thyroxin The serum concentrations of Triiodothyronin were lower in September and January, while the Thyroxin concentration dropped only in January. These results may be due to the hottest condition verified during the summer, which can induce the reduction of Thyroid activity, aiming to reduce the endogenous heat production. The more stressful thermal condition was accompanied by the higher concentrations of cortisol, an unspecific but important indicator of environmental stress. Principal Component Analysis (PCA) of physiological and morphological variables average showed that respiratory rate, sweating rate, coat thickness and hair length are the most relevant variables of bull distribution in axis 1 (29,8% of explained variance) and coat thickness, hair length and mean hair diameter in axes 2 (17% of explained variance). Therefore, bulls that showed high coat thickness and hair length used respiratory rate instead of sweating in order to maintain normal body temperature as axis 1 showed. Less relevant is the fact that some bulls characterized by high hair length, mean diameter and coat thickness did not modify physiological variables (as show axis 2). According to PCA results, most relevant variables were used to k-means clustering analysis. Bulls were classified in three groups basing on PCA most relevant variables (coat thickness, heat load, mean diameter, respiratory rate and sweating rate): high (n = 39), mean (n = 11) and low adaptive capacity (n = 12). The high adaptive considered group showed lower CT, HL, RR and SR. Additionally, PCA of physiological and morphological variables standard deviation showed that bulls distribution depends on uneven level response of respiratory rate, sweating rate and hair diameter, as axis 1 showed (22,8% of explained variance). PCA axis 1 point out that those animals that tend to maintain mean diameter among samples showed uneven evaporative thermolysis, indicated by lower respiratory and sweeping rate. Among animals characterized by stable respiratory and sweating rate (low value of PCA axis 1), PCA axis 2 shows that animals tend to maintain body temperature when are characterized by uneven hair length and coat thickness among samples. The animals who exhibited higher phenotypical plasticity for hair coat traits were able to keep normal and stable physiologic responses.
Conclusion We concluded that Brahman cattle exhibited morfophysiological traits that promotes the homeothermy and the adaptation under Brazilian cerrado conditions. For that reason this breed can be indicated to meat production in extensive system, however special attention must be done to heat stress management during the hottest and humid months, once a time that heat stress reactions increased even in more adapted animals. Acknowledgement The authors acknowledge the Uberbrahman Group, specially Dr. Thiago Camargo and Dr. Aldo Valente, that supported the present study.