The environment has a direct influence on animal performance, so as to interfere positively or negatively, depending on the level of comfort or stress, respectively, promoted by him. Thus, reproductive functions, growth, food consumption, water consumption, and also the physiological parameters (rectal temperature, respiratory rate, among others) are affected negatively in environmental conditions over the area of the thermal neutral (26-28 ° C room temperature), and therefore, any living being an environmentally result in living a modification factor that environment and at the same time, an environmental factor for all other beings of this species and other species (SILVA, 2000 ). Thus, according Baêta and Souza (1997) the external environment includes all physical, chemical, biological, social and climatic factors which interact with the animal, produces reactions in the behavior of these, thus defining the type of environment-animal relationship . Thus, the animal-port as a thermodynamic system that continuously exchanges energy with the environment. In this process, external environmental factors tend to produce internal variations in animal, influencing the amount of energy exchanged between them, there is however the need of physiological adjustments to the occurrence of heat balance. According Kunningham (2004) in situations of hot environments (stressful), animals trigger its thermoregulatory mechanism to dissipate heat from your body and, thus, maintain their body temperature within the optimum values for each species and the average rectal temperature dairy cattle equal to 38.6 ° C, accepting a limit of variation from 38 to 39.3 ° C. Therefore, it is necessary that, among other mechanisms, sweating and breathing rate are high from the time when the temperature exceeds 26-28 ° C values was also verified in situations of thermal stress, a change in animal behavior so that it increases its water consumption decreases food intake and rumination and according to Rossarola (2007), looks for shadows in the hottest hours of the day. The aim of this study was to evaluate the climatic effects on the physiological responses of dairy cows in high temperature environments.
Evaluation of Physiological Parameters Based on Governing Literature as per conducted a survey of 15 dairy cows, five of them representatives of each genetic group: 1/2, 3/4, and 7/8 Holstein-Zebu (HZ) for two years, assessing summer and winter every year . in the Experimental Field of Embrapa Dairy Cattle in Coronel Pacheco – MG Animals during the summer remained in paddocks provided natural shade and water fountains, being collected only for two milkings of the day, which occurred at 05 h 30 min. and 13 h: 30 min. However, during the winter the animals were stabled during the day, where they received forage and concentrate, being released to the pickets only at night. Rectal temperature (TR ° C), respiratory rate (RR, mov / min.) And surface temperature (TS, ° C) were evaluated at 08:00 and 14: 00h, three times a week, always after each milking and climatological variables were assessed every hour from 08:00 to 16: 00h, in a thermometer shelter ( dry bulb temperature – TBS -; wet bulb temperature – TBU – and maximum and minimum temperatures), being, however, the black globe temperature – TGN – measured at 1.7 m above ground level, next external environment to that shelter. All observations ever taken place on the date of assessment of physiological parameters. For a better understanding by producers on the variables and indices of thermal comfort, it is necessary to say: TBS is the air temperature; the TGN is the combined effect of air temperature, solar radiation and wind speed; the temperature and humidity index (THI), includes the combined effects of ambient temperature and relative humidity, the TBU is used only in conjunction with TBS to determine, through specific table, the relative humidity (RH) . Thus, the observation of these variables and the index presented here (ITU), as well as other variables and indices, provides the producer a sense of environmental windchill that their animals are subjected, is therefore important for decision-making which refers to provide better environmental conditions thereto. In figure 1 we can see that the late shift in the summer season showed the highest both the TBS TGN as compared to the morning shift is in summer or winter. We also found that the highest values were approximately 37 and 30 ° C for the TGN and TBS (summer), respectively, according to the author indicates a situation of stress from moderate to average for the studied animals. The data also reveal and this is confirmed by other literature, the afternoon shift, especially in dry seasons, gives greater condition of heat stress to the animals that the morning shift, regardless of the time of year.
Average of TBS (° C) and TGn (° C) according to the schedule (morning and afternoon) and the seasons of the year (summer and winter).
TBS = dry bulb temperature (° C).
TGN = Temperature . black globe (° C)
Dairy cows under heat stress.
The TS animals of the three genetic groups had the same behavior of other physiological parameters presented in this paper, ie increased due to the increase of UTI units (Figure 5), not realizing the figure, any change to the researched genetic groups (½, 3/4 and 7/8 Hz), although the authors reported that TS animal ½ HZ has been slightly higher than the TS of the animals from the other groups, and attributed this difference to the fact that ½ Hz animals presenting a darker tint coat, thus suggesting the possibility of higher heat absorption surface dark fur animals, compared to lighter coats of animals.
Dairy cows under the shade of trees (natural shade)
protected Dairy cows of solar radiation on the premises (artificial shade).
Final considerations and recommendations Milk production facing various production difficulties is faced with one more factor to be administered, the environment, so that farmers and researchers have a responsibility to find a balance between the various factors environmental and efficient milk production. It is evident the need of providing shading in pastures, whether natural or artificial, as well as the choice of material of the plants to absorb and reflect the smaller and larger, respectively, possible amount of solar radiation. Although the shading in the pasture does not allow full coverage of the area, which would be unworkable and undesirable, by interference in the development of it (photosynthesis), it is evident the use of shade as body cooling option by animals during the warmer periods the day, especially during hot and dry periods of the year. The observation of animal behavior in the pasture and on the premises, sets an important factor because it allows the producer to evaluate through the respiratory rate, based on the period in which it remains altered, a condition of the stress level of these animals and from then take the necessary measures to alleviate such stress. Do not forget to consider the requirements of thermal comfort of pure animals or high-derived blood level of temperate climate, in regions where the climate does not favor a thermal comfort necessary for good growth performance of these, without conducting creating environmental improvements, such as the provision of shadows and the use of proper management to the specific climatic conditions of Dubai UAE region
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