(by Veterinary Doctor Vasco Reis)
The thermal energy present in the body of an homeothermic animal (with constant temperature), is mostly generated by metabolic processes (of muscle contraction in the exercise and others) and the rest is coming from the environment, by means of radiation (solar and others).
When the environment temperature rises above 29° C, the most efficient heat loss is by evaporation (perspiration and breathing), being responsible, for example, in cattle to 85% of the heat loss. This type of loss is dependent on the relative humidity of the air.
The physical mechanism of thermolysis (to avoid overheating and to keep body temperature constant) is due mainly to evaporation.
However, in very humid environments, evaporation may become very slow.
If the region is humid (Azores), evaporative heat loss will be difficult, providing a high caloric stress.
The loss of heat by evaporation through the sweat glands is one of the mechanisms of adaptation to caloric stress in cattle, sheep, horses, goats and buffaloes.
When an animal is subjected to high temperatures, there is an increased blood flow to the skin, providing an additional amount to the sweat glands and that stimulates its action (perspiration).
Respiratory evaporation has been pointed as the main mechanism of thermolysis (to avoid overheating and to keep body temperature constant).
The respiratory rate increases when respiratory evaporative heat loss is needed for example by exercise.
Dehydration is the lack of water in the body caused by lack of fluid intake or excessive losses without replacement (sweating, breathing, diarrhea, sunstroke, ...).
The transport of nutrients and removal of waste from the body organs are made by blood (essentially consisting of water) within the blood vessels.
The decrease of blood volume decreases transportation, causes the fall of blood pressure leading to a shock (lack of blood in all organs). If there are sharp losses (diarrhea) it worsens the situation because of the loss of mineral salts (electrolytes).
This causes a strong general organism disorder, accompanied by great suffering, which can lead to death.
The same applies to bovines, before and after of bullfighting, inclusive in bullfighting with the rope (tourada à corda, corrida à corda - Azores), standing hours under the Sun inside cages without water, before and after the intense run.
This has led to many deaths, which are hidden by the fans.
It is just one more step of suffering to which animals are subjected in bullfighting.
It should be investigated and reported.