No, it´s not a horse which has to be protected from the sun or anything...A hooded horse is not, I agree, a very common site, but I will explain asap what´s this all about. Well, this animal is just doing his part in an extremely popular event, called the Cavalhadas, which takes place every year since the 17th century in a small colonial town of the state of Goiás, Pirenópolis.
Count 40 days after Easter and you´ll see hundreds of horsemen riding across this small town, many of them wearing masks and hoods as well as disguising their horses with funny-looking costumes. These guys are known as the Mascarados ( Mascarades) and their presence are never discreet. They shout, laugh and tease people, but they are part of this traditional popular festivity which lasts 3 whole days.
If you have a spare time and happen to be in Brasilia, capital, don´t hesitate to rent a car and drive 140 kilometers to Pirenópolis, where besides watching this spectacular event, along with locals ( this is NOT Carnival and not the least a mass tourism attraction, as it´s not well known even among the Brazilians) and enjoy the atmosphere of this charming place. You´ll find very good pousadas as well as fantastic food, both regional as international. Also, the people of Goiás are (truly) reputed to be extremely hospitable- their doors are supposed to remain open all the time, to welcome visitors.