Dogs are disliked in Islam because they are filthy and impure. However, guide dogs or dogs for farming and hunting are permissible, because there is a need to have them.
The Prophet, peace and blessings be upon him, said: Whoever keeps a dog, one Qirat of the reward of his good deeds is deducted daily, unless the dog is used for guarding a farm or cattle. 
He also said: If a dog licks a vessel, wash it seven times and rub it with dust the eight times. 
However, Muslims must still look after animals if they are in a bad state, for example if they are hungry or thirsty.
The Prophet said: A man saw a dog eating mud from (the severity of) thirst. So, that man took a shoe (and filled it) with water and kept on pouring the water for the dog till it quenched its thirst. So Allah approved of his deed and made him to enter Paradise.