Praise be to Allah.
This question is in two parts:
1 – what is the fate of animals in the Hereafter? Allaah says (interpretation of the meaning):
“And when the wild beasts shall be gathered together”
“There is not a moving (living) creature on earth, nor a bird that flies with its two wings, but are communities like you. We have neglected nothing in the Book, then unto their Lord they (all) shall be gathered”
Ibn ‘Abbaas said: “Everything will be gathered, even the flies.”
On the Day of Resurrection, the animals will settle scores between one another. It says in a hadeeth of Abu Hurayrah that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “All scores will be settled on the Day of Resurrection; even the hornless sheep will settle its scores with the horned sheep.” (Narrated by Muslim, al-Birr wa’l-Silah wa’l-Adaab, 4679).
It says in another hadeeth: “Allaah will judge between His creation, jinn, humans and animals. On that Day the score will be settled between the hornless and the horned, until there are no outstanding issues left, then Allaah will say, ‘Be dust!’ At the point the kaafir will say, ‘Would that I were dust!’” Shaykh al-Albaani said: This is saheeh. No. 1966; see al-Silsilah al-Saheehah, part 4, p. 966
What is obligatory for the Muslim is to be kind to animals and not harm or annoy them. It was reported that a woman was punished because of a cat. Al-Bukhaari narrated from Ibn ‘Umar (may Allaah be pleased with them both) that the Prophet (peace and blessings of Allaah be upon him) said: “A woman went to Hell because of a cat which she tied up, and did not feed it or let it eat of the vermin of the earth.” (Bad’ al-Khalq, 3071)
And Allaah forgave a prostitute because she was kind to a dog. Al-Bukhaari also narrated that Abu Hurayrah (may Allaah be pleased with him) said: “The Messenger of Allaah (peace and blessings of Allaah be upon him) said: ‘Whilst a dog was walking around a well, almost dying of thirst, one of the prostitutes of Bani Israa’eel saw him, took off her shoe and gave him water. She was forgiven because of that.” (Ahaadeeth al-Anbiyaa’, 3208)
Whoever harms an animal has to repent to Allaah for that, because the Lord of the animals is the One Who has commanded us to be kind towards them (unless they are harmful).