Hello Anke and welcome to Writefix!
Thanks for your excellent 336-word essay on this emotive topic.
Your introduction is short but very strong - almost unassailable, in fact! In three short and simple sentences, you cover both sides of the issue, state the situation, give your opinion, and follow the instruction (in IELTS) to 'use details from your own experience.'
In Paragraph 2 you discuss the continuing search for new remedies and the development of new procedures. You state that both of these result in a need for testing, and that testing results in many dangerous drugs and procedures being withdrawn that would otherwise cause problems.
In Paragraph 3 you give some more details of your experience, and explain why animals are used and under what circumstances or controls.
In Paragraph 4 you suggest that many people are against animal testing because they don't have enough information about it. You also explain why computer simulations are not enough. (This sentence about simulations might have been better placed in Paragraph 2 - what do you think?)
Finally, in your conclusion you give your opinion, state what is necessary to ensure that animals do not suffer too much, and suggest a course of action ('Researchers should provide the public with information...')
One small point:
Don't join sentences with 'nevertheless' or 'however' - the result is a comma splice or a run-on sentence.
Medical knowledge is improving at a fast rate, nevertheless there are still many diseases that cannot be cured...
Just use a full stop, or a semicolon:
- Medical knowledge is improving at a fast rate. Nevertheless, there are still many diseases that cannot be cured...
- Medical knowledge is improving at a fast rate; nevertheless, there are still many diseases that cannot be cured....
I hope we can see some more essays from you!