"I like pigs a lot."

Translation: Is toil leam mucan gu mòr.

[Katiepeheakoe]

So when it's not a number, i use mucan instead of mhucan?

[silmeth]

You might want to read the tips and notes to the lessons, they explain those things.

mucan is the default plural form meaning pigs, it may get lenited in some contexts (like after some, but not all, numerals) to mhucan – but lenition might be caused by other things too, not just the numbers (and some numbers take singular form rather than plural too).

You can find the tips and notes in the web browser version of Duolingo at https://duolingo.com (unfortunately not in the mobile app), or also on: https://duome.eu/tips/en/gd