When (if?) do you lose the “u”

Quick question but I’m unaware if this is intentional or just the speaker (but I’ve noticed it on many apps) but as title, when do you lose the U sound, if at all?

Example

Meat = “nik**u**”

Speakers always clearly pronounce the U, except for desu (at least, I never hear it) but meat and rice = “nik to gohan”

It sounds simple enough but I’ve noticed it with most stuff when adding continuation. Is this correct? Sorry for the basic question.