"Her clothes are beautiful." Uncountable.
"Cattle" is always uncountable. "Poultry", on the other hand, is a category like "meat". For example "Poultry is something that a chef should ...". Poultry exists only in the singular, never in the plural.
"And one more question: is noun always classified either as countable or uncountable?"
Nouns are almost always either countable or not. There are a very few exceptions. For example one can say "Oats are a nutritious food", and "Oats is the only cereal crop that can be grown north of 56 degrees north latitude."
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