cattle is countable, yes, and the meaning is plural.
AND: we say "head of cattle" (also used with sheep) so that gives us this kind of sentence:
I have 20 head of cattle on my farm. [notice the singular]
I have many head of cattle on my farm. OR
I have a lot of cattle on my ranch.
I have three cattle on my farm. [not my personal preference]
Also from Wikipedia:
Cattle can only be used in the plural and not in the singular: it is a
plurale tantum.[31] Thus one may refer to "three cattle" or "some
cattle", but not "one cattle". "One head of cattle" is a valid though
periphrastic way to refer to one animal of indeterminate or unknown
age and sex; otherwise no universally used single-word singular form
of cattle exists in modern English, other than the sex- and
age-specific terms such as cow, bull, steer and heifer.
Please note: Personally, I would not use a number with cattle as explained above.
cattle
staff: We say: member of staff or staff members. How many staff members are there in your office? For a walking stick, the word is countable. The shepherds have staffs.
Jeans: He was wearing jeans. How many pairs [of jeans] does he own?
Jeans is plurale tantum:
A plurale tantum (Latin for 'plural only'; pl. pluralia tantum) is a
noun that appears only in the plural form and does not have a singular
variant for referring to a single object. In a less strict usage of
the term, it can also refer to nouns whose singular form is rarely
used.
'Putting on pants' is correct, 'putting on pant' sounds odd In
English, pluralia tantum are often words that denote objects that
occur or function as pairs or sets, such as spectacles, trousers,
pants, scissors, clothes, or genitals. Other examples are for
collections that, like alms and feces, cannot conceivably be singular.
Other examples include suds, jeans, outskirts, odds, riches,
surroundings, thanks, and heroics.
plurale tantum
https://en.wikipedia.org/wiki/Cattle#:~:text=%22One%20head%20of%20cattle%22%20is,%2C%20bull%2C%20steer%20and%20heifer.
Many is for countable nouns only. Much is for non-countable nouns. BUT beware of this: We don't say: I have much coffee (usually). We use: I have a lot of coffee [in the cupboard]. a lot of is preferred to much in many declarative situations.