Vacca, cuius vitulus prope stat, iterum mugit.

Vacca is nominative singular. It is the subject of the main verb mugit (moos), so it has to be in the nominative.

So the basic main clause is:

• Vacca ... mugit = The cow ... moos

Everything in between is extra information about that cow.

Cuius means whose.

It is the genitive singular form of the relative pronoun qui, quae, quod. In this sentence, it introduces a relative clause:

• cuius vitulus prope stat = whose calf stands nearby

Literally, cuius can mean of whom, of which, or whose, depending on context. Here whose is the most natural English translation.

Because the pronoun’s case is determined by its job inside its own clause, not just by the noun it refers to.

Here, cuius refers back to vacca (cow), but inside the relative clause it shows possession:

• the calf of the cow
• therefore Latin uses the genitive: cuius

If the pronoun were the subject of the relative clause, then you might get quae instead. But here the subject of the relative clause is vitulus, not the pronoun.

Yes, but only in the way relative pronouns normally agree.

A relative pronoun agrees with its antecedent in:

• gender
• number

but its case depends on its role in the relative clause.

So here:

• antecedent: vacca = feminine singular
• pronoun: refers to that same noun
• but its role is possessive, so it appears in the genitive singular: cuius

One thing that can confuse learners is that cuius has the same form for masculine, feminine, and neuter singular. So even though it refers to a feminine noun here, the form is still cuius.

Because vitulus is the subject of stat in the relative clause.

The relative clause is:

• cuius vitulus prope stat

and the structure is:

• vitulus = subject
• stat = stands
• prope = nearby

So vitulus is nominative singular: the calf stands nearby.

Here prope means nearby or close by.

In this sentence it is being used as an adverb, not as a preposition.

So:

• prope stat = stands nearby

This is important because prope can also be a preposition meaning near, in which case it takes an accusative object:

• prope villam = near the farmhouse

But in your sentence there is no object after prope, so it is best understood as an adverb.

Stat means stands or is standing, from stare.

Latin often prefers a more vivid, specific verb where English might sometimes use is. So:

• vitulus prope stat = the calf stands nearby

This suggests the calf is physically standing close to the cow, not just existing there.

If Latin had used est, the meaning would be more like is nearby, which is possible in some contexts, but less concrete.

Mugit is:

• 3rd person singular
• present tense
• indicative
• active
• from mugire = to moo, to low

It agrees with vacca, which is a singular subject.

So:

• vacca mugit = the cow moos

Iterum means again.

It is an adverb, modifying mugit:

• iterum mugit = moos again

It tells you that the action is repeated.

Latin word order is much more flexible than English word order.

Placing iterum before mugit is perfectly natural and keeps the adverb close to the verb it modifies:

• iterum mugit = moos again

Latin often puts adverbs before verbs, but other placements are also possible depending on emphasis.

Because it describes vacca.

The main idea is:

• Vacca iterum mugit = The cow moos again

The relative clause:

• cuius vitulus prope stat = whose calf stands nearby

is inserted right after vacca to identify or describe the cow more fully.

So the sentence is structured like this:

• Vacca — the main subject
• cuius vitulus prope stat — extra information about that subject
• iterum mugit — the main action

Grammatically, cuius does literally mean something like of whom or of which, but English normally translates it as whose when it shows possession.

So although a very literal breakdown can help with grammar:

• cuius vitulus = the calf of whom/of which

the natural English is:

• whose calf

That is why The cow, whose calf stands nearby, moos again is the best translation.

The commas show that cuius vitulus prope stat is extra descriptive information.

In modern printed Latin, punctuation is used to help the reader, much as it is in English. The commas mark off the relative clause:

• Vacca, cuius vitulus prope stat, iterum mugit.

This helps you see the main clause more easily:

• Vacca ... iterum mugit

Without the punctuation, the grammar would still work, but it would be slightly harder for a beginner to parse.