Vacunar protege la salud del cachorro.

Because here vacunar is being used as a general action, not as someone vaccinates.

In Spanish, an infinitive can act like a noun-like subject:

• Fumar es malo. = Smoking is bad.
• Leer ayuda mucho. = Reading helps a lot.
• Vacunar protege... = Vaccinating protects...

So vacunar is the subject of protege.

The main conjugated verb is protege.

• vacunar = infinitive, functioning as the subject
• protege = present tense, he/she/it protects
• la salud del cachorro = the object of protege

So the structure is basically:

[Vacunar] [protege] [la salud del cachorro].

Because the subject is treated as a single action: vacunar.

Even though English might feel like it refers to many situations in general, Spanish sees vacunar as one idea, so the verb is singular:

• Vacunar protege...
• Comer bien ayuda.
• Dormir suficiente mejora la salud.

If the subject were plural, then you would use protegen:

• Las vacunas protegen la salud del cachorro.

Del is the contraction of de + el.

• de = of
• el = the
• de + el = del

So:

• la salud del cachorro = the health of the puppy

This contraction is mandatory in Spanish whenever de is followed by el (except with proper names like de El Salvador).

Spanish often prefers a more explicit phrase like la salud del cachorro when it wants to avoid ambiguity.

Su salud could mean:

• his health
• her health
• its health
• their health
• your health (formal)

So la salud del cachorro is clearer and more specific.

Both are possible in the right context, but la salud del cachorro is very clear and natural.

Because del cachorro is not the direct object of vacunar here.

In this sentence:

• vacunar is being used in a general sense: vaccinating
• la salud is what gets protected
• del cachorro tells you whose health

So del cachorro belongs with la salud, not with vacunar.

If you wanted to say Vaccinating the puppy protects its health, then you would usually include the personal a:

• Vacunar al cachorro protege su salud.

There, al cachorro is the direct object of vacunar.

Yes. That is also correct and very natural.

The difference is mostly in style:

• Vacunar protege... = Vaccinating protects...
  Focuses on the action itself.
• La vacunación protege... = Vaccination protects...
  Sounds a bit more formal or technical.

Both are good Spanish.

Cachorro usually means puppy, especially in everyday use.

More broadly, it can also mean the young of an animal, depending on context. In some contexts it can refer to a cub or young animal in general.

In a sentence about vaccines and health, learners will usually understand cachorro as puppy.

It can depend on context.

Del cachorro literally looks like of the puppy, which can suggest a specific puppy. But Spanish sometimes uses the singular definite article in general statements too, especially when talking about a type or category.

So depending on context, it may feel like:

• a specific puppy, or
• the puppy as a representative case

If the speaker wanted to sound more obviously general, they might say something like:

• Vacunar protege la salud de los cachorros.
• La vacunación protege la salud de los cachorros.

It is pronounced roughly pro-TE-he in much of Latin America, with the stress on the te syllable.

There is no written accent because, by standard Spanish stress rules, a word ending in a vowel is normally stressed on the second-to-last syllable. Protege already follows that rule, so no accent mark is needed.

Also, in most of Latin America, the g before e sounds like a strong h sound in English:

• protege ≈ pro-TE-he

Yes. Spanish often allows a short, general statement like this, but you can make it more explicit:

• Vacunar al cachorro protege su salud.
• La vacunación del cachorro protege su salud.
• Vacunar a los cachorros protege su salud.

These versions make the relationship clearer for learners because they directly mention who is being vaccinated. The original sentence is still grammatical and natural, especially in educational or informational language.