Veterinarski pregled je prije cjepiva i kastracije.

Because veterinarski is an adjective modifying pregled.

In Croatian, adjectives agree with the noun they describe in:

• gender
• number
• case

Here, pregled is:

• masculine
• singular
• nominative (the subject of the sentence)

So the adjective also appears in the masculine singular nominative form:

• veterinarski pregled = veterinary examination / vet check-up

If the noun changed, the adjective would change too.

Because they come after prije, and prije normally requires the genitive case.

So:

• cjepivo → cjepiva
• kastracija → kastracije

This is very common in Croatian: a preposition often determines the case of the noun that follows it.

So the structure is:

• prije + genitive

That is why you do not say prije cjepivo i kastracija here.

Here is the case breakdown:

• veterinarski pregled — nominative singular
  This is the subject: the vet examination/check-up

• cjepiva — genitive singular
  Used because it follows prije

• kastracije — genitive singular
  Also used because it follows prije

So the sentence is built around:

• [subject in nominative] + je + [prije + genitive]

Je is the 3rd person singular present form of biti = to be.

So here it simply means is:

• Veterinarski pregled je prije...
• The veterinary examination is before...

Croatian often uses forms of biti the same way English uses to be.

You generally need je here, because the sentence is making a statement of the type X is before Y.

Standard Croatian does not use articles like English a/an and the.

So:

• pregled can mean an examination, the examination, or just examination
• the exact meaning depends on context

That is completely normal in Croatian. Learners often expect a separate word for the, but there usually is none.

In this sentence, prije means before in the time/order sense.

So it means something like:

• the vet check happens earlier than the vaccine and the castration

For physical position, Croatian usually uses something else, such as ispred = in front of.

So:

• prije cjepiva i kastracije = before the vaccine and castration
• not in front of the vaccine and castration

Not exactly.

• cjepivo usually means vaccine
• cijepljenje usually means vaccination

So, very literally, prije cjepiva is before the vaccine.

Depending on context, English may translate it more naturally as before vaccination, but the Croatian word here is still cjepivo.

A learner may sometimes hear both:

• prije cjepiva = before the vaccine
• prije cijepljenja = before vaccination

Yes, Croatian word order is more flexible than English word order.

The neutral order here is:

• Veterinarski pregled je prije cjepiva i kastracije.

But Croatian can move elements around for emphasis, for example:

• Prije cjepiva i kastracije je veterinarski pregled.

That still makes sense, but it sounds more marked or focused. For learners, the original version is the safest and most neutral one to use.

A rough pronunciation guide:

• Veterinarski ≈ veh-teh-ree-NAR-skee
• pregled ≈ PREH-gled
• je ≈ yeh
• prije ≈ PREE-yeh
• cjepiva ≈ TSYEH-pee-va or CYEH-pee-va
• i = ee
• kastracije ≈ kah-strah-TSEE-yeh

A rough full reading:

• veh-teh-ree-NAR-skee PREH-gled yeh PREE-yeh TSYEH-pee-va ee kah-strah-TSEE-yeh

The cluster cj in cjepiva can feel difficult for English speakers. It is not pronounced like English j in jam.

Yes, it is understandable and natural.

• veterinarski = veterinary / vet-related
• pregled = examination / check-up

So veterinarski pregled is a normal phrase for a veterinary examination.

You might also hear other natural expressions depending on context, such as:

• pregled kod veterinara = an examination at the vet's
• veterinarski pregled životinje = veterinary examination of the animal

But the phrase in your sentence is perfectly fine.