Nel pascolo il cavallo corre, mentre il vitello cammina lentamente accanto alla mucca.

Nel is a contraction of in + il.

Italian very often combines a preposition with the definite article:

• in + il = nel
• a + la = alla
• di + il = del

So nel pascolo means in the pasture. Using in il would sound incorrect in standard Italian.

Italian uses definite articles much more often than English. With nouns in general, and very often with animals, Italian normally includes the article where English might not.

So:

• il cavallo
• il vitello
• la mucca

This is completely natural in Italian. Leaving out the article here would usually sound incomplete or unnatural.

Italian word order is more flexible than English word order. Starting with Nel pascolo puts the setting first: In the pasture...

The sentence could also be rearranged, for example:

• Il cavallo corre nel pascolo, mentre il vitello...

But the original version sounds natural and helps establish the scene before introducing what the animals are doing.

Mentre links the two parts of the sentence and means while or sometimes whereas, depending on context.

Here it connects two actions happening in the same scene:

• il cavallo corre
• il vitello cammina lentamente accanto alla mucca

So mentre shows that one action is happening while the other is also taking place.

They are both third-person singular present tense forms:

• correre → corre = he/she/it runs
• camminare → cammina = he/she/it walks

They match the subjects:

• il cavallo corre
• il vitello cammina

In Italian, the verb ending already shows the person and number, so you do not need a separate subject pronoun like it.

In Italian, adverbs often come after the verb, especially in simple sentences.

So:

• cammina lentamente = walks slowly

That placement is very common and natural. Italian can sometimes move adverbs for emphasis, but here cammina lentamente is the most straightforward choice.

Accanto a is a fixed expression meaning next to or beside.

Because mucca is feminine singular and uses the article la, the preposition a combines with la:

• a + la = alla

So:

• accanto alla mucca = next to the cow

This is the same kind of contraction as nel.

Yes. Italian allows some flexibility.

For example, you could say:

• Il vitello cammina accanto alla mucca lentamente
• Accanto alla mucca, il vitello cammina lentamente

But the original order, cammina lentamente accanto alla mucca, is very natural because it moves from the action to the manner to the location.

Italian often uses the simple present to describe actions happening now, general scenes, or narrative description.

So:

• corre
• cammina

can describe what is happening in the scene right now. English sometimes prefers is running or is walking, but Italian often uses the simple present in this kind of sentence.

The comma separates the two clauses and makes the sentence easier to read:

• Nel pascolo il cavallo corre
• mentre il vitello cammina lentamente accanto alla mucca

With mentre, a comma is often used when the sentence has two clearly distinct parts, especially in descriptive writing. It helps mark the pause, although punctuation can vary depending on style.