El conejo come pienso especial, y la veterinaria dice que es mejor no darle pan.

Because pienso can be either:

• the 1st person singular of pensar: I think
• a noun meaning animal feed, especially dry feed

Here it follows come, so the context makes it clear that pienso is the noun. In Spain, pienso is a very common word for food made for animals.

In Spanish, adjectives usually come after the noun, especially when they are simply describing it.

So:

• pienso especial = special feed

Putting especial before the noun would sound unusual here. In general, post-noun adjective order is the normal pattern in Spanish.

Because both are being used in a general, non-specific way.

• come pienso especial = it eats special feed
• no darle pan = not give it bread

Spanish often leaves out the article with food or materials when speaking generally, especially after verbs like comer, beber, or dar.

Compare:

• Come pienso especial = It eats special feed in general.
• Come el pienso especial = It eats the specific special feed we already know about.

And:

• No darle pan = not give it bread in general
• No darle el pan = not give it the bread, a specific bread already mentioned

Yes, most naturally la veterinaria here means the female veterinarian.

Spanish often marks profession words for gender:

• el veterinario = male vet
• la veterinaria = female vet

In some contexts, la veterinaria can also mean the veterinary clinic, but in this sentence, because it says dice, the most natural reading is the female vet says.

Because Spanish normally uses que to introduce a reported statement after verbs like decir, pensar, creer, and saber.

So:

• dice que es mejor... = she says that it is better...

In English, that is often optional, but in Spanish que is usually required here. You cannot normally say dice es mejor.

Because decir que is introducing a statement presented as information or opinion, so Spanish uses the indicative:

• dice que es mejor...

The subjunctive is not triggered just by decir itself. You usually get the subjunctive after expressions of doubt, emotion, influence, or unreality, not in a straightforward reported statement like this one.

This is a very common structure:

• es mejor + infinitive = it is better to...
• no + infinitive = not to...

So:

• es mejor no darle pan = it is better not to give it bread

The negative no goes before the infinitive darle.

You could think of it as:

• es mejor = it is better
• no darle pan = not to give it bread

Le refers to the rabbit.

The verb dar works like to give something to someone:

• dar pan al conejo = to give bread to the rabbit

That to the rabbit part is an indirect object, and Spanish commonly replaces it with le:

• darle pan = to give it/him bread

So in this sentence, le means to the rabbit.

Because with an infinitive, object pronouns can be attached to the end.

So:

• darle = to give it / to give him / to give her

This is normal after infinitives. Spanish also allows the pronoun before a conjugated verb in other structures, but here the infinitive form makes attachment natural.

For example:

• Quiero darle pan = I want to give it bread
• No es bueno darle pan = It is not good to give it bread

Yes. That would also be correct.

You have a few possible versions:

• no darle pan
• no darle pan al conejo
• no dar pan al conejo

Adding al conejo makes the recipient explicit. Without it, le already tells us who receives the bread, and the context makes it clear that it is the rabbit.

Spanish often uses both the pronoun and the noun together:

• darle pan al conejo

That is very common and natural.

Because the sentence is describing a habit or a general fact, not something happening right now at this exact moment.

• come = eats / does eat
• está comiendo = is eating right now

So:

• El conejo come pienso especial = The rabbit eats special feed.
• El conejo está comiendo pienso especial = The rabbit is eating special feed right now.

The simple present is the normal choice for routines, habits, and general truths.

Because singular count nouns in Spanish usually need a determiner such as an article.

So Spanish normally says:

• el conejo
• un conejo

Just conejo by itself would usually sound incomplete in a sentence like this.

Also, Spanish uses the definite article more often than English does. Here el conejo most likely refers to a specific rabbit already known in the conversation.

Because the sentence joins two full clauses with different subjects:

• El conejo come pienso especial
• la veterinaria dice que es mejor no darle pan

In Spanish, a comma before y is often omitted in simple combinations, but it can appear when:

• the clauses are longer
• there is a change of subject
• the writer wants clearer separation

So this comma is natural and acceptable, though in shorter or simpler sentences you often would not see one before y.