kanzensitunaigai to dassoubousi ga hituyou desu.

It is read:

完全室内飼い（かんぜんしつないがい）と脱走防止（だっそうぼうし）が必要です（ひつようです）。

A few reading notes:

• 室内飼い is read しつないがい
• 飼い becomes がい here because of voicing in the compound
• 必要です is the polite ending

完全室内飼い is a noun phrase.

• 完全 = complete / full / strict
• 室内 = indoors
• 飼い = keeping/raising an animal

So the phrase means something like strictly keeping the animal indoors or full indoor-only keeping.

In natural English, you would usually translate it with a verb, but in Japanese it is packaged as a noun-like expression.

Because this is not being used as a full verb here. It is part of a compound noun.

• 飼う = to keep / to raise an animal
• 飼い = the verb stem, which can appear in compound nouns

So 室内飼い is a set noun meaning indoor keeping.

This is common in Japanese. Compare similar patterns like:

• 持ち帰り = takeout
• 立ち入り禁止 = no entry

So 飼い here is not a conjugated sentence-ending verb. It is part of a noun expression.

It is a compound noun made from two Sino-Japanese words:

• 脱走 = escape / breaking out / running away
• 防止 = prevention

Together, 脱走防止 means escape prevention or preventing escape.

In context, it usually means taking steps so the animal cannot get out, such as secure doors, windows, screens, carriers, and so on.

Here と works like and.

It connects two nouns:

• 完全室内飼い
• 脱走防止

So:

A と B が必要です
= A and B are necessary

This is a very standard way to list nouns in Japanese.

Because the whole phrase 完全室内飼い と 脱走防止 acts as one combined subject of 必要です.

So the structure is:

• [A と B] が 必要です
• [A and B] are necessary

Japanese does not need to mark each item separately. The entire A and B phrase gets one が.

が marks the thing that is necessary.

So:

• 完全室内飼いと脱走防止が必要です
  = Complete indoor keeping and escape prevention are necessary

If you used は, it would sound more like setting those items up as a topic, often with some contrast or emphasis:

• 完全室内飼いと脱走防止は必要です

That could sound like As for complete indoor keeping and escape prevention, those are necessary.

So が is the more neutral and straightforward choice here.

必要 is a na-adjective (also called an adjectival noun).

That means it can work like this:

• 必要です = is necessary
• 必要な条件 = a necessary condition
• 必要があります = there is a need

In this sentence, 必要です is the predicate, so the whole sentence means that those things are necessary.

That is normal in Japanese. The sentence depends on context.

Japanese often leaves out things that are obvious from the situation. In a pet adoption notice or care instructions, the understood meaning would be something like:

• The adopter must keep the animal strictly indoors and prevent escape
• For this animal, indoor-only keeping and escape prevention are required

So the responsible person is not named in the sentence because the surrounding context usually makes it clear.

Yes, and that is often the most natural English.

Japanese often uses noun phrases plus 必要です, while English often prefers verbs. So a natural English rendering might be:

• You must keep the animal strictly indoors and prevent it from escaping.

That sounds more natural in English, even though the Japanese literally uses noun-style expressions:

• complete indoor keeping
• escape prevention

So this is a good example of Japanese and English preferring different sentence shapes.

It is polite and fairly formal because it ends with です.

It sounds very natural in places like:

• adoption requirements
• rules for pet ownership
• notices from shelters or rescue groups
• written instructions

It is concise and matter-of-fact, which is common in Japanese notices and guidelines.