## The 21-Day Protocol

Introducing two cats **too quickly** is the best way to ensure months of tension, hissing, ambushes, litter boxes soiled due to stress, and sometimes even real fights. It’s a mistake that can cause difficulties in cohabitation for **years**.

The "21-Day" protocol, developed by feline ethologists, ensures:
- **85-90%** success in introductions.
- Peaceful cohabitation in **3-4 weeks**.
- Drastic reduction of stress for both cats.

Here’s how it works, step by step.

## Why 21 Days

Three weeks is the average time needed for a cat's nervous system to:
- **Get used to the smell** of a new cat.
- **Process the novelty** without acute stress.
- **Establish peaceful social dynamics**.

Shorter times = acute stress. Longer times = habituation completed, but sometimes additional details to be defined.

## Phase 1 (Days 1-7): Total Separation + Scent Exchange

**Initial Setup**:

The new cat stays in a **separate safe room** from the resident cat. The door is closed, but the two cats can "sniff" each other through the crack.

**What to do each day**:

**Step A: Scent Exchange.**
Take a **cloth** or small **towel**, rub it on the face and body of one cat. Place it in the other cat's room. Reward if the cat sniffs it calmly.

**Step B: Room Exchange.**
Once a day, **swap** the cats’ rooms. The new cat goes to the living room (where you’ve placed the resident cat in a different room). The resident cat enters the safe room. They start to familiarize themselves with each other’s scents.

**Step C: Meals Near the Door.**
Place bowls of **tasty food** (pâté, chicken) **near the closed door**. Both eat simultaneously, with the door between them. They associate "presence of the other" + "good food".

**Step D: Play Near the Door.**
Play with a feather wand from both sides of the door. Both cats play, associating the presence of the other with positive experiences.

**What NOT to do**:
- Open the door to "let them see each other".
- Force interaction.
- Show one cat to the other.

**Signs of Progress**:
- Decrease in hissing/growling (even through the door).
- Eating without signs of stress near the door.
- Curiosity towards the other’s scent.

**Signs of Problems**:
- Intense hissing/growling.
- Refusal to eat.
- Litter box soiled due to stress.

If problems arise: extend Phase 1 (even up to 14 days).

## Phase 2 (Days 8-14): Limited Eye Contact

After the first week, if things are going well, begin **limited eye contact**.

**Setup**:

Replace the closed door with a **pet gate** (a high gate) or **netting**. The cats can see each other but cannot touch.

**What to do each day**:

**Step A: Short Viewing Sessions.**
Open the gate for **5-10 minutes**, 2-3 times a day. The cats see each other. You observe.

**Step B: Distract with Food or Play.**
During the sessions, distract both with treats or toys. They associate seeing each other with good things.

**Step C: Gradually Increase.**
If they remain calm: 10 minutes → 15 minutes → 20 minutes → 30 minutes.

**What NOT to do**:
- Let them see each other for hours (overload).
- Force proximity.
- Scold defensive reactions (hissing, moves).

**Signs of Progress**:
- They look at each other without visible tension.
- They eat together calmly.
- Spontaneous approach to the gate.
- Regular bathroom habits for both.

**Signs of Problems**:
- Persistent hissing/growling.
- Defensive posture (arched back, raised fur).
- Visible stress.

If problems arise: return to Phase 1 for another 2-3 days, then try again.

## Phase 3 (Days 15-21): First Direct Contacts

Final week: **face-to-face meetings**.

**Setup**:

Remove the gate. The cats can interact directly, under **constant supervision**.

**What to do each day**:

**Step A: First Short Sessions (Days 15-17).**
- **5-10 minutes** of direct interaction.
- **You are present, attentive, calm**.
- If either shows stress, separate them.

**Step B: Gradually Increase (Days 18-21).**
- 15 minutes → 30 minutes → 1 hour.
- Let them interact without intervening (unless there’s aggression).
- Distract with food or play if there’s tension.

**Step C: Pair in Common Space.**
- Common spaces for most of the day.
- Safe room open as a "refuge" for the newcomer.

**What NOT to do**:
- Leave them completely alone for hours.
- Expect immediate happy play.
- Stress if there are normal hisses (social calibration).

**Signs of Success**:
- Peaceful coexistence.
- Eventually playing together.
- Mutual grooming (top sign of success).
- Sleeping in the same room.

## Signs of Success

After 21 days, you can expect:

**"Good" Success**:
- The cats coexist peacefully.
- They never fight.
- They eat in the same rooms.
- They ignore each other cordially.

**"Excellent" Success**:
- Shared play.
- Mutual grooming.
- They sleep together or in the same room.
- They actively seek each other.

**"Perfect" Success (rare)**:
- Deep friendship.
- Inseparable.
- Constant communication.

Don’t expect "perfect" success after 21 days: it’s the result of months/years of cohabitation that may evolve.

## What to Do If the Introduction Fails

**Signs of Failure**:
- Real fights with injuries.
- One of the cats shows symptoms of chronic stress (stops eating, soils due to stress, hides constantly).
- Constant tension that does not reduce.

**What to Do**:

**1. Go back** to the previous phase (e.g., from phase 3 to phase 2).

**2. Extend the timing**: in some cases, it takes 6-8 weeks instead of 3.

**3. Consult a veterinary behaviorist**: they may prescribe temporary anxiolytics.

**4. Reconsider compatibility**:
- Are they both too dominant?
- Are the ages very different (e.g., senior + hyperactive kitten)?
- Is there a character incompatibility (shy + outgoing)?

**5. Any territorial solutions**:
- Permanent separate rooms.
- Cohabitation in "turns".
- Surrender: in some cases, incompatibilities cannot be overcome. Finding a new family for one may be the best option.

## Essential Resources at Home

To reduce competition and conflicts:

**Litter Boxes**: follow the "N+1" rule (one more litter box than the number of cats you have). Two cats = 3 litter boxes.
**Water Bowls**: minimum of 2-3 in different locations.
**Food Bowls**: at least 2, even if they eat the same thing.
**Scratching Posts**: at least 2, in different areas.
**Resting Spots**: many, at different heights.
**Hiding Places**: 4-5 around the house (boxes, shelves, under furniture).

In a "resource-rich" environment, competition dramatically decreases.

## Long-Term Management

Even after a successful introduction, maintain:

**1. Separate spaces/resources**: each has their preferred "things".

**2. Separate time with the two cats**: play, cuddle each individually.

**3. Constant observation**: small conflicts that escalate should be managed immediately.

**4. Environmental adjustments**: as one grows, the other ages, life events - cats change over time.

## Timing Makes a Difference

Pairs of cats adopted together as siblings: cohabitation is often excellent for life.

Adults introduced together well: generally peaceful cohabitation.

Adults introduced poorly: years of tension, sometimes irrecoverable.

Investing **3 weeks** of patience at the beginning grants you **15+ years** of peaceful cohabitation. It is the best time you can invest in a multi-species relationship.