Incorrect amount of damage heart particles shown when hitting some entities for the first time

When you hit a horse, donkey, llama or mule spawned from /summon or a spawn egg for the first time, numerous damage heart particles will appear that do properly represent the damage the entity took.

Steps to Reproduce:

1. Summon a horse, donkey, llama or mule
2. Hit the entity
   → Multiple damage hearts appear
3. Hit the entity again
   → No damage heart appears

Expected Result:

The damage hearts would properly reflect how much damage the entity took.

Screenshots: