The maxcount didn't change as far as I can tell. I gave you the full change of the lines.
Here's what a full block looks like in the current A19 b163
<biome name="pine_forest">
<spawn maxcount="1" respawndelay="3" time="Day" entitygroup="ZombiesAll" />
<spawn maxcount="1" respawndelay="4" time="Night" entitygroup="ZombiesNight" />
<spawn maxcount="1" respawndelay="7" time="Any" entitygroup="EnemyAnimalsForest" spawnDeadChance="0" />
<spawn maxcount="1" respawndelay="10" time="Any" entitygroup="FriendlyAnimalsForest" spawnDeadChance="0" />
</biome>
And here's the same block in A18.4
<biome name="pine_forest">
<spawn maxcount="1" respawndelay="3" time="Day" entitygroup="ZombiesAll" />
<spawn maxcount="1" respawndelay="4" time="Night" entitygroup="ZombiesNight" />
<spawn maxcount="1" respawndelay="14" time="Any" entitygroup="EnemyAnimalsForest" spawnDeadChance="0" />
<spawn maxcount="1" respawndelay="21" time="Any" entitygroup="FriendlyAnimalsForest" spawnDeadChance="0" />
</biome>
The important changes are in entitygroups.xml
For example this:
A19 B157:
<entitygroup name="EnemyAnimalsForest">
! <entity name="invisibleAnimalEnemy" prob="6"/>
! <entity name="animalWolf" prob="0.4"/>
! <entity name="animalBear" prob="0.05"/>
! <entity name="animalDireWolf" prob="0.05"/>
! </entitygroup>
A19 B163:
<entitygroup name="EnemyAnimalsForest">
! <entity name="invisibleAnimalEnemy" prob="80"/>
! <entity name="animalWolf" prob="10"/>
! <entity name="animalBear" prob="5"/>
! <entity name="animalDireWolf" prob="5"/>
! </entitygroup>
If I read this correctly, previously an unfriendly animal would spawn in 1 of 12 spawn events only, in the forest. Now it is 1 in 5, that is more than doubled.
Friendly animals in forest jumped from 2 in 3 to always.
PS: It is entirely possible that I don't interpret the numbers correctly. Especially the friendly animals increase of only 30% does not seem enough to explain the observations of players at the moment.