so with females having double uterus i have an idea for the male version
high fertility / high potency (whatever the admins what to name it)

basically the sperm count of the males would be exceedingly high
it would make it easier to breed females with vary low fertility
and can but NOT always produce more cubs that still depends on females egg count

the mutation would be just as rare as double uterus and only available for males

in the wild male lions have really crappy fertility thats why it takes 100+ mateing sessions to produce just one cub and this mutation can actually happen out in the wild also