I always figured at around 4-5 sweeps the lusii are less focused on providing for them and more on defending the homestead, keeping dangerous shit off their territory. Possibly dragging hive dead things but they wouldn't be pleasant to eat or smell
I don’t think there’s really that much of a distinction between the two phases; the lusus is a “”domesticated”” animal whose job is to raise the troll as its own child, and that involves both defending their mutual hive and feeding them (even beyond the point at which the troll can feed themselves, which is where we get the lusus dragging ‘useless’ dead things hive from - they are very much valid food, just not as good as pizza you can order from a store).
I think 4-5 is a pretty unlikely cutoff point too since that seems like the age whereafter trolls would start to venture outside their hives a lot more, and we can see pretty plainly that trolls bring their lusii places.