A single boar may be set up in a harem
with from four to 20 sows, although 10 females is generally considered to
be optimal. This system probably provides maximum production per unit
of space and expense, and is generally used for out-cross, conventional
breeding. A thriving, polygamous group will contain young in all stages
from birth to weaning, at any given time. As a consequence, it is
important to remove weanlings at 21 days to ensure that they do not get
bred by their sires. A further problem encountered is one where older
offspring in the group nurse the recently freshened sows (sows will usually
permit this) and consequently deprive the neonates of adequate milk. This
may be partially prevented by prompt removal of all juveniles;
alternatively, the sow and her litter may be removed to a separate cage a
few hours after birth (subsequent to post partum breeding). Yet another
problem may be stampeding, with trampling of the young, amongst
guinea pigs in a heavily populated floor pen harem.