I'm sorry, I'm not 100% sure what you are trying to do (
You've obviously got a database related to horses (breeding?). Am I correct
in thinking what you want is for each stallion to be linked to a number of
different mare records?
If this is the case, then you have what is called a one-to-many relationship
(each stallion can be associated with many mares).
You should probably have three database tables here:
table of stallions
table of mares
table of links
(you could just have a links table and a table of horses, but I'm using
mares & stallions separately as it makes explanation easier!)
the table of links basically will hold the stallion id and the mare id, plus
an (autonumber?) link id.
On the stallion form, you want to create a subform based on the links table.
The child/parent properties should be based on stallion ID. On this form, add
a combo box (aka drop box/ aka dropdown box/ aka lots of other things), with
an datasource of the table of mares. The fields in the combo box will
probably be mare_id (this should be the source) and mare name. You probably
want the combo to not show the mare id but just show the mare name.
Each of these steps could be broken down a lot further but this should
hopefully point you in the right direction!