In order to register a reproductive loss first of all you must access
Breeding > Data Entry > Reproductove Losses
1 - Add the kind of reproductove loss ( Abortion, Return to estrus or not pig in sow)
2 - Fill with the sow's Id
3- Date the loss ocurred.
After filling all the data just click on the "save and close (if there is no other entry to add) or Save and continue (to add another loss).