Mares that are older than 18, or have a history of failing to go in foal or losing pregnancies, are often considered to be difficult breeders and may need special attention.
Problems that mares may have are usually either going in foal, or holding a pregnancy to term and a successful outcome.
Some mares that have failed to go in foal in the past may have poor perineal or uterine conformation, or a damaged endometrium, which lead them to retain fluid and become infected. These mares should be assessed, diagnosed and treated early in the season before insemination, so that a pregnancy can be established.
Other mares may have endocrine abnormalities and will not maintain a pregnancy past the first couple of weeks without appropriate hormone therapy. This condition can usually be diagnosed by careful examination of the ovaries at early preg test coupled with a comprehensive reproductive history.
Mares whose uterus has suffered damage either from many foals, or a single incident of retained membranes or endometritis, may have significant endometrial scarring which will limit their ability to form an adequate placenta. These mares will often appear to have a normal pregnancy, but will abort the foal when it reaches a size that can no longer be supported by the small placenta.
Such scarring can be detected by an endometrial biopsy, and the mares are ideal candidates for embryo transfer.
Maiden mares, especially those recently retired from racing, may be hard to get in foal in their first season at stud and are also more likely to reabsorb a pregnancy during the winter. Patience is required with these mares, who will often go on and have a successful career at stud.
There are many other less common problems such as ruptured pre-pubic tendon, placental detatchment, mis-shapen teats or udder, dependent oedema, pre-foaling colic, damaged cervix, lactational anoestrus, etc etc which with careful management can be circumvented to result in a healthy foal each season.