The mares must wear rubber urine-collection bags at all times which causes chafing and lesions. For most of their 11-month pregnancies, these horses are confined to stalls so small that they cannot turn around or take more than one step in any direction.

Pregnant Mares on a “Pee Line” in Manitoba.
The name Premarin® spells out in its name what it is made from —
PREgant MAres uRINe.
Pfizer’s Premarin® family of hormone replacement therapy drugs of
today includes not only Premarin®, but also similarly manufactured
pharmaceuticals — marketed at various times — under the names
Prempro®, Premphase®, Provera® and later Aprela® (originally called
Duavee or Duavive before its release). Add to the list Premplus
which was developed by Wyeth until Pfizer came along and made them
part of its empire.
Premarin®, Prempro® and Premphase® are typically prescribed to women
to help reduce symptoms of menopause such as hot flashes and vaginal
dryness.
Provera®, in combination with an estrogen-containing medicine, is
used to relieve symptoms of menopause in women with an intact
uterus. Provera® is also used to protect the lining of the uterus
while the estrogens relieve the symptoms of menopause.
....
Please read the ENTIRE ARTICLE HERE (PDF)