Page 515 - Anatomy and Physiology of Farm Animals, 8th Edition

500 / Anatomy and Physiology of Farm Animals

extent in the body of the uterus, while a calf birth; in some cases, birthing is not possi-
ble without assistance. In general, from the
is carried almost entirely in one horn of the
VetBooks.ir uterus. Presentation of a foal is essentially onset of labor, cows should calve within 8
hours, ewes should lamb within 2 hours,
the same as that of a calf. With pigs and
dogs, the young are carried in both horns of and mares should foal within 2 to 3 hours.
the uterus and may be presented either cra- Sows should average one offspring per
nially or caudally with equal facility. hour until farrowing (i.e., birthing of a lit-
In species that typically have a single ter) is complete.
offspring, the placenta, or afterbirth, is In large animals (cow, mare, and ewe),
delivered soon after birth, but it may improper fetal presentation is a common
accompany the fetus or, rarely, precede it. cause of dystocia, and typically with abnor-
In the litter‐bearing sow, the placenta for mal positioning of the limbs or head (e.g.,
each fetus is typically delivered still head rotated up and ventrum of neck pre-
attached to the fetus and may completely sented or head rotated down and dorsum
surround the fetus. In these cases, immedi- of neck presented). Correction of such a
ate removal of the placenta from the nos- presentation may be necessary for delivery
trils of the newborn is essential for life; of the fetus. Correction usually entails
usually the sow does it. A placenta is con- repelling the fetus into the uterus away
sidered to be retained pathologically if an from the pelvic inlet so that the fetus can
abnormally long time elapses between be manipulated and the position of its
birth of the young and delivery of the pla- limbs and head changed.
centa. The placenta of the cow and ewe Excessive size of the fetus relative to
should be delivered within 24 hours, and the size of the birth canal of the dam
the placenta of the mare should be deliv- may also produce dystocia. This is a
ered within 2 to 3 hours. common cause of dystocia in first‐calf
Retention of the placenta is a signifi- heifers and in relatively small cows
cant problem in all mammals. The inci- mated with much larger bulls. Excessive
dence seems to be higher in cattle than fetal size may also produce problems in
other species and higher in dairy than in ewes with single lambs and sows with
beef breeds. Manual removal of a small litters. Even though the presenta-
retained placenta has been a common tion may be normal in these cases, exces-
method of treatment, but more conserv- sive traction may be required to deliver
ative treatment (i.e., no manual removal, the newborn, and this may damage both
with antibiotics to prevent infection) is the fetus and the dam.
also advocated, and is supported by A cesarean section (surgical removal of
research studies. the fetus) may be necessary in some cases
of dystocia. Successful surgeries produce a
viable fetus and preserve the reproductive
Dystocia capacity of the dam. An embryotomy
(surgical dismemberment of the fetus to
Normal parturition with no complications permit its passage through the birth canal)
is by far the most common occurrence in may be necessary in some cases to save the
domestic animals. Dystocia is difficult life of the dam.