Gestation in Swine
| Details | Piggy Sow | Ultrasonography | Housing | Limit Feeding | Fetal skeleton |
On days 9 to 12, intrauterine migration of embryos occurs to equalize the number of embryos per horn.
On days 12 to 16, rapid elongation of the blastocyst occurs, from 4mm to 1 meter.
Estrogen is luteotrophic in swine and production by the blastocyst begins on day 12.
Exocrine release of PGF-2a into the uterine lumen instead of the uterine vein, under estrogen influence, prevents luteolysis. The corpora lutea are required throughout pregnancy and luteolysis at any stage of gestation will cause resorption or abortion.
A minimum of 4 embryos are required to maintain pregnancy. If fewer than 4 embryos are present in the uterus, luteolysis occurs, probably due to insufficient estrogen production by the trophoblasts to prevent release of prostaglandin.
If all pregnancies occur in one horn (like in segmental aplasia), luteolysis occurs and the pregancy is terminated.
Attachment of the diffuse, microcotyledonary epithelialchorial placenta occurs at days 15-17.
Immuno-competence in piglets occurs by 60 days gestation.
"Piggy Sows" Pregnancy detection is usually done by observation for failure to return to estrus 17-21 days following mating. Then, at around 3 months gestation, the sow will take on a "piggy" appearance or pot-bellied abdomen and enlarged udder.
This piggy sow has the typical pot-bellied appearance of a pregnant pig. Note that her udder is not yet filled with milk (it will fill at about 24 hours pre-partum.) Non-pregnant pigs should have a svelte waistline.
Ultrasonography (A Mode) is another commonly used method for pregnancy detection which is best used at 25 to 70 days post mating. False positives can be cause by the urinary bladder, pyometra, or a dead litter. The test is more useful for detection of nonpregnant rather than pregnant sows.
This herdsman is pushing the ultrasound detector into the sow's flank in order to have the ultrasound beam bounce back from the pregnant uterus (which is a fluid-filled mass.) The urinary bladder creates a common false positive in unskilled hands.
Housing types for the sows include: pasture, pens, and stalls.
Limit feeding is typical to constrain sow size. Gestational feed intake which is too high leads to a low lactational feed intake. It is thought that in the wild, the sows overeat and build reserves for lactation. During lactation, they do not eat, but just feed piglets. Perhaps this strategy helps protect piglets from danger. Unfortunately, in modern swine farms, we know that low lactational feed intake leads to lower milk output and slowed piglet growth. Therefore, sow feed intake must be limited during gestation to prevent the dip in milk production during lactation.
The fetal skeleton begins development around day 30. This is important because, if the fetuses die before age 35 days, they will be resorbed. If they die after, they will become mummified because the bone calcium cannot be resorbed. !A clever herd manager or veterinarian can tell when a disease process has affected a herd based on this information.
Copyright ©1997 by the University of Pennsylvania School of Veterinary Medicine
Faculty: Dr. Paul Pitcher
Student: Sandra Springer,'99