Puerperium - Sow

Also see General Puerperium

Changes of the puerperium must occur rapidly, with a return to the normal pregravid state, so that pregnancy can occur as quickly as possible after weaning.

Involution

• Rapid initial uterine shrinkage in the first 5 days postpartum.
• After day 6, most uterine weight loss is due to changes in the myometrium:
  • Reduction in cell size
  • Reduction in cell numbers
  • Reduction in the amount of connective tissue
• Uniform decrease in thickness of the endometrium and myometrium.
• Complete by 28 days
• In early-weaned sows, uterine involution is slower
• The morphology and physiology of the genital tract may not be optimal for fertilization and blastocyst implantation in sows weaned at farrowing or shortly after, resulting in a reduced rate of gestation or a reduced litter size
• The fastest and most reliable way to monitor uterine involution is to use ultrasonography
• Prolonged uterine pathologies, including retention of fetal membranes or endometritis, can negatively impact the duration of uterine involution

Restoration of the Endometrium

• During puerperium the uterus returns to its nongravid size and the endometrium is restored to provide a suitable environment for the establishment of a new pregnancy
• This uterine involution is generally completed within 3 weeks of farrowing.
• 1 day after farrowing, the uterine epithelium is low columnar or cuboidal.
  • Extensive folding present during pregnancy
• At 7 days, epithelial cells are very low and flattened, showing signs of degenerative change.
  • Also signs of cell division, responsible for regeneration of the epithelium.
• Complete and capable of sustaining another pregnancy after 21 days.
• An delayed restoration of endometrium and uterine involution can have a negative effect on sow reproduction.

Return to Ovarian Cyclicity

• Suckling and weaning have an effect on return to ovarian cyclicty (ovarian rebound) and other puerperial changes in the tract.
• Mostly no return to oestrus and no ovulation until piglets are removed.
• Time to first ovulation can be shortened by temporary removal of the whole litter for varying periods during the day (partial weaning), or permanent removal of part of the litter.
• Weaning pigs immediately after farrowing or within three weeks of delivery results in higher incidence of anestrus and a longer weaning-to-estrus interval, ovulation failure, or a reduced litter size
• Female pigs that fail to ovulate either show follicular regression or develop cystic ovarian diseases.
• Rapid regression of corpora lutea of pregnancy, with cellular degeneration occuring by 3 days postpartum.
• By day 7 postpartum, corpora lutea are mainly connective tissue.
• Follicular activity occurs during suckling, which is sometimes associated with behavioural oestrus shortly after farrowing.
  • No ovulation, follicles become atretic
• Preovulatory surge of LH within 7 days of weaning.
• Anoestrus and ovarian cysts in early weaned pigs may be due to the lack of a preovulatory LH surge
• Most of the sows resume cyclicity within a normal weaning-to-oestrus interval of less than 7 days if they are weaned after 3 weeks of farrowing
• Prolactin concentrations are high during lactation but decline rapidly to basal levels within hours after weaning.
• Follicular growth and ovulation are supressed during lactation due to supressed LH secretion.
• FSH concentrations rise after weaning.