Puerperium - Cow

Also see General Puerperium

Stimulus for the changes that occur in the puerperium is largely due to removal of the foetus. Hormones such as oxytocin and prostaglandin F2α are also involved. Prostaglandin F2α levels peak at 3 days postpartum and do not return to basal levels until 15 days postpartum.

Involution

• Greatest changes occur in the first few days after calving.
• Time to complete involution in beef cattle: 37-56 days
• Time to complete involution in dairy cattle: 26-52 days
• Uterine contractions continue for several days.
  • Decrease in regularity, frequency, amplitude and duration.
  • Atrophy of myofibrils over the next few days.
• After the initial rapid phase of involution, subsequent changes proceed more slowly.
• Rapid phase of involution associated with uterine discharge.
• Whole of the uterus palpable per rectum by 8-10 days postpartum.
• Speed of involution in the non-gravid horn is more variable than that of the previously gravid horn, which depends upon involvement in placentation.
• Cervix rapidly constricts, by 10-12 hours postpartum it becomes almost impossible to insert a hand through to the uterus.
  • By 96 hours, only two fingers can pass through the cervix.
  • Cervix undergoes atrophy and shrinkage due to elimination of fluid and the reduction in collagen and smooth muscle.
• A good indicator of involution is to compare the diameter of the previously gravid horn with that of the cervix.
  • At ~25 days postpartum the diameter of the cervix begins to exceed the diameter of the previously gravid horn.

Restoration of the Endometrium

The Changes that Occur in the Caruncles of the Cow during the Puerperium,Copyright L.Wilkie 2008

• During the first 7-10 days postpartum there is noticeable loss of fluid and tissue debris despite the placenta being considered non-deciduate.
  • Known as the 'second cleaning' or 'secundus'.
• Lochial discharge is normal.
  • Usually yellow/brown or red/brown.
  • Volumes vary between individuals
    • Usually ~1000ml-200ml in pluriparia
    • Rarely more than 500ml in primiparia
  • Greatest flow of lochia is 2-3 days postpartum
  • By 8 days it is reduced and becomes almost lymph-like in consistency.
  • At ~9 days it becomes blood stained.
  • By day 14-18 it has almost disappeared.
• Lochia is derived from remains of foetal fluids, blood of ruptured umbillical vessels and shreds of foetal membranes but mainly from the sloughed surfaces of uterine caruncles.
  • Slough occurs following degenerative changes and necrosis of superficial layers.
• Endometrial crypts contain remnants of chorionic villi that were detached from the rest of the allantochorion during placental separation.
• Within the first 48 hours postpartum there is early necrotic change in the sptal mass of the caruncle.
• Caruncular blood vessels become constricted and are almost occluded.
• At 5 days postpartum, necrosis proceeds rapidly.
  • Stratum Compactum becomes covered with a leukocyte-containing necrotic layer.
  • Some necrotic material sloughs and contributes to the lochia.
• Small blood vessels, mainly arterioles then protrude from the surface of the caruncle.
  • Ooze blood and cause red colouration of lochia.
• By 10 days postpartum, most necrotic caruncular tissue has sloughed and undergone liquefaction.
• Sloughing complete by day 15 postpartum.
  • Stubs of blood vessels left protruding from the Stratum Compactum.
  • Become smooth by 19 days postpartum.
• Regeneration of epithelium occurs immediately after parturition in areas that were not seriously damaged.
  • Regeneration complete in intercaruncular areas by 8 days postpartum.
• Complete re-epithelialisation of a caruncle is by day 25 onwards.
  • Mainly by centripedal growth of uterine glands.
• Caruncles are becoming smaller during this time, so at day 40-60 they are just small protrusions.
  • Larger with more melanin pigmentation and a more vascular base than in nullipara.

Return to Ovarian Cyclicity

• Anovulatory follicular waves occur periodically during gestation.
• Due to the prolonged period of inhibition ,as a result of continuous negative feedback of progesterone secreted by the corpus luteum and placenta, the pituitary is refractory postpartum.
• As a result of low/absent output of gonadotrophins, the ovary is quiescent.
• Cow is in anoestrus.
  • Prolonged in suckler and high yielding cows.
• During the postpartum phase, ovaries contain numerous large anovulatory follicles which become atretic.
  • Do not mistake for cysts!
• In the immediate postpartum period, oestrodiol and progesterone are low.
• Anterior pituitary releases FSH during the first few days postpartum.
  • With sporadic GnRH release, there is a gradual and sustained rise in plasma FSH.
  • After 7-10 days this is sufficient to cause a follicular wave.
    • Occurs at ~ 4 days in dairy cattle
    • Occurs at ~ 10 days in beef cattle
• The pituitary release of LH is slower to occur.
• Dominant follicle may emerge from the first follicular wave, but ovulation can only occur if it produces enough oestradiol to stimulate adequate LH secretion at a rate of 1 pulse per hour.
  • If this occurs, first ovulation is at 21 days in dairy and 31 days in beef cattle.
• Insulin Like Growth Factor 1 (IGF1) stimulates follicular granulosa cell aromatase activity and oestradiol synthesis.
• After ovulation, luteal phase occurs and may be of normal length.
  • Return to oestrus after 18-24 days.
• Luteal phase may be much shorter.
  • Usually because of inadequate preovulatory development of the follicle.
    • May become leutenised in the absence of ovulation or leutinisation of the CL is commonly inadequate.
• First sign of oestrus not always true indicator of onset of ovarian cyclicity.
  • Because the central nervous system (CNS) requires prior exposure to prgesterone to elicit behavioural signs.
    • Onset can be determined by assay of milk showing elevated progesterone levels.
• Adrenal Cortex also exerts influence over ovarian cyclicity.
  • Adrenocorticotrophic hormone (ACTH) supresses LH secretion.
  • Stimulation of the teats and milk ejection causes a rise in glucocorticoids.
    • Delays return to ovarian cyclicity.

Bacterial Elimination

• At calving and immediately postpartum, the vulva is relaxed and the cervix is dilated.
• Bacteria can gain entry via the vagina and travel to the uterus.
• Blood, cell debris and sloughed caruncular tissue provide an ideal environment for bacterial growth.
• However, in most cases bacteria do not colonise the uterus to cause metritis/endometritis.
• Bacteria is eliminated by:
  • Phagocytosis by migrating leukocytes
  • Persistent uterine contractions
  • Sloughing of caruncular tissue
  • Uterine secretions
• Early return to cyclicity is important, because under the influence of oestrogen, the uterus is more resistant to bacteria.