Parturition

Question 1

What has to happen before parturition can occur?

Answer 1

• Final maturation of fetus
• Termination of pregnancy
• Expansion of birth canal
• Initiation of uterine contractions
• Maternal behavior favorable to survival of young
• Synthesis of milk
• ejection of milk (at proper times)

Question 2

What is the trigger for Parturition?

Answer 2

• Fetus determines the onset of parturition via attainment of functional hypothalamic-pituitary-adrenal axis (HPAA)
  
  • Fetal hypothalamus can produce CRF
  • Fetal anterior pituitary can produce ACTH
  • Fetal adrenal gland can produce cortisol
• Target is placenta
• Increasing estrogen levels up-regulate oxytocin receptors in the uterus
• Oxytocin production is increased (post pit and CL)
• PGF_2a production by uterus is increased
• Increasing estrogen lowers threshold potential for electrical stimulation of uterine smooth muscle
• Ca⁺⁺ influx initiates uterine contractions
• Abdominal contractions aid in forcing fetus into pelvic canal
• Ferguson reflex - pressure on the cervix as the fetus enters the pelvic canal stimulates the release of oxytocin from the posterior pituitary
• A posterior feedback cycle between increasing contractions and increasing oxytocin lead to expulsion of the fetus

Question 3

What hormonal changes happen during parturition?

Answer 3

• Increasing estrogen (placental origin)
• Increasing prolactin and placental lactogen
• Decreasing progesterone (maternal P₄ falls rapidly last week of gestation - falling to baseline levels)
• Increased relaxin from CL and placenta
• Increased PGF_2a from endometrium
• Increased oxytocin (from CL and placenta)
• Increased oxytocin receptors in uterus
• PGF and oxytosin begin to stimulate uterine muscle contractions (estrogen promotes)
• PGF, estrogen, and relaxin cause softening of cervix and relaxation of pelvic ligaments

Question 4

What happens Post-parturition?

Answer 4

• Uterine involution
  
  • requires 20-40 days (species variation)
  • Does not appear to play a major role in post-partum infertility
    
    • negative effects of the post-partum uterine environment on fertility end earlier than other negative effects on fertility (i.e. suppressed hypothalamic-pituitary axis)
• Lochia - Normal discharge following parturition
  
  • present for up tot 3-4 weeks
  • red, green, black (species variation)
  • Non-odorous
  • Contains bits of mucus and placenta
• Expel fetal membranes
  
  • should be expelled w/n a few hours
  • can be a medical emergency
• Post partum complications
  
  • Clinical signs- depression, fever, etc
    
    • malodorous discharge
• Recovery of hypothalamic-pituitary function
  
  • GnRH pulse generator does not function post-partum due to:
    
    • Prolonged P4 elevation
    • Nutritional insufficiency
    • Suckling effect
      
      • minimal effect on elephant, mare, and dairy cows
      • Rodents and marsupials - ovulate soon after parturition, but embryo goes into diapause until lactation is over
      • Porcine - very strong (no cycles)
      • Anestrus in early lactation - beef cow and humans
  • Mare resumes cycling shortly after parturition (foal heat) 1-2 wks post foaling
• Initiate lactation
  
  • Primary hormones involved:
    
    • Mammary gland development - estrogen, prolactin (placental lactogen, and growth hormone
      
      • increase near puberty and again in late gestation
    • Initiation of lactation - progesterone decreases, cortisol, estrogen, and prolactin increase
• Maintain lactation
  
  • Growth hormone is the main hormone
  • Oxytocin required for milk let-down

Question 5

What are some post-parturition complications?

Answer 5

• Uterine prolapse
• Retained fetal membranes
• Mastitis
• Metritis
• Hypocalcemia
• Lactation failure

Question 6

What is Uterine prolapse? causes?

Answer 6

• Prolapse of all or part of the uterus
• Associated with prolonged or difficult birth
• Associated with hypocalcemia
• Most common in cattle and sheep
• Less common in dogs, cats, horses
• Medical emergency
  
  • hypovolemic shock
  • hemorrhage
  • Thromboembolism
  • Infection/septicemia

Question 7

What causes retained fetal membranes? How serious is this?

Answer 7

• Failure to expel the placenta(s) after parturition
  
  • Non life-threatening in cattle
  • Serious in horses
• Causes:
  
  • Metritis - uterine infection
  • Alteration in timing of hormonal changes leading to parturition (abortion)
  • Dietary mineral imbalances
  • Unknown
• Complications:
  
  • metritis
  • septicemia
  • laminitis (equine)

Question 8

What is metritis?

Answer 8

• Involves the endometrium, uterine glandular tissue, and underlying muscle layer
• Differentiated from endometritis - (only involves endometrium & glandular tissue)
• Initiated by viral, bacterial, or protozoal insult
• Sequelae
  
  • Milk
  • Severe illness / Death

Question 9

What is mastitis? how serious is it?

Answer 9

• Bacterial infection of one or more mammary glands
• Mild cases are asymptomatic
• Can be severe
  
  • clinical signs - hot, inflamed, painful gland
  • systemic illness / death
• Can occur in pseudopregnant bitches and queens

Question 10

What is hypocalcemia? causes? seriousness?

Answer 10

• Cow & Mare: metabolic disease that occurs within a few days of parturition
  
  • Occurs prior to peak lactation
  • Blood calcium levels are supposed to be tightly controlled by hormonal regulatory system (parathyroid hormone, Vit D, calcium binding protein
• Bitch: occurs at peak lactation (small breeds)
  
  • associated with large litter at peak lactation
  • calcium drain due to high lactation level
• Clinical signs:
  
  • Hyperexcitability (restlessness)
  • Muscle fasciculations
  • Muscle paresis
  • Tachycardia/Bradycardia
• Treatment:
  
  • IV calcium gluconate
    
    • auscultate heart - stone heart
  • Oral calcium (canine)
  • Correct pre-disposing causes (cow/mare)

Question 11

What is lactation failure? causes? seriousness?

Answer 11

• Low (or absent) milk production due to a number of factors:
  
  • Maternal starvation
  • Damaged mammary glands - mastitis
  • Endophyte-infected fescue (equine)
• Delayed onset of lactation
  
  • more common following first gestation
  • Can occur in multiparous females
• Invtervention
  
  • feed the young
  • keep the dam calm - reduce stress
  • No hormonal intervention proven to be effective
  • Most will initiate lactation w/n days