BACK TO REPRODUCTIVE SYSTEM BACK TO PARTURITION

Why Control Timing of Parturition?

Herds

Improves supervision to ensure the farmer can be around at the time of parturition.
Reduces the incidence of parturition at night/weekends which is socially undesirable.
Aids cross fostering between litters.
Tightens the calving interval in cattle.

Individuals

Maternal emergrncy such as abnormal foetal position, bone fracture of the pelvis etc.
Foetal abnormality, or an oversized foetus.

Disadvantages of Parturition Induction

Timing may not be absolutely perfect, there is considerable variation in the timing of drug action and effect.
Premature delivery of small, immature offspring.
Increased incidence of retained placenta.
Pharmacological induction can only be used commercially in cattle and pigs. Induction in other species is used only to overcome birth associated problems.

Requirements for Parturition Induction

You must ensure the foetus is appropriately developed before inducing parturition. The lungs must be mature to enable survival. Naturally maturation of the lungs is induced by foetal cortisol, so it may be useful to administer glucocorticoids to artificially mature the lungs.

  Prostaglandin F2α: Cervical dilation
  Prostaglandin F2α and Oxytocin: Uterine contractions
  Oxytocin: delivery of the Placenta

Oxytocin and Prostaglandin F2α both signal by the Gαq -> IP3 + DAG pathway to raise intracellular calcium , so are able to effect each other in the Fergusson reflex.
COX II increases during labour, so prostaglandins will form as long as arachidonic acid is available.

Drugs Influencing Uterine Activity

Ecbolic Drugs

Induce parturition by uterine activation.

Ergot Alkaloids

Induce contraction
Vasoconstrictors
Not used in the UK
Ergonavine taken off the market, Methergine is the only derivative in use.

PGF2α Analogues

Dinoprost
Clonprosterol
Exert action over a long period of time.

Oxytocin

Used in conjuction with Oestradiol Benzoate
- Oestradiol induces oxytocin receoptor upregulation on the endometrium.
- Inhibits uterine activity, but sensitizes the uterus to oxytocin.

Tocolytic Drugs

Delay parturition by relaxation of the uterine myometrium.

Progesterone

Slow acting steroid through nuclear receptors.
Not useful in emergency situations.

Relaxin

Rapidly acting peptide hormone
Essential in farrowing sows

Myometrial Innervation and Manipulation

The autonomic nervous system is not important in normal labour, since uterine contractions are controlled by the neuroendocrine release of oxytocin. However, the autonomic nervous system can be used to control parturition pharmacologically by changing cAMP levels which effects the myometrium.

Sympathetic

α Adrenoceptors

Induce contractions
Agonists induce parturition
Antagonists delay parturition

β Adrenoceptors

Progesterone increases the number of β Adrenoceptors
Inhibit contractions
Agonists delay parturition e.g. Clenbuterol
Antagonists induce parturition e.g. Carazolol

Parasympathetic

Acetylcholine inhibits contractions

Induction of Parturition

Cow

To Induce Parturition

Corticosteroids

Mimic foetal cortisol to remove the progesterone block by upregulating enzymes that will increase the oestrogen:progesterone ratio (for more information see endocrinology of parturition).
Short Acting: apply 2-3 days before the due date (270+ days gestation). Complications include retained placenta and stillbirth.
Medium-Long Acting: apply 2-3 weeks before the due date. Administration after 260 days will cause no advance of the calving date. Administration before 260 days will cause neonatal mortality. Thus use of these corticosteroids is reliant upon accurate record keeping by the farmer so that exact dates are known.

Corticosteroid & PGF2α Analogue

Has the additional benefit of acting to dilate and soften the cervix to facillitate delivery.

Parturition Pharmacological Manipulation - Anatomy & Physiology

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