Parturition Pharmacological Manipulation - Anatomy & Physiology
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
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