Pharmacological control of parturition

Question 1

What are the three stages of parturition?

Answer 1

1. Onset of myometrial contractions
2. Expelling of the fetus
3. Expelling of the placenta

Question 2

Describe what occurs during the onset of myometrial contractions.

Answer 2

Relaxin is produced by either the placenta (horse, dogs and cats) or CL (in ruminants and sows). This causes relaxation of vulval tissues, perineal tissues and pubic symphisys. Fetus produces cortisol which causes a decline in progesterone in the mother by negative feedback on the hypothalamus and anterior pituitary. This leads to elevated oestrogen and increased prostaglandin.

Question 3

What occurs during the expelling of fetus stage?

Answer 3

A neurohormonal reflex causing oxytocin release – due to the fetus putting pressure on the cervix. Oxytocin increases contractions

Question 4

What occurs during the expelling of the placenta phase?

Answer 4

Myometrial contractions become more frequent but decrease in amplitude. There is no/less pressure on the cervix now so there is less oxytocin. Abdominal contractions also stop after fetal expulsion.

Question 5

What are the indicators for premature induction in the horse?

Answer 5

• ensures parturtion occurs in the presence of skilled assistance
• disease/illnesses of the mare

Question 6

What are the indication for premature induction in cattle?

Answer 6

• Advancing the time of calving to coincide with the availability of suitable pasture for milk production
• Ensuring that cows calve at predeterminded time when skilled assistance is available so that prompt attention can be given – reduces calf mortality and injury to the cow
• Reducing the birth weight of the calf by shortening the length of gestation – reduces likelihood of dystocia
• In diseased or injured cows where the termination of pregnancy will alleviate the condition or where a live calf can be obtained before slaughter

Question 7

What are the indications for premature induction in the sow?

Answer 7

To shorten farrowing length and thus to prevent inertia and rate of stillbirths

Question 8

What are the indications for premature induction in the ewe?

Answer 8

To allow ewes to lamb over a relatively short period of time in a single batch.

Question 9

What is dexamethasone indicated in?

Answer 9

Induction of parturition in cattle

Question 10

What are the complications of inducing early parturition in cattle?

Answer 10

• Not always effective
• Birth weight of calf is lower than it would have been at term
• High incidence pf retained fetal membranes when short acting preparations are used
• Milk yield is initially affected, with a delay is reaching peach lactation
• Subsequent fertility is fairly normal although the calving to conception internval and the number of services per concentpion are slightly increased in those cows that retain their fetal membranes
• There is a reduction in the quality and quanity of colostral immunoglobulins, especially after the use of slow release corticosteroid preparations, although it is unlikely that the calf will not acquire an adequate passive immunity

Question 11

What drugs can be used to delay parturition?

Answer 11

B-adrenergic agents