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Methods of induction of parturition
There has been periodic interest over the last two decades in the induction of
parturition in cattle. However, the procedure has only really gained wide
acceptance in New Zealand. This is mainly due to the fact that dairying in
New Zealand is highly seasonal and lactation should coincide with
maximum pasture availability. In the UK and other countries, the technique
has not been popular because of the high prevalence of retained placenta,
and reports of poor calf viability, reduced milk yield and reduced fertility.
However, with the increased use of larger bulls in the UK it can be
advantageous to advance the timing of parturition in order to minimize
problems of dystocia due to fetal oversize.Also there are circumstances in
which it is desirable to advance the time of calving to coincide with seasonal
payments.
Corticosteroids
There is now a considerable body of information on the effects of
corticosteroids on the pregnant cow. Parturition can be induced quite reliably
from about day 255 of pregnancy onwards by a single injection of a
synthetic glucocorticoid such as dexamethasone, betamethasone or
flumethasone. It is assumed that such therapy simulates the effect of the fetal
adrenal cortex. A study was carried out on the use of dexamethasone
undecanoate to induce parturition in dairy cows in the UK. Cows were
induced with 7.5mg dexamethasone undecanoate (Dectan: Hoechst) either
14 or 5 days before term or left as untreated controls.
Dexamethasone treatment reduced gestation length by 10.8 and 4.3 days
(significant reductions) when given 14 or 5 days respectively before the
expected date of calving. Cows induced 5 days early calved sooner after
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Obstetric …………………………………………………………………………………dr.hella J. Al-Fatlawy
injection (range 22–71 hours) than those induced 14 days early (range 40–
190 hours). Induction of calving 14 days early resulted in a significant
decrease in calf liveweight of 3.2kg at one day of age. However, there was
no significant difference in calf liveweights of cows induced 5 days early
and their controls.
There were no significant differences in calving difficulty between
induced and control cows. However, cows induced 14 days early tended to
pose more difficulty in calving. These difficulties appear to have been
related mainly to inadequate pelvic dilatation at the induced parturition.
Dexamethasone treatment caused a significant increase in the time that the
placenta was retained in both induced groups, although this was longer in the
cows treated 14 days early (mean 3.5 days) than those treated 5 days early
(2.5 days). Of the 17 cows induced 14 days early, 14 retained the placenta
for 4 days whereas only 1/17 control cows retained the placenta for more
than 12 hours. In the group induced 5 days early the problem was less
marked, with 5/13 cows retaining the placenta for 4 days.The additional
veterinary cost (excluding dexamethasone treatment) for cows induced 14
days early was £14.50 per cow and the cost differential for those induced 5
days early was £1 per cow. Calf survival over all treatment groups was 95%,
with only three calves dying at birth and which were unrelated to any
treatment group. There was no difference in subsequent calving to first
service intervals between treated and control cows. Retained placenta
possibly leading to endometritis was clearly associated with subsequent
subfertility, particularly in the 14-day group. However, induction did not
significantly affect either milk yield or quality.
cortisol profiles at parturition might be altered after induction of parturition
with dexamethasone, leading in turn to retained fetal membranes. Induction
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Obstetric …………………………………………………………………………………dr.hella J. Al-Fatlawy
of parturition using corticosteroids is now an essential part of management
in many New Zealand dairy herds and considerable experience of the
technique has been gained. Both short- and longacting formulations have
been used. Short-acting formulations, generally in the form of a soluble ester
of the steroid, usually result in parturition 2–3 days later. Although the
calves are usually viable, this method has been associated with a high rate of
retention of the fetal membranes. The use of longer-acting corticosteroid
formulations, for example a concentrated suspension of ‘betamethasone
alcohol’ (MacDiarmid, 1979), resulted in a more protracted response, up to
two weeks in some cases, and a high incidence of calf mortality. In
conclusion, parturition can be induced with dexamethasone undecanoate as
early as 14 days prepartum with no adverse effects on calf viability or milk
yield. However, an increased incidence of retained placenta may lead to
increased veterinary costs and subfertility which may or may not be
acceptable depending on the indications for induction. Induction nearer the
time of parturition is unlikely to be associated with adverse side effects.
Prostaglandins
Prostaglandins, both PGF2a and synthetic analogues, may be used to induce
parturition in cows, although treatment before day 270 of gestation is not
recommended.
Parturition usually occurs between one and eight days after injection but at
an average of three days. There is likely to be a higher incidence of calving
difficulty, stillbirth and retained placenta, as reported, e.g., by Kornmatitsuk
et al. (2002) who were also concerned with fetal well-being. A study under
UK conditions (Murray et al., 1984) used a treatment regimen whereby cows
were injected with 20 mg dexamethasone and those that had not calved 10
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Obstetric …………………………………………………………………………………dr.hella J. Al-Fatlawy
days later received an injection of 0.5 mg cloprostenol (an analogue of
PGF2a. Although there was a high incidence of retained placenta, this did
not affect subsequent reproductive performance. It was concluded that
provided management was organized adequately to supervise parturition and
take care of the neonates, then this procedure could be carried out to
advantage. A characteristic of early studies on the pharmacological
induction of parturition was the high rate of calf mortality and post-calving
problems, particularly retained placenta. An important determinant of the
incidence of retained placenta appears to be the oestrogen status of the cow
at the time of induction.
As discussed above, oestrogen concentrations rise during late pregnancy,
hence the oestrogen status may simply be a reflection of the proximity of
term or ‘readiness to calve’. From an exhaustive review of the available
literature, First (1979) concluded that if induction is carried out when
oestrogen levels are elevated, both glucocorticoids and prostaglandins are
effective. However, glucocorticoids were the most appropriate treatment if
induction was to be attempted earlier. The earlier that interference is
attempted the higher the probability of calf mortality, retained placenta and
other related problems.
Delay of parturition
It is now possible to delay parturition for several hours with pharmacological
treatments. This is usually carried out so that supervision for calving can be
more conveniently and readily available. Injection of the potent adrenergic
drug clenbuterol inhibits myometrial contractions, thus slowing down the
first stage of labour. However, if treatment is started after second-stage
labour has already commenced, it would have little effect.
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