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REPRODUCTION
Topic: Medetomidine in high risk anaesthesia, such
as
caesarian section in the bitch
pregnancy, the endometrium will secrete prostaglandin-F2α
which results in luteolysis of the CL and resumption of cy-
clicity. In species that do not have maternal recognition of
pregnancy, for example the dog, then the CL will continue
for its normal lifespan of 70-90 days before regressing.
Controlled Sedation
In the male, there is no surge centre equivalent of that of
the female animal. Instead, frequent, intermittent release of
GnRH from the tonic centre, causes an equivalent release of
LH from the adenohypophysis. The LH acts on the Leydig
(Interstitial) cells within the testes to produce testosterone
which is required for spermatogenesis. This episodic release
of LH is important to prevent sustained release of testoster-
one which would result in down-regulation of the GnRH/LH
feedback system. In the Sertoli cells, under the influence of
FSH, testosterone is converted to dihydro-testosterone and
oestradiol. Testosterone, dihydro-testosterone and oestradi-
ol all exert a negative feedback effect on the hypothalamus
and the adenohypophysis. The Sertoli cells also secrete in-
hibin, which further suppresses the release of FSH. The im-
portance of inhibin and suppressed FSH release in the male
is currently unclear.
Date: 1 August 2017
Time: 12pm or 8pm
Speaker: Dr Kurt De Cramer
LH assays
In bitches, an in house LH assay (WITNESS® LH kit, availa-
ble on request from Zoetis South Africa) can be used during
oestrus monitoring to determine the pre-ovulatory LH surge
which occurs about 48 hours prior to ovulation. 1,2 The LH-
surge only lasts 24-48 hours, therefore twice daily monitor-
ing of LH levels may be indicated to identify the LH surge 3,4 .
In bitches, oocytes are ovulated as primary oocytes, which
still need to undergo further maturation and expulsion of the
polar body before they become secondary oocytes capable
of being fertilized. This maturation process take roughly 48
hours.
Therefore, the optimal time for insemination when unlim-
ited matings or AI is available is roughly 4 days after detec-
tion of the LH surge and then every 48 hours until the bitch
goes into dioestrus. With frozen semen which has a limited
lifespan of roughly 12-24 hours or when limited access to the
stud dog dictates only one mating, then the optimal day for
insemination is on day 5 or 6 post LH surge. The LH-surge is
very useful for monitoring the length of gestation in the bitch
as parturition will occur 65 +/- 1 day post LH-surge. Once
a bitch or a queen has undergone an ovariohysterectomy/
ovariectomy, the removal of the gonads and, by extension,
the gonadal steroids, removes the negative feedback on the
hypothalamus and the adenohypophysis. In one study, basal
LH levels in ovariectomised bitches (n=6) were significantly
higher (20.2 ± 3.6 μg/L) compared to unspayed bitches in
anoestrus (n=6, 0.64 ± 0.04 μg/L).
A once off LH assay to determine whether or not a
bitch has been ovariectomised has excellent sensitivi-
ty (98%) but moderate specificity (78%) meaning that a
single low LH assay confirms that a bitch is intact, but
that that a single high LH assay does not confirm that
she is ovarectomised. 13 Serial LH assays can be used
to confirm her ovariectomised status.
Predictable Recovery
Progesterone assays
In dogs, a much more practical method to monitor
the oestrus cycle and determine the optimum time
to breed a bitch is the use of progesterone assays.
In bitches, granulosa cell production of oestradiol
switches to progesterone production just prior to the
pre-ovulatory LH surge. Various studies have estab-
lished that the progesterone equivalent at the time of
the LH surge is about 6 nmol/L 14,15 and at the time of
ovulation, progesterone levels reach > 16 nmol/L and
these results can be used to determine the optimal
time to breed a bitch. With frozen semen AI, insemi-
nations are performed 5 and/or 6 days after the rise in
progesterone indicating the LH surge has occurred .
Semi-quantitative in-house progesterone kits (Pre-
Mate™- Camelot Farms, College Station, TX, TAR-
GET™ Canine Ovulation Timing Test Kit - BioMetallics,
Princeton, NJ) which show a colour change depend-
ing on the plasma progesterone concentration are
not accurate and many laboratories use human rea-
gents which may produce erroneous results. For ac-
curate progesterone results a qualitative radioimmu-
noassay (RIA) or a chemiluminescent immunoassay
must be used. Currently, Idexx South Africa send all
animal samples for p rogesterone to the Reproduction
Laboratory at Onderstepoort* for testing and interpre-
tation.
In bitches exhibiting silent oestrous cycles where
there are very few external signs of heat or where the
bitch is not reacting appropriately to the male, pro-
gesterone may be used to monitor her cycle and de-
termine the best time for AI or mating.
In bitches with a history of primary anoestrus (bitch
>24 months of age without showing signs of oestrus),
monthly vaginal cytology and progesterone assays
can used to determine whether a bitch is beginning
pro-oestrus or whether she is exhibiting a silent heat
without external signs of oestrus. In older bitches ex-
hibiting signs of secondary anoestrus (>12 months
between successive oestrous cycles , serum proges-
Webinar sponsored by Zoetis South Africa (Pty) Ltd., Co. Reg. No.: 2012/001825/07, 6th Floor, North Wing, 90 Rivonia Road, Sandton, 2196.
PO Box 783720, Sandton, 2146, South Africa. Tel.: +27 11 245 3300 or 0860 ZOETIS (0860 963847). www.zoetis.co.za
25/07, 6th Floor, North Wing, 90 Rivonia Road, Sandton, 2196.
ZOETIS (0860 963847). www.zoetis.co.za
TD/IN/DDA
Issue 04 | AUGUST 2017 | 9