Page 968 - Small Animal Internal Medicine, 6th Edition

940 PART VIII Reproductive System Disorders

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FIG 54.10
FIG 54.8 Schematic of the canine copulatory lock.
Vaginoscopic appearance of crenulated vaginal mucosal
folds during estrus.

their estrous cycle for evaluation, or exhibit pathologic varia-
tions in their cycle. Each of these scenarios requires veteri-
nary interpretation. Considerable variation exists within the
normal range of events in the reproductive cycle. The clini-
cian must differentiate between bitches with normal estrous
cycles but unexpected patterns and those with true abnor-
malities. This usually entails monitoring a bitch during an
entire estrous cycle. Detection of individual variation within
the normal range of events in a fertile bitch can be crucial to
providing effective counseling concerning breeding manage-
ment. Evaluation of the estrous cycle for true abnormalities
is an important part of the workup of the apparently infertile
bitch (see Chapter 55).

SERUM HORMONE INTERPRETATION
FIG 54.9 Estrogen
Diestrus vaginal cytology showing parabasal and During the follicular phase of the ovarian cycle, increasing
intermediate cells and neutrophils. estrogen causes an increased turnover rate of vaginal epithe-
lial cells, resulting in the progressive cornification seen on
and prolactin secretion. Proliferation of the endometrium vaginal cytology and thickening of the vaginal wall in prepa-
and quiescence of the myometrium occur under the influ- ration for copulation with an interlocking tie (Fig. 54.10).
ence of elevated progesterone. Diestrus usually lasts 2 to 3 Also seen is progressive edema of the vaginal mucosa, seen
months in the absence of pregnancy. Parturition terminates with endoscopic examination. Estrogen assays are performed
pregnancy 64 to 66 days after the LH peak. Prolactin con- by many commercial laboratories. However, the information
centrations increase in a reciprocal fashion to falling proges- given is of little value for ovulation timing, because peak
terone at the termination of diestrus or gestation, reaching estrogen levels are variable from bitch to bitch, and even
much higher values in the pregnant state. Mammary ductal relative changes do not correlate to ovulation or the fertile
and glandular tissues increase in response to prolactin levels. period. Estrogen is best assessed by serial vaginal cytologies
and vaginoscopy. Estrogen levels do not indicate the fertile
period, because ovulation is triggered by the LH surge, not
CANINE OVULATION TIMING: an estrogen peak. Examination of the cells on the surface of
EVALUATION OF THE ESTROUS CYCLE the vaginal epithelium will give information about the stage
TO IDENTIFY THE OPTIMAL TIME of the estrous cycle, primarily by showing the presence or
TO BREED absence of an estrogen effect. It is important to always begin
ovulation timing with vaginal cytologic evaluation to confirm
Individual bitches can have nonproblematic variations of the the bitch is actually in heat and to identify the proper time
normal estrous cycle, be presented at variable times during to initiate cost-effective serial progesterone testing. Serum