Page 970 - Small Animal Internal Medicine, 6th Edition

942 PART VIII Reproductive System Disorders

maturation (~24-48 hours after the LH surge), and the fertile more than 30.0 ng/mL during the fertile period. However, if
period (~3-6 days after the LH surge) can be obtained. It is accurate serial quantitative progesterone assays are obtained,
VetBooks.ir the least expensive way to perform ovulation timing, albeit the LH surge may be estimated as the first day a distinct
increase in progesterone concentration is seen, commonly
retrospective. It can also be very useful if evaluation of ges-
tational age becomes important, because parturition occurs
as actual identification of the LH surge by use of an LH
56 to 58 days from the diestrual shift. between 1.5 and 4.0 ng/mL. This will not be as accurate
assay, but estimation of the LH surge using progesterone
Luteinizing Hormone results is still very useful and often more widely available,
At the end of the follicular phase of the estrous cycle, a less costly, and more convenient. When timing breedings
marked increase in LH over its usual basal values occurs over using semiquantitative in-clinic progesterone assays, only a
a 24- to 48-hour period, followed by a return to baseline. range of progesterone is obtained, not an actual number,
This surge in LH is thought to take place in response to the making it difficult to accurately identify the exact day of
decline in estrogen/progesterone ratio that occurs as estro- the initial rise in progesterone or the true fertile period.
gen levels decrease and progesterone rises. The LH surge Technical problems with these kits have occurred, so these
triggers ovulation and thus makes it the central endocrino- assays should only be used for ovulation timing for routine
logic event in the reproductive cycle of the bitch, with all natural or fresh artificial breedings involving fertile dogs,
events after being consistent between bitches. Daily serial where a wider margin of error is acceptable. A safe rule of
measurement of LH to identify the exact date of the LH surge thumb to follow is that when kit testing indicates proges-
is therefore the most accurate diagnostic tool for timing terone has risen above 2.0 ng/mL, breeding should begin.
breedings. Affordable semiquantitative in-house kits (Status- Optimal ovulation timing for chilled semen breedings,
LH [Synbiotics/Pfizer/Zoetis]) are available for measuring breedings involving subfertile bitches or stud dogs, or frozen
serum LH levels in the dog, identifying the preovulatory LH semen breedings should utilize quantitative progesterone
surge and thus the time of ovulation and the true fertile assays from commercial laboratories; the cost difference is
period. LH testing is the most accurate means of ovulation minimal. Regardless of which assay is used, an additional
timing and should be considered the gold standard. However, test should always be performed 2 to 4 days after the initial
samples must be drawn daily at about the same time of day, rise is detected to indicate that the cycle has progressed as
because the LH surge may have a duration of only 24 hours expected, functional corpora lutea have formed, and ovula-
in many bitches and could be missed if even one day was tion has occurred; progesterone concentration should be over
skipped. Commercially available LH kits can be subject to 5.0 ng/mL.
variable operator interpretation, so the same person should Vaginoscopy may be performed throughout the cycle as
run the tests if possible. Serum progesterone testing must an adjunct to vaginal cytologic analysis and hormonal assays,
always be done in concert with LH testing in the event that especially when evaluating an unusual cycle or if only one
the LH surge is missed. breeding is planned. Vaginoscopy is especially useful if a
bitch is initially presented late, after the day of the LH surge,
Progesterone with greater than 90% superficial cells on vaginal cytology
Unique to the bitch, progesterone begins to rise at approxi- and progesterone of above 3.0 ng/mL. Maximal crenulation
mately the time of the LH surge (actually before ovulation), (puckering of the vaginal mucosa) occurs when the ova are
enabling indirect detection of the LH surge. Rising proges- mature and most fertilizable, and can be judged quickly with
terone acts synergistically with declining estrogen to reduce vaginoscopy. The vagina of the bitch is relatively long com-
edema of the vulva and vagina, which can be appreciated on pared with other domestic animals; the total length from the
vaginoscopic exam, and to cause the bitch to accept copula- cervix to the vulva (including the vestibule) has been reported
tion. Other observable clinical signs of ovarian luteiniza- to be 10 to 14 cm in an 11-kg bitch. The canine cervix is not
tion (production of progesterone) are minimal. Serial blood accessible by digital palpation per vaginam nor can it be
samples performed every 2 days once vaginal cytology is visualized with an ordinary vaginal speculum or otoscope;
roughly 70% superficial cells can be used to identify the both are too short. Consequently, equipment for visualizing
initial rise in progesterone (usually > 1.5 ng/mL), which the entire vagina and approaching the canine cervix or
indicates the LH surge has occurred. Progesterone can be accessing the uterus from the vagina must be long (e.g., up
assayed by radioimmunoassay (RIA) or chemiluminescence to 29 cm for large breeds, 33 cm for giant breeds) (Fig.
at most veterinary commercial laboratories. Several in-house 54.14). In addition, the presence of vaginal mucosal folds
semiquantitative kits are also available. Human laboratories and the position of the cervix in the bitch require the use of
are acceptable if previously cross-checked with a veterinary rigid equipment to access the cervix; pediatric proctoscopes
laboratory for comparability. By examination of the range suffice for visualization of the vaginal mucosa, but fiberoptic
and overlap of progesterone values at different points in pro- vaginoscopes permit superior optics and multiple channels
estrus and estrus, it becomes clear that no one absolute value for sampling and insemination (Figs. 54.15, 54.16, 54.17).
of progesterone correlates to any particular event. Progester- Hormone-induced changes in the vaginal mucosa enable
one varies at the point of the LH surge from 0.8 to 3.0 ng/ estrual bitches to tolerate vaginoscopy without sedation or
mL, from 1.0 to 8.0 ng/mL at ovulation, and from 4.0 to anesthesia.