Page 986 - Small Animal Internal Medicine, 6th Edition

958 PART VIII Reproductive System Disorders

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A B

FIG 55.5
Vaginal hyperplasia. (A) Labrador Retriever bitch. Note mucosal hyperemia and abrasion
secondary to prolapse of vaginal tissue. (B) Recurrence at parturition causing obstruction
of the distal birth canal.

planned. It is doubtful that medical intervention is of benefit the United States. Depot forms of leuprolide acetate (Lupron
insofar as most bitches resolve this condition post ovula- [Tap Pharmaceutical]) are available on the human market
tion when estrogen levels normally decline. Successful sur- but remain extremely expensive. Although these products
gical methods of amputating the hyperplastic tissues have are effective and safer than previous options, their lack of
been reported. Prolonged (>1 month) vaginal hyperplasia/ availability and high cost make them impractical.
prolapse most commonly occurs with ovarian pathology
(follicular ovarian cysts), requiring ovariectomy for reso- ESTRUS INDUCTION
lution. Artificial insemination may be required because of Many protocols exist in the veterinary literature for estrus
vaginal hyperplasia, which can recur at term secondary to induction in the bitch and queen. Most have disappointing
increased estrogen levels associated with parturition (Fig. clinical results or use agents that are no longer commercially
55.5, B). The heritability of this condition is not known. available or are too cumbersome for clinical application.
Estrus (behavior and attractiveness) induction is straightfor-
MANIPULATION OF THE ward with estrogenic compounds, but estrus followed by
ESTROUS CYCLE ovulation of fertilizable oocytes that implant successfully is
difficult in the bitch and queen.
PREVENTION OF ESTROUS CYCLES Fertile estrus can be induced most reliably in the bitch
The best method to prevent estrous cycles in bitches and using dopamine agonists. At least 90 days of anestrus (pro-
queens not intended for future breeding remains ovariec- gesterone < 1.0 ng/mL) must be allowed for adequate uterine
tomy or ovariohysterectomy. Contraceptive vaccines gener- involution permitting implantation. Oral (PO) bromocryp-
ating antibodies to GnRH are under development and can tine at 30-50 µg/kg per day in divided doses can induce a
be used in both male and female dogs and cats, but these fertile proestrus in 17 to 49 days, but side effects (nausea and
are not yet commercially available. Temporary contraceptive diarrhea) are common and usually unacceptable. Cabergo-
measures for bitches and queens intended for future breeding line at 5 µg/kg PO q24h can induce fertile proestrus in 4 to 34
are problematic; progestins and anabolic compounds have days, with fewer side effects. The drug must be discontinued
undesirable side effects and risks (e.g., endometrial hyperplasia/ after 48 to 96 hours of proestrus (determined cytologically) to
pyometra, diabetes mellitus, mammary hyperplasia; hepa- prevent downregulation of the hypothalamic-pituitary-ovar-
topathy, behavioral changes, endometrial atrophy) and are ian axis. Fertile estrus induction has also been documented
not advised. GnRH agonists (leuprolide, lutrelin, deslorelin) with GnRH analogs (lutrelin, deslorelin, leuprolide) that can
have been shown to suppress gonadal activity in both male also be administered as long-acting dosage forms via subcu-
and female dogs, with few side effects. These agonists act by taneous (SC) injections, mini pumps, inhalants, or implants.
causing a downregulation of the GnRH receptors, often after Both expense and side effects may limit use of these prod-
an initial proestrus/estrus induction. Chronic suppression ucts. A synthetic sustained-release GnRH analog (deslorelin)
of LH and FSH concentrations and suppression of gonadal was marketed for several years for equine patients and shown
hormone secretion and gametogenesis eventually occurs (Trigg to be effective in canine patients, but it is currently not uni-
et al., 2006). The final result is a chemical castration of males versally commercially available. Substitutions (Ovuplant
and a protracted anestrus in females that is reversible. None [Fort Dodge]) are not U.S. Food and Drug Administration
of these products are universally available commercially in (FDA) approved and can have unreliable results. Side effects