Page 981 - Small Animal Internal Medicine, 6th Edition

CHAPTER 55
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Clinical Conditions of the

Bitch and Queen

NORMAL VARIATIONS OF THE ovulation timing and breeding (see Chapter 54). Intact male
ESTROUS CYCLE dogs typically note pheromones produced days to weeks
before the onset of proestrus and spend more time sniffing
LATER THAN TYPICAL PUBERTY the bitch or her urine. Performing monthly progesterone
The onset of the first estrous cycle occurs after a bitch attains assays permits retrospective identification of estrus but will
70% of her adult height and body weight. Small breeds gen- not facilitate breeding in that cycle unless acquired before
erally begin their first estrous cycle between 6 and 10 months diestrus. Silent heat cycles must be differentiated from true
of age; large breeds can begin as late as 18 to 24 months, primary anestrus. True primary anestrus in the bitch that
which causes owner concerns. Family histories (dam and fails to experience an estrous cycle is most likely due to a
female siblings) can help predict the anticipated onset of disorder of sexual development and is uncommon.
reproductive cycling. Efforts at differentiating delayed
puberty (as perceived by an owner) from an actual failure to SPLIT HEAT CYCLES
have reproductive cycles should be postponed until a bitch Bitches with split heat cycles, in which proestrus and possi-
is at least 2 to 2.5 years old. Bitches with delayed puberty bly early estrus occur without ovulation or progression to
generally have normal reproductive cycles once initiated. diestrus, can be thought to have abnormally short cycles,
Housing such a bitch with another cycling bitch can promote lack of sexual receptivity, or infertility if breedings were
her proestrus secondary to the pheromone-related “dormi- forced or artificial insemination performed without con-
tory effect.” Estrous induction protocols (later in this chapter) firming ovulation. Waves of folliculogenesis with increased
can be attempted if the bitch is mature (i.e., at least 24-30 estrogen production but without ovulation occur in split
months of age) and breeding is desired. heats. Follicular atresia follows, no luteal phase with proges-
Puberty in the queen usually occurs at 9 to 10 months of terone production occurs, and normal sexual receptivity fails
age. Puberty can occur as early as 4 months or as late as 2 to develop. These cycles typically occur in young bitches and
years; because cats are seasonal breeders, the season in which are characterized by periods of hemorrhagic vulvar dis-
the kitten was born influences the age at which puberty charge typical of proestrus, attractiveness to males, and
occurs. Cyclicity is dependent on the photoperiod, with usually no receptivity. In young bitches, split cycles are
queens requiring 12 hours or more of light to maintain thought to be due to immaturity. These cycles can also occur
normal cycling. in mature bitches with a history of normal past cycles, usually
in association with stress. Increased endogenous cortisol
SILENT HEAT CYCLES levels associated with stress (travel, shipping, kenneling) may
The occurrence of a silent heat cycle must be ruled out inhibit the luteinizing hormone (LH) surge and associated
during evaluation of a bitch suspected of failing to have ovulation. Two to 10 weeks after a split cycle, another pro-
estrous cycles. Fastidious bitches with minimal vulvar swell- estrus typically begins and could proceed to ovulation. Even-
ing, scant vulvar discharge, and few behavioral changes can tually most young bitches with split heats progress through
have proestrus/estrus that escapes human detection (“silent”), a normal estrus to diestrus. The condition is not associated
especially in the absence of an intact male dog. Diestrus with reproductive pathology in the young or stressed bitch,
normally lacks clinical signs. Proestrus and estrus tend to and no treatment is recommended. Breeding a bitch in sur-
become more apparent as the bitch ages. Performing weekly roundings familiar to her is advised if stress might have
vaginal smears to detect cytologic proestrus, housing the altered a previous cycle. Delaying shipping of a bitch for
bitch near an intact male, or using white bedding can aid in breeding until after the LH surge (progesterone initial rise)
prospective detection of a silent heat, permitting proactive has occurred is optimal. Using shipped semen (chilled,

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