Page 981 - Small Animal Internal Medicine, 6th Edition
P. 981

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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