Page 977 - Small Animal Internal Medicine, 6th Edition
P. 977

CHAPTER 54   The Practice of Theriogenology   949


              Estrus is the period of sexual receptivity and lasts an   Three alternatives following estrus are possible in the
            average of 7 days (3-16) and then subsides for an average   queen: (1) ovulation does not occur, and an average 9-day
  VetBooks.ir  of 9 days (3-14). The external genitalia have no conspicu-  (4-22) interestrus occurs before the next proestrus; (2) ovu-
                                                                 lation occurs without fertilization, resulting in a 35- to
            ous changes in appearance, but behavioral changes are pro-
            nounced during estrus. Because of the relatively short length
                                                                 (3) pregnancy. Pseudopregnancy occurs when ovulation and
            of  proestrus,  the  ability  to  inadvertently  induce  ovulation   40-day pseudopregnancy and a 1- to 10-day interestrus; or
            by mechanical vaginal stimulation, and the less dramatic   corpora  lutea  formation  occur  but  not  conception.  The
            cellular changes observed in the queen, vaginal cytology is   corpora lutea produce progesterone, with levels rising rapidly
            not used as commonly in the queen as it is in the bitch.   from basal concentrations to a peak of 16 to 17 ng/mL 18 to
            Behavioral observations should dictate the best time to place   25 days postovulation. After the peak, progesterone concen-
            the queen with the tom. Estrus duration is unaffected by   trations decline to basal at approximately 40 days postovula-
            breeding or ovulation. If vaginal cytology is desirable, flush-  tion. The normal pseudopregnancy duration lasts 35 to 40
            ing a small amount (<1.0 mL) of saline in and out of the   days. The corpora lutea appear to have a preprogrammed
            vagina provides better results than using a swab. Interestrus   finite life span in that they are not subject to regression from
            is the period between successive estrus periods if ovula-  uterine sources of prostaglandins. Lactation (pseudogenetra)
            tion does not occur. If the queen is not bred or otherwise   at the end of pseudopregnancy is less common in the queen.
            stimulated to ovulate, estrus will occur every 2 to 3 weeks   Induction of pseudopregnancy eliminates the so-called con-
            during the appropriate photoperiod. If the queen ovulates,   stant estrus seen in nonovulating queens; the duration of that
            corpora lutea are  formed  and  secrete  progesterone.  If  the   estrus is not changed. After pseudopregnancy, the queen will
            queen is not pregnant, diestrus (pseudopregnancy) results   go through a 2- to 4-week anestrus and either return to
            and lasts 35 to 40 days. Anestrus is the seasonal period   estrus if she is cycling or transition into a prolonged seasonal
            when  the  cat  does  not  cycle;  artificial  lighting  can  alter    anestrus.
            its occurrence.                                        Gestation in the cat is 63 to 66 days when measured from
              Queens are induced ovulators and ovulate in response to   a fertile mating. Because kittens born before 60 days of gesta-
            vaginal stimulation; however spontaneous ovulation can   tion have little chance of survival, it is important that gesta-
            occur in the queen. Ovulation is most commonly triggered   tion progress to 63 days for maximum kitten viability.
            by copulation or mechanical stimulation of the vagina, which   Because queens are induced ovulators, clients should be
            causes a reflex stimulation of the hypothalamus via pathways   counseled to recognize the signs of estrus and place queens
            in the spinal cord. The hypothalamus releases GnRH, which   with tomcats for the minimal time to accomplish a fertile
            then causes a release of LH from the anterior pituitary. LH   mating (usually 2-3 days), making evaluation of the length
            then stimulates ovulation and the development of corpora   of gestation more predictable. Unlike in the pseudopregnant
            lutea. Other forms of stimulation can occasionally be respon-  queen, corpora lutea do not regress in the pregnant queen;
            sible for ovulation; active corpora lutea have been found in   despite placental progesterone production, the ovaries are
            cats unexposed to males or artificial coital stimuli. Ovulation   needed to maintain pregnancy past day 50. As in the bitch,
            depends on adequate LH release, with both a peak concen-  progesterone concentrations vary over time. Prolactin from
            tration and duration of elevation being important. The LH   the anterior pituitary also appears to be required for preg-
            release occurs within minutes of coitus and peaks about 1 to   nancy maintenance.
            2 hours later. Release of LH is partially dependent upon the
            duration of prior exposure to estrogen (time in estrus), so
            the LH response varies depending on the day of estrus at   OBSTETRICS
            which coitus occurs. Multiple copulations result in higher
            concentrations of plasma LH and are more likely to result in   PREGNANCY DIAGNOSIS
            ovulation than a single mating. The duration of elevated LH   Early pregnancy evaluation permits optimal obstetrics (Table
            in plasma also determines whether ovulation occurs, with   54.2). Pregnancy detection by abdominal palpation (best at
            LH decreasing to baseline values within 12 to 24 hours after
            a single mating or after multiple matings at less than 2-hour
            intervals. However, LH remains elevated up to 38 hours after    TABLE 54.2
            multiple mating intervals every 3 hours. To achieve sufficient
            LH release, repeated breeding at a reasonable interval should   Methods for Pregnancy Diagnosis
            be encouraged. The LH response to a single mating can vary   GESTATIONAL AGE
            substantially, and neither single nor multiple copulations can   (FROM LH SURGE)  METHOD
            ensure ovulation. To increase the likelihood of ovulation,
            breeders should try to maximize the number of matings and   25+ days     Abdominal ultrasound, abdominal
            breed on successive days of estrus. Ovulation occurs 24 to                palpation
            60 hours postcoitus and may vary depending on the mating   >20-31 days   Witness Relaxin (Pfizer/Zoetis)
            pattern. Ideally, if the onset of estrus has been detected,   >50 days   Radiography
            breeding should occur on days 2 to 3.
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