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"For grantees that have no background in regulatory processes, it’s a relief to know that Found Animals will provide the support necessary to guide a successful product over those hurdles." Michael Munks, PhD, National Jewish Health, Michelson Grant Recipient

Canine and Feline Reproduction Resources

GETTING STARTED WITH A MICHELSON GRANT IN REPRODUCTIVE BIOLOGY GRANT PROPOSAL
Shirley D. Johnston, DVM, PhD, DACT, Director of Scientific Research
s.johnston@foundanimals.org


Foundation staff and members of the Scientific Advisory Board of the Michelson Prize & Grants program actively seek Letters of Intent and Full Proposals for grant funding in search of a single-dose, nonsurgical, safe, permanent, and effective sterilant in male and female dogs and cats that would be suitable for administration in a field setting, have a viable pathway to regulatory approval, and have a reasonable manufacturing process and cost. The Foundation’s mission is to reduce shelter euthanasia of pets. The Foundation funds basic, proof-of-concept and clinical reproductive research, and research using laboratory animals as models for dogs and cats. The latter will be considered only if the grant applicants justify the work as a preliminary step toward development of a dog and cat sterilant. The Foundation funds research into products that might be effective in only a single species (canine or feline) or gender (male or female), but the Michelson Prize will be awarded only for a sterilant that is effective in both male and female cats and dogs.

The Foundation envisions that the successful product will be a veterinary prescription item, with an approval pathway through the Center for Veterinary Medicine of the U.S. Food and Drug Administration. The successful product will most likely be injectable, not orally administered, in order to facilitate safe and effective administration to individuals in shelter settings. The Foundation has been advised that a bait product for this purpose would not likely achieve regulatory approval. Scientists interested in applying for grant funding from the Foundation should familiarize themselves with reproductive anatomy and physiology of the dog and cat in order to optimize their chances for success. Some “Fast Facts” and a selected reference list are listed below; these are intended for quick information only, and are not a substitute for a thorough literature review on reproductive anatomy, physiology, and previous research on nonsurgical sterilization methods in these species.

 

Fast Facts on Canine and Feline Reproduction and Sterilization

The Female Dog [Bitch] – Reproductive Anatomy & Physiology
The Male Dog [Dog] – Reproductive Anatomy & Physiology
The Female Cat [Queen] – Reproductive Anatomy & Physiology
The Male Cat [Tom] – Reproductive Anatomy & Physiology

The Female Dog [Bitch] – Reproductive Anatomy & Physiology

  • Sexual Differentiation and Normal Anatomy
    • The chromosomal complement of the bitch is 78,XX, or 39 pairs, including two X chromosomes.
    • The canine ovaries are paired oval organs, located in the abdominal cavity caudal to the kidneys. Size varies with size of the dog.
    • At birth, the ovary of the female Beagle puppy measures 4x3x2 mm, and contains, histologically, medullary and cortical regions. The cortex contains oogonia and pregranulosa cells.
    • Cross sectional area of the largest mid-sagittal section of the ovary of the adult Beagle bitch averages 66 mm2.
    • The uterine tube (oviduct), located predominantly on the surface of the ovary, is the site of fertilization; the uterine tubes transport oocytes to the uterus. A functional closure at the uterotubal junction prevents retrograde flow of uterine fluid into the uterine tubes.
    • The canine uterus is a Y-shaped organ consisting of a neck or cervix, a short body, and long uterine horns.
    • The canine cervix is an abdominal organ, composed of smooth muscle that contains the cervical canal; the cervix averages 1.5 to 2 cm in length. The cervical canal is not patient to passage of fluid except prior to puberty, during proestrus and estrus, and at parturition and postpartum. The abdominal location of the cervix, length of the vagina, and different sizes of dogs limits ease of cannulation of this organ.
    • The vagina extends from the cervix to the vestibule, and averages 10-14 cm in length in the Beagle bitch.
    • The vestibule extends from the vulva to the beginning of the vagina, near the external urethral orifice. During proestrus and estrus the wall of the vestibule becomes dilated, congested and edematous.
 
  • Puberty
    • The puberal estrus in dogs generally occurs between 6 and 24 months of age, with smaller breeds exhibiting earlier puberal estrus than large breeds.
    • The puberal estrus in dogs is not known to be influenced by season of the year or by photoperiod.
 
  • The Canine Estrous Cycle
    • The estrous cycle of the bitch is nonseasonal and monestrus, with only one estrus per estrous cycle.
    • Average interestrous interval is seven months, with a range of 4 to 12 months; this interval is not influenced by photoperiod or by whether pregnancy has occurred.
    • The wolf, coyote, Australian dingo and African basenji dog may have only one, seasonal, estrus each year.
    • Proestrus is the stage of the estrous cycle characterized by onset of vulvar swelling, serosanguinous vulvar discharge, and attraction of males in the absence of receptivity of the bitch to mating; proestrus is associated with rising serum estradiol of ovarian follicular origin and with a duration of 9 (range 0 to 27) days.
    • Estrus is the stage of the estrous cycle characterized by receptivity to mating. Estrous behavior in the bitch includes standing still, with the tail deflected up or to the side of the perineum (“flagging”) when the male sniffs the vulva and attempts to mount. Estrus duration averages 9 days (range 4 t to 4 days), with spontaneous ovulation usually occurring about 3 days after onset of estrus. Preovulatory luteinization permits detection of an elevation in serum progesterone prior to, and as a predictor of, ovulation. The bitch ovulates primary oocytes.
    • Diestrus is the third stage of the canine estrous cycle. Diestrus begins with a change in the morphology of exfoliated vaginal epithelial cells from cornified to noncornified, which occurs approximately 5-7 days after ovulation, and usually about 3 days prior to the end of behavioral estrus. Diestrus is characterized by serum progesterone concentrations (of ovarian, luteal origin) greater than 2 ng/ml, reaching peak concentrations 20-30 days into this stage, with subsequent gradual decline to less than 1 ng/ml at the end of the stage. Duration of canine diestrus is approximately 60 days; it ends with parturition in the pregnant bitch or with decline in serum progesterone to less than 1 ng/ml in the nonpregnant bitch.
    • Anestrus is the quiescent stage of the canine reproductive cycle, during which time the ovaries are relatively inactive. Average duration of anestrus in the bitch is 4 (range 2-10) months.
 
  • Mating Behavior and Purpose Breeding
    • Best conception rate and litter size are achieved in dogs when insemination occurs about 2 days after ovulation.
    • Ovulation is not temporally related to onset of proestrus or estrus; therefore, best breeding management to optimize conception and litter size includes (1) breeding every other day during behavioral estrus, or (2) using the preovulatory increase in serum progesterone or luteinizing hormone concentration to predict ovulation day.
    • Bitches and dogs should be housed apart until the bitch exhibits proestrual behavior.
    • After a few days of proestrus, the male and female should be introduced on leads, and the female observed for receptive behavior, which includes flagging, presenting the vulva to the male, and standing still in his presence instead of turning to snarl at him or sitting down.
    • If the bitch exhibits estrous behavior in the presence of the male, both animals should be permitted to play off-lead, and to mate naturally.
    • The male dog mounts the female and achieves intromission with the non-erect penis, due to penile rigidity conferred by the presence of an os penis in the male of this species. The penis engorges inside the vagina, preventing its withdrawal (the “tie” or “copulatory lock”) and the first two fractions of semen are ejaculated during rapid pelvic thrusting by the male (1-2 minutes). The male will then dismount with the erect penis still inside the vagina, and turn and stand end to end with the bitch for a few minutes up to 30-40 minutes, during which time prostatic fluid is ejaculated.
    • After ejaculation the erection subsides, and the penis can be withdrawn from the vagina; attempts to forcibly separate the bitch and dog during the copulatory lock are traumatic to both.
 
  • Pregnancy and Parturition
    • Ovulated oocytes are fertilized in the uterine tubes, and enter the uterine horns as zygotes 7-11 days after ovulation.
    • Implantation occurs 14-16 days after ovulation.
    • The dog has endothelialchorial placentation, so the endothelium of the uterine vessels lies adjacent to the fetal chorion. Placentation is zonary in this species.
    • Pregnancy diagnosis usually is performed about 4 weeks after ovulation, using abdominal palpation of fetal vesicles, abdominal ultrasonography of fetal vesicles, or serum relaxin concentrations. Maintenance of pregnancy in the bitch depends on the secretion of ovarian (luteal) progesterone.
    • Duration of pregnancy in the bitch averages 62-64 days, timed from ovulation; and 58-72 days timed from a single breeding.
    • Predictors of day of parturition in the bitch include breeding and ovulation dates, drop in rectal temperature which occurs 8-24 hours prior to parturition, and decline in serum progesterone at the end of pregnancy.
    • Stage I of parturition (6-12 hours) is time of synchronous uterine contractions leading to complete cervical dilation.
    • Stage II of parturition (6-24 hours) is time of expulsion of the puppies through the birth canal.
    • State III of parturition is time of expulsion of placentas/fetal membranes, which occurs during stage II labor or slightly thereafter.
 
  • Prevention of Fertility
    • Ovariohysterectomy causes permanent estrus suppression in the bitch, and can be performed safely in puppies as young as 6 weeks of age. It is performed using aseptic technique with the bitch under general anesthesia. The procedure causes permanent estrus suppression, prevents subsequent ovarian and uterine disease, and, if performed in bitches younger than 2 years of age, confers protection against later mammary neoplasia.
    • Uterine horn occlusion by electrocautery or ligation has been performed via laparotomy or laparoscopy in the anesthetized bitch, leading to prevention of pregnancy, but does not prevent estrual cycling, and may lead to fluid filling of the uterine segments cranial to the occlusion site.
    • Progestogens (megestrol acetate, medroxyprogesterone acetate) administered orally or parenterally are effective in suppressing estrus, but chronic use induces undesirable side effects such as cystic endometrial hyperplasia and pyometra; mammary hypertrophy; mammary neoplasia; and diabetes mellitus.
    • Androgens (mibolerone) administered daily will suppress estrus, clitoral hypertrophy and epiphora are undesirable side effects.
    • Vaccination against Gonadotropin Releasing Hormone (GnRH) has been demonstrated to cause temporary, but not permanent, cessation of reproductive function in the dog.
    • Deslorelin, a GnRH agonist, has been shown to temporarily suppress ovarian activity in the bitch, but duration of effect is variable.
    • Vaccination against canine zona pellucida (ZP) proteins but not vaccination against porcine ZP vaccines, may cause temporary and variable cessation of reproductive function in the bitch.
    • Pregnancy termination in the bitch has been reported with administration of prostaglandin F2α after day 40 of pregnancy or the antiprolactin drug, cabergoline, starting 30 days after mating.

The Male Dog [Dog] – Reproductive Anatomy & Physiology

  • Sexual Differentiation and Normal Anatomy
    • The chromosomal complement of the male dog is 78,XY.
    • The canine testes pass from the abdomen into the scrotum via the inguinal canal by about 5 days of age; the inguinal canal remains open until about 6 months of age, often permitting free movement of the testes proximal to the scrotum until closure of the canals is complete.
    • Spermatogenesis begins at about 20 weeks of age in the dog, and sperm first appear in the ejaculate at about 7 to 9 months of age, depending, in part, on size of the dog.
    • Resting serum testosterone concentrations in intact adult male dogs ranges from <0.5 to more than 5 ng/ml. Testosterone is secreted in pulsatile bursts in male dogs, so measurement of serum testosterone in a single, random blood sample usually is not diagnostic of abnormal concentrations.
    • The prostate is the only accessory sex gland of the male dog; it is a retroperitoneal pelvic or abdominal organ that encircles the urethra at the neck of the urinary bladder. The prostate secretes the third and major fraction of the ejaculate volume. The canine prostate is an androgen dependent organ that increases in size with age in the intact male and atrophies following castration.
    • The canine penis is directed cranially and is composed of the root, the body, and the glans penis. An os penis runs through the penis, dorsal to the penile urethra.
    • During mating, the presence of the os penis permits intromission prior to onset of complete erection; following ejaculation of the sperm rich fraction of the ejaculate, the male dog dismounts from the bitch and turns to stand tail to tail with her in the copulatory lock, so that the penis is twisted 180 degrees in a lateral plane.
 
  • Puberty
    • Spermatogenesis begins at about 20 weeks of age, and spermatozoa are present in the epididymis after 32 weeks of age.
    • Age at which first ejaculation of sperm occurs in the dog varies by breed (average 5 to 10 months); in general, smaller-breed dogs achieve physical maturity and puberty earlier than large breed dogs.
    • Most male dogs will ejaculate semen containing sperm by the time they are 12 months of age; however, some early ejaculates may be azoospermic, and some large breed dogs many not ejaculate until as late as 18 months of age.
    • Serum testosterone concentrations increase after 24 months of age, reaching adult concentrations by approximately 32 weeks of age.
 
  • Semen Collection and Evaluation
    • Semen can be collected by manual stimulation of the penis using a latex artificial vagina and plastic collection tube in most intact male dogs; collection is enhanced by the presence of an estrous teaser bitch.
    • Electroejaculation has been reported in the dog, but is not recommended, as it requires general anesthesia, an appropriate probe and ejaculation device, and has been associated with urine contamination of the ejaculate.
    • Canine semen is ejaculated in three fractions: the presperm fraction (volume 0.5 to 5.0 ml), the sperm rich fraction (volume 1.0 to 4.0 ml) and the prostatic fluid fraction (1.0 to >80.0 ml).
    • Total volume of the canine ejaculate ranges from 2.5 to > 80.0 ml; color of the normal ejaculate is opalescent white.
    • Concentration of sperm in a normal canine ejaculate varies greatly, depending on how much of the third (prostatic fluid) fraction is collected.
    • Total sperm per ejaculate varies by size of the dog, and ranges from 300 to 2,000 x 106.
    • A normal dog ejaculate contains more than 70% progressively motile sperm, and more than 80% morphologically normal sperm, with pH ranging from 6.3 to 6.7.
    • Dog semen is not sterile, because it contacts the urethral mucosa that has a resident population of bacteria.
    • Normal dog seminal plasma contains > 5,000 U/l of alkaline phosphatase, which is secreted by epithelial cells of the epididymides.
 
  • Prevention of Fertility
    • Castration (bilateral orchiectomy) is the most common form of sterilization of male dogs, and is the treatment of choice at this time. It is performed using aseptic technique with the male under general anesthesia. It is easy, effective, irreversible, and eliminates most objectionable reproductive behaviors. Sperm may be present in the ejaculate for as long as 21 days after castration.
    • Vasectomy and injection of epididymal sclerosing agents have been used to sterilize male dogs, but are not considered superior to castration.
    • Chemical castration has been used to cause sterility in male dogs using intratesticular injection of zinc-containing and other compounds.
    • Progestational drugs have been used to suppress the pituitary-adrenal axis, with some products suppressing spermatogenesis. In the dog, however, chronic use of progestogens is associated with undesirable side effects such as diabetes mellitus and mammary nodules.
    • GnRH agonists have been demonstrated to cause decline in serum luteinizing hormone and testosterone concentrations in the male dog, with nondetectable concentrations occurring by 14 days, and duration of sterility for 6 to 12 months following a single administration.
    • Vaccination against GnRH has been demonstrated to cause variable, temporary cessation of reproductive function (testosterone secretion and spermatogenesis) in the dog.

The Female Cat [Queen] – Reproductive Anatomy & Physiology

  • Sexual Differentiation and Normal Anatomy
    • The diploid number of chromosomes in somatic cells of the female cat is 38, or 19 pairs including two X chromosomes (38XX).
    • Ovarian morphology, with primitive medullary and cortical regions, is fully established in the kitten fetus by 40 days or 75 mm crown-rump length.
    • Ovaries of most newborn kittens contain primordial ova surrounded by granulosa cells.
    • Ovaries of the adult queen are approximately 1.0 x 0.3 x 0.5 cm in size, and 220 mg in weight.
    • The uterine tube (oviduct) of the adult queen is 5-6 cm in length; the uterus is a Y-shaped organ consisting of a 2 cm long body and two 10 cm uterine horns; size of the uterus depends on the size, age, and parity of the cat, and on phase of the estrous cycle or pregnancy.
    • The cervix is an abdominal organ in the cat, located about 40 mm cranial to the vulva; it is open during estrus and parturition, and closed during other stages of the estrous cycle.
    • The cervix is difficult to cannulate, even during estrus in the anesthetized cat.
    • The vagina of the adult queen is about 2 cm long, as is the vestibule, which extends from the vulva to the external urethral orifice.
    • The feline vestibular diameter can accommodate a 4 mm diameter probe introduced through the vulva; the feline vagina can accommodate a 1 mm diameter probe to the level of the cervix.
  • Puberty
    • The puberal estrus occurs in most queens between 4 and 12 months of age.
    • Onset of puberty is positively influenced by increasing size of the queen and by increasing day length in the photoperiod to which the queen is exposed.
    • Occasionally pregnant queens are observed that are only 4 months of age.
 
  • The Feline Estrous Cycle
    • The queen is seasonally polyestrous, with estrus induced by increasing day length.
    • The queen is an induced ovulator, that ovulates in response to coitus or vestibular stimulation; however, some queens (up to a third) housed individually have been demonstrated to ovulate without coital contact, perhaps in response to visual or pheromone cues in the absence of vestibular stimulation.
    • In the absence of ovulation, and in the presence of 14 hours bright light per day, feline estrous cycles occur at 4 to 30 (14-19 modal) day intervals.
    • Prolonged anestrus results from decreasing or short day length.
    • Proestrus is a short (~1 day) stage of the estrous cycle that begins with rubbing of the head and neck against adjacent objects in queens that do not accept mating; proestrus occurs in only about 20% of normal, intact queens.
    • Estrus is the behavioral stage of accepting mating by the male; in the cat, this stage occurs during peak follicular estradiol secretion (serum concentrations of 30-70 pg/ml estradiol). Estrous behavior includes crouching with the forequarters pressed to the ground and hyperextension of the back (lordosis) with presentation of the vulva for mating. Estrous queens vocalize and show restlessness and head rubbing, treading with the hind legs, and tail deviation. Duration of feline estrus ranges from 2 to 19 days, and is reported to last about 6 days in the absence of coital contact, and 8-9 days in the presence of coital contact, whether or not ovulation is induced. Following estrus, the queen may enter diestrus, if induced to ovulate, postestrus followed by another estrus cycle under adequate photoperiod, or seasonal anestrus.
    • Luteinizing hormone (LH) release from the pituitary gland is induced by copulation; magnitude of LH release increases with increased number of copulations. A single copulation induces ovulation in only about half of the queens bred.
    • Postestrus is an 8-10 day period of reproductive quiescence that follows one estrus and precedes the next one in queens that have not been induced to ovulate. Postestrus is followed by proestrus/estrus.
    • Diestrus is the period that follows (fertile or nonfertile) ovulation in the queen; during this time the corpora lutea of the ovaries secrete progesterone reflected in a bell-shaped curve of serum concentrations over time, peaking at about 30-40 ng/ml approximately one month after ovulation. Diestrus lasts about 40 days in the non-pregnant queen (also called pseudopregnant) and about 60 days in the pregnant queen. Diestrus ends when serum progesterone concentrations fall below 1.5 ng/ml.
    • Anestrus is seasonal absence of cycling activity that occurs in the late autumn months (October, November, December) in queens exposed to natural photoperiods in the Northern Hemisphere. Serum estradiol and progesterone concentrations are at baseline levels during this stage. Anestrus is followed by proestrus/estrus associated with increasing day length.

  • Mating Behavior and Purpose Breeding
    • Queens and toms should be housed apart until the queen exhibits estrous behavior.
    • When an estrous queen is introduced to an intact male cat, she will prowl and exhibit estrous behavior prior to copulation.
    • Copulation includes 5 to 50 seconds of mounting and grasping of the back of the queen’s neck by the male’s bite, up to 8 minutes of positioning as the female raises and presents her vulva to the male, and up to 30 seconds for intromission, ejaculation, and a coital cry by the queen. The male then will dismount, and the queen will exhibit up to 7 minutes of an “after reaction,” consisting of vigorous, disoriented rolling, stretching, striking at the male, and genital licking/grooming. Copulations may exceed 30 in number over 36 hours.
    • Multiple copulations should be permitted in purpose breeding so as to ensure secretion of maximum concentrations of luteinizing hormone and resulting ovulations.
 
  • Pregnancy and Parturition
    • Ovulation follows coitus by 24 to 36 hours in the cat.
    • Ova are fertilized in the uterine tube, and pass into the uterine horn as morulae by day 4 to 5 post coitus.
    • Transuterine migration of embryos results in fetal number in the right and left horns to become evenly distributed.
    • Litter size ranges from 1 to 13 kittens, with average litter size of 4 to 5.
    • Implantation occurs 12 to 13 days after ovulation.
    • Placentation in the domestic cat is endotheliochorial (maternal and fetal circulations are separated by four tissue layers) and is zonary in shape.
    • Pregnancy diagnosis usually is accomplished by abdominal palpation of fetal vesicles or by abdominal ultrasonography about 4 weeks post- coitus.
    • Pregnancy duration averages 65 days from coitus, with a reported range of 52 to 74 days.
    • At parturition, the queen exhibits pacing and nesting behavior; when contractions begin she may assume a semi-squatting position; when contractions subside she may lay on her side and purr. Fluid usually is expelled from the vulva prior to delivery of the first kitten.
    • Once fetal tissue appears at the vulva, complete expulsion usually occurs in less than 5 minutes.
    • Posterior presentation is common, and does not predispose to dystocia in this species.
    • Most queens deliver kittens with ease over a period of several hours; average length of complete parturition is reported at 16 hours, with a range of 4 to 42 hours.
 
  • Prevention of Fertility
    • Ovariohysterectomy causes permanent estrus suppression in the queen, and can be performed safely in queens as young as 6 weeks of age. It is performed using aseptic technique with the queen under general anesthesia. The procedure causes permanent estrus suppression, prevents subsequent ovarian and uterine disease, and, if performed in queens younger than 2 years of age, confers protection against later mammary neoplasia.
    • Uterine horn occlusion by electrocautery or ligation has been performed via laparotomy or laparoscopy in the anesthetized queen, leading to prevention of pregnancy, but does not prevent estrual cycling, and may lead to fluid filling of the uterine segments cranial to the occlusion site.
    • Progestogens (megestrol acetate, medroxyprogesterone acetate) administered orally or parenterally are effective in suppressing estrus, but chronic use induces undesirable side effects such as cystic endometrial hyperplasia and pyometra; mammary hypertrophy; mammary neoplasia; and diabetes mellitus.
    • Androgens (mibolerone) administered daily will suppress estrus, but are associated with undesirable side effects of clitoral hypertrophy and urine spraying with tomcat-scented urine.
    • Vaccination against GnRH has been demonstrated to cause temporary, but not permanent, cessation of reproductive function in the cat.
    • Deslorelin, a GnRH agonist, has been shown to temporarily suppress ovarian activity in female cats, but duration of effect was variable.
    • Vaccination against feline zona pellucida proteins has been shown to cause temporary cessation of reproductive function in the cat; vaccination against heterologous ZP antigens is less effective.
    • Pregnancy termination in the queen has been reported with administration of prostaglandin F2α after day 40 of pregnancy or the antiprolactin drug, cabergoline, starting 30 days after mating.

The Male Cat [Tom] – Reproductive Anatomy & Physiology

  • Sexual Differentiation and Normal Anatomy
    • The chromosomal complement of the tom cat is 38,XY.
    • Testes of normal kittens usually are descended at birth, but prior to puberty (7-10 months of age in the male) cat testes move freely up and down in the inguinal canal.
    • Combined weight of the testes of male kittens is reported as 20-58 mg at birth, as 130 mg at 12 weeks of age, and as 500 mg at 20 weeks of age.
    • Earliest histologic evidence of spermatogenesis occurs at approximately 20 weeks of age, and earliest ejaculation of sperm occurs at about 7 months of age.
    • Resting serum testosterone concentrations in intact adult male cats range from <0.5 to more than 20 ng/ml.
    • The prostate of the adult male cat is an androgen-dependent organ approximately 1 cm in length that covers the urethra dorsally and laterally 2-3 cm caudal to the neck of the urinary bladder. The prostate atrophies following castration.
    • The bulbourethral glands are two 5 mm diameter pea-shaped glands located dorsolateral to the bulb of the penis. Both the prostate and bulbourethral glands contribute fluid to the ejaculate.
    • The glans penis of the adult, intact male cat is a 5-10 mm long conical structure directed caudally that contains a band of 120 to 150 androgen-dependent penile spines in 6 to 8 circular rows. The penile spines erupt between 9 and 13 weeks of age in intact male kittens. Penile spines atrophy after castration.
    • During its early formation, the penis adheres to the prepuce via the balanopreputial fold; dissolution of this fold is an androgen-dependent event that occurs at about 7-12 months of age, unless the cat is castrated prior to that time, in which case the adhesion persists.
 
  • Puberty
    • Earliest ejaculation of spermatozoa by the tom occurs at about 7 months of age, but the average age at which mating begins varies with physical condition, body size, and season.
    • Average onset of reproductive behavior and mating occurs at 8-10 months of age or at a body weight of 2.5 kg or more, whichever occurs first.
    • Male cats housed under controlled illumination of 12 hours of light per day do not exhibit seasonality of breeding behavior, but, rather, produce sperm and exhibit copulation all year.
 
  • Semen Collection and Evaluation
    • Feline semen has been collected using (1) conscious ejaculation of the trained tom into an artificial vagina, (2) electroejaculation of the anesthetized male, (3) vaginal lavage of the postcoital queen, and (4) cystocentesis from the tom following ejaculation. Of these methods, electroejaculation provides the cleanest, most reliable and complete ejaculate, but also is associated with greatest cost (of the electroejaculation device that administers voltage pulses via a rectal probe) and greatest stress to the anesthetized male cats. Not all research cats can be trained to consciously ejaculate into an artificial vagina.
    • Electroejaculation sometimes results in a clear (azoospermic) sample, even in normal male cats that will ejaculate sperm at the next attempt; semen with sperm is cloudy white in the cat.
    • Normal volume of semen in the adult male cat ranges from 0.01 to 0.8 ml.
    • Normal sperm numbers in the ejaculate of the adult male cat range from 10 to 70 x 106 per ejaculate.
    • Normal semen quality in the ejaculate of the adult male cat includes 60-90% progressively motile sperm, with approximately 70% morphologically normal sperm.
 
  • Prevention of Fertility
    • Castration (bilateral orchiectomy) is the most widely used method of preventing reproduction in the male cat, because it is easy, effective, irreversible, and eliminates most objectionable reproductive behaviors, much aggression, and urine marking with tomcat-odor scented urine. It is performed using aseptic technique with the male under general anesthesia. Sperm may be present in the feline ejaculate for as long as 49 days after castration.
    • Vasectomy and injection of epididymal sclerosing agents have been used to sterilize male cats, but are not considered superior to castration.
    • Progestational drugs have been used to alter male sexual behavior and semen quality in this species, but have undesirable side effects similar to those in queens.
    • Vaccination against GnRH has been demonstrated to cause variable, temporary cessation of reproductive function (testosterone secretion and spermatogenesis) in the cat.
Selected References:
  • Anderson AC, Simpson ME: The Ovary and Reproductive Cycle of the Dog (Beagle). Geron-X, Inc., Los Altos, CA, 1973.
  • Concannon PW, Castracane BD, Temple M, Montanez A: Endocrine control of ovarian function in dogs and other carnivores. Anim. Reprod. 6:172-193, 2009.
  • Johnston SD, Root Kustritz MV, Olson PNS: Canine and Feline Theriogenology. WB Saunders, Philadelphia, 2001.
  • Rhodes L, Moldave K: Contraception and Fertility Control in Animals, 2002.
  • Root MV, Johnston SD, Olson PN: Estrous length, pregnancy rate, gestation and parturition lengths, litter size, and juvenile mortality in the domestic cat. J Amer Anim Hosp Assoc 31:429-433, 1995.
  • Root Kustritz MV: The Dog Breeder’s Guide to Successful Breeding and Health Management. Saunders Elsevier, Philadelphia, 2006.

The Alliance for Contraception in Cats & Dogs (ACC&D) has recently released a new e-book entitled Contraception and Fertility Control in Dogs & Cats. This reference guide provides an extensive overview of the growing and dynamic field of non-surgical methods and research to manage reproduction in cats and dogs.