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Frequently asked questions about small-animal reproduction (Proceedings)
The estrous cycle of the bitch consists of proestrus, estrus, diestrus, and anestrus. Proestrus is the first stage of heat, when the bitch first shows swelling of the vulva and exudation of serosanguinous vulvar discharge. Male dogs are interested but she does not allow mounting. Estrus, or standing heat, is characterized by softening of the vulva, a change from serosanguinous to a more tan-colored discharge, and flagging and standing by the bitch.
"I want to get my dog bred and I need to know what to look for." – What are signs of heat in the bitch?
The estrous cycle of the bitch consists of proestrus, estrus, diestrus, and anestrus. Proestrus is the first stage of heat, when the bitch first shows swelling of the vulva and exudation of serosanguinous vulvar discharge. Male dogs are interested but she does not allow mounting. Estrus, or standing heat, is characterized by softening of the vulva, a change from serosanguinous to a more tan-colored discharge, and flagging and standing by the bitch. Flagging is lateral deviation of the tail and muscular elevation of the vulva when the perineal region is stimulated. When the bitch is standing to be bred, she allows the male to mount, and holds her rear limbs rigid. Diestrus and anestrus are the latter stages of the cycle, during which there are no characteristic physical changes.
The average bitch cycles about twice a year. She is in proestrus for about 7-10 days, and then in standing heat for about 7-10 days, for a total length of heat of about 3 weeks.
"When should I take my female dog to meet the male?" – How can we optimize breeding management in dogs?
The average bitch ovulates, or releases eggs from the ovaries, on about the second day of standing heat. Traditionally, people have bred dogs on days 9, 11, and 13 of heat (counting the first day of vulvar bleeding as day 1). Other people breed the bitch every other day while she's in standing heat. The latter method should cover the fertile window (from 3 days before to 4 days after ovulation). In bitches with a history of infertility or for whom multiple breedings cannot be performed, timing of ovulation is preferred. Optimal breeding day is 2 days after ovulation in bitches.
Ovulation timing cannot be done by assessment of vaginal cytology. While vaginal cytology can be used to help us determine where a bitch is in her cycle, with estrus defined as 100% cornification with greater than 50% anuclear squame cells and no PMNs present, there is no specific change in cytology that designates occurrence of ovulation.
Measurement of progesterone in serum is the preferred technique for timing of ovulation. Progesterone does not cause ovulation; luteinizing hormone (LH) from the pituitary stimulates ovulation in dogs and other species. A significant rise and fall in serum concentration of LH, which lasts at most 24 hours, occurs 2 days before ovulation. Because the spike in LH secretion is fairly short-lived, and because serum concentrations of LH before and after the peak cannot be distinguished from each other, assessment for the LH peak requires daily collection of blood samples from the estrous bitch, at about the same time each day. This is inconvenient and expensive. Finally, the only commercially available in-house LH assay has been on backorder for an extended period, and assays run at commercial laboratories have such a long turn-around time as to preclude their usefulness for breeding management in bitches.
Bitches undergo a process called preovulatory luteinization, in which the lining of the ovarian follicles containing the eggs begins to secrete progesterone prior to ovulation. Fortunately for us, this increased secretion of progesterone occurs in a fairly uniform manner, allowing us to use progesterone as an indicator of the LH peak and ovulation. Progesterone continues to rise after ovulation. Progesterone can be measured with semi-quantitative in-house tests, which are not as accurate but have short turn-around time, or commercial laboratory assays, which are very accurate but have longer turn-around times. Progesterone interpretation for breeding timing is done as follows:
3) "My dog is in heat and she's stuck to the dog next door. Should we hit them with the hose or try to pull them apart? What can we do to keep her from having pups?" – What actually is happening during the copulatory lock (tie) in dogs? What options exist for pregnancy termination in dogs?
Do not try to pull dogs apart during the copulatory lock! When dogs are tied, the engorged proximal portion of the penis is caught within the muscular lips of the vulva and pulling the dogs apart is painful to them. The male deposited all the spermatozoa during the initial thrusting before the tie occurred anyway, so the bitch is not less likely to become pregnant if you pull them apart. Finally, do not squirt them with a hose – then they'll just be stuck together and wet.
For pregnancy termination, an initial determination of likelihood of pregnancy having occurred is warranted. If no breeding was witnessed or if the bitch is not in a fertile part of her cycle, it is obviously inappropriate to treat with potentially harmful drugs if likelihood of pregnancy is small. The bitch should be evaluated within a day of the inappropriate breeding for assessment of stage of the cycle (vaginal cytology and measurement of serum progesterone concentration). Lack of spermatozoa on vaginal cytology does not preclude the possibility of breeding having been accomplished. Also remember that the spermatozoa of normal male dogs can live in the reproductive tract of normal female dogs for up to a week, so if the bitch is early in her season, she may still become pregnant from a single breeding days before.
Ovariohysterectomy (OHE) should always be offered as the first consideration. If the owner wants to maintain the bitch intact for future breeding, or if the bitch is in advanced pregnancy, medical options exist. The traditional "mismate shot" is estradiol cypionate. Estradiol terminates pregnancy by altering movement of the egg through the uterine tube and altering implantation within the uterus. To be effective and safe, it must be given after ovulation (serum progesterone > 4 ng/ml) but before the onset of diestrus (diestrous vaginal cytology is completely non-cornified). If the drug is given before ovulation, it will not be effective. If it is given in diestrus, it may induce pyometra. The other commonly available medical therapy is prostaglandin F2alpha (PGF2alpha). PGF2alpha (Lutalyse™) acts by lysing the corpora lutea and decreasing serum progesterone concentrations to a level incompatible with pregnancy, and by contracting the uterus to physically break down the pregnancy. It can be given safely at any stage of gestation after the fifth day of diestrus. Side-effects are transient, and include vomiting, diarrhea, and hypersalivation. There are no reports of altered fertility with the use of PGF2alpha but it is not approved for use in bitches as a pregnancy terminating agent in the United States. Two studies have reported that only about 2/3 of dogs presenting for pregnancy termination are pregnant, so this is the drug I prefer since it can be given safely and effectively after pregnancy has been confirmed and non-pregnant dogs are not treated unnecessarily. A final medical option for pregnancy termination is dexamethasone. This is administered orally for 10 days after mid-gestation. It is inexpensive and is reported to be effective 80% of the time. If it is not effective, pups born are reported to be normal.
"Is there an EPT for dogs?" – What techniques exist for pregnancy diagnosis in dogs and when are they accurate?
There is no early pregnancy test (EPT) for bitches. In humans, the conceptus and mother make a hormone that is very specific to normal pregnancy, human chorionic gonadotropin, which can be measured in the mother's blood or urine within 2 weeks of conception. No pregnancy specific hormone has been identified in dogs. Currently available pregnancy diagnostic techniques, the time when they are appropriately used, and their accuracy are described below.
"My male dog can't seem to figure it out. Can you help us get a female bred?" – How is artificial insemination performed in dogs?
Inexperienced male dogs may simply require someone to hold the bitch still so she doesn't move around so much as to startle or distract the male and may benefit from initial breeding to an experienced bitch. If no physical or psychological solution can be found to permit natural breeding to occur, artificial insemination (AI) can be performed. AI can be done using fresh, chilled, or frozen semen. Fresh semen is used exactly as it is collected. Chilled semen is centrifuged and the pellet resuspended in extender, a medium containing nutrients, buffers, and antibiotics. The semen is chilled to refrigerator temperature and shipped for insemination within 24-48 hours of collection. Frozen semen is prepared by centrifuging the semen, resuspending the pellet in extender and a cryoprotectant, and freezing it in liquid nitrogen in either pellets or straws. The semen is good indefinitely as long as it remains in liquid nitrogen; once thawed, it is only viable for a matter of hours.
Insemination can be vaginal, in which the semen is deposited in the mid-vagina with a pipette and the bitch's hindquarters elevated to allow pooling of the semen around the external cervical os, or intrauterine. Vaginal insemination is appropriate for fresh or chilled semen. Intrauterine insemination is required with use of frozen semen, which has a short lifespan and altered motility after thawing and is less likely to get through the cervix and to the uterine tube to fertilize eggs if deposited in the vagina. Intrauterine insemination can be performed via laparotomy or with use of a rigid endoscope and passage of a polypropylene urinary catheter through the cervix.
Any time AI is performed, ovulation timing with measurement of serum progesterone is strongly recommended to minimize the number of procedures performed. Ovulation timing is essential when using chilled or frozen semen.
"My dog is having puppies. How can I tell if everything is going okay?" – What is the normal sequence of parturition in dogs?
In dogs, the fetuses initiate parturition, so bitches carrying only one pup or carrying dead pups may not spontaneously enter labor. Serum progesterone concentrations fall abruptly in the last 1-2 days of gestation, causing a transient decline in body temperature to less than 99 degrees F, which may be appreciated by the owner if they are taking the dog's rectal temperature several times daily in the week before expected parturition.
Labor occurs in three stages. The first is cervical dilation; the bitch is restless and pants, nests, refuses food, and may vomit. No abdominal contractions are visible. This stage may last as long as 12 hours. The second stage is passage of puppies. Puppies may be born either head first with forelimbs extended (cranial presentation) or rear end first with tail and hindlimbs extended (caudal presentation), and may be within the amniotic sac when born. From the first obvious abdominal contractions, a pup should be born within 4 hours. No more than 2 hours should elapse between pups. Abnormalities of second stage labor include prolonged labor with no pups produced; obvious malpresentation of a pup (for example, single limb protruding from the vulva); and passage of abnormal vulvar discharge (frank hemorrhage, purulent fluid, +/- green fluid [indicates placental separation]). Third stage labor is passage of the placentas and usually occurs along with second stage labor, with the bitch passing a puppy and then the placenta 5-15 minutes later. If it does not disturb the bitch unduly, placentas should be removed and the bitch not allowed to eat them. They have no nutritional or hormonal value and may cause gastroenteritis.
If the owner is concerned that dystocia (abnormal delivery) may be occurring, due to prolonged gestation length, apparent abnormality of second stage labor, or other concerns (for example, drop in rectal temperature more than 24 hours previously, bitch acting disoriented), the bitch should be evaluated with a physical examination, digital vaginal examination, and lateral abdominal radiograph to determine physical and mental status of the bitch and to determine number and position of pups present. If there is a concern about fetal viability, abdominal ultrasound should be performed. Consistent fetal heart rate of < 150 beats per minutes is indicative of fetal distress and suggests immediate surgical intervention.
Manipulation of puppies for vaginal delivery can be performed in dogs but is difficult due to size considerations. Care should be taken when manipulating puppies since they are extremely fragile. The most common medical therapy, recommended only for bitches with no signs of systemic illness that are known to have pups of a size suitable for vaginal delivery, is oxytocin. Boluses containing 2-5 IU oxytocin should be given every 20-30 minutes; if there is no response after 3 doses, no more should be given because the receptors of oxytocin on the uterus are filled and no further response is likely, and because oxytocin can cause placental separation and so should not be given without surgical intervention (Cesarean section) always at the ready. Cesarean section is recommended if the bitch is showing signs of systemic illness, the litter is very large, one or more of the pups is so large as to preclude vaginal delivery, or the bitch has not responded to medical therapy.
"My breeder says my dog has pyometriosis and has to be spayed. Is this true?" – What is pyometra and how is it best treated?
Pyometra is a uterine disease of bitches, most commonly seen in older intact females that have gone through many heat cycles. The normal hormonal changes of heat cause a gradual change in the lining of the uterus of bitches, called cystic endometrial hyperplasia. This abnormal uterine lining is predisposed to infection, allowing normal vaginal flora that move through the open cervix during proestrus and estrus to more readily colonize the uterus. During diestrus, the uterus is under the influence of progesterone, a hormone that increases secretion from uterine glands and decreases uterine contractility, allowing the bacteria to grow rapidly without being expelled from the uterus. Clinical signs usually become apparent 4-12 weeks after heat and vary with patency of the cervix. If the cervix is open, discharge of foul-smelling, pale red, thick discharge is the most obvious clinical sign. Bitches with open-cervix pyometra usually do not show severe systemic signs of illness but may have an immature neutrophilia, fever, and a palpably enlarged uterus. Bitches with closed-cervix pyometra usually do show more severe signs of systemic illness, including abdominal distension, depression, polyuria / polydipsia due to secondary renal disease, an immature neutrophilia, and grossly enlarged uterus. Diagnosis of pyometra requires verification of uterine enlargement and infection, and is accomplished with radiographs or ultrasound, and a complete blood count. Preferred treatment for either open- or closed-cervix pyometra is OHE. In my opinion, no other ethical treatment option exists for bitches with closed-cervix pyometra. Medical therapy can be tried in bitches with open-cervix pyometra if they are still of breeding age, are valuable in a breeding program, and are not azotemic. The therapy most commonly used in the United States is concurrent treatment with antibiotics and PGF2alpha. Dogs treated medically for pyometra are predisposed to pyometra after each ensuing heat cycle and so should be bred at the first heat cycle after treatment, and spayed as soon as their breeding life is over.
"My puppy only has one testicle. Can I still show him?" – What is cryptorchidism and what is its clinical significance?
Cryptorchidism is a hereditary disorder, more common in purebred than in crossbred dogs, in which one or both testes do not descend into the scrotum by 6 months of age. Monorchidism, development of only one testis, has not been reported in the dog and is considered very rare. During embryonic development, the testes develop in the abdomen, caudal to the kidneys. Descent through the inguinal canal and into the scrotum occurs in most dogs by birth but may be delayed in normal dogs. The inguinal canal is closed in most breeds of dog by 6 months of age, precluding further movement of the testes. Diagnosis is by physical examination. Retained testes are too small to be seen ultrasonographically so we often are unable to determine if a retained testis is in the inguinal area or the abdomen. Castration is the treatment of choice; the retained testis is predisposed to neoplasia and torsion of the spermatic cord, and the descended testis should be removed to prevent procreation of an animal with a hereditary defect. Medical treatment for cyrptorchidism (injection of testosterone, or gonadotropin releasing hormone (GnRH) or human chorionic gonadotropin (hCG) to cause testosterone release) has not been shown to work consistently, and is considered unethical by this author. Cryptorchid dogs cannot be shown in AKC-sanctioned conformation dog shows.
"Is it normal for spayed female cats to act like they're in heat sometimes?" – What is ovarian remnant syndrome?
Resumption of apparent normal estrous cycling in a female cat that had undergone OHE is not normal and is most commonly due to ovarian remnant syndrome. Revascularization of ovarian tissue after surgery with development of follicles, secretion of estrogen, and subsequent behaviors of heat can occur anytime from months to years after OHE. Because of the ease of feline OHE, it has been hypothesized that cats that develop ovarian remnant syndrome have inapparent masses of ovarian tissue deep in the broad ligament that are not seen and removed during routine OHE. Diagnosis is by observation of signs of estrus (monotonous yowling, lordosis [elevation of the hindquarters with lateral deviation of the tail], increased affection); cornified vaginal cytology; and successful induction of ovulation. The cat should be seen while the owner perceives it to be showing signs of heat. A vaginal swab specimen containing cornified cells verifies presence of estrogen-secreting tissue, most likely a follicle. At that time, gonadotropin releasing hormone (GnRH; 25 mcg IM) can be administered to induce ovulation of the putative follicle. Serum progesterone concentration should be assessed 2 weeks later. Serum progesterone of > 2 ng/ml is indicative of luteinized tissue on the remnant. Exploratory laparotomy can be performed at that time to find the remnant containing the corpora lutea (CLs) that form after ovulation. It is much easier to find ovarian remnants if exploratory surgery is performed when there is some sort of structure, such as a CL, on that tissue. Remnants virtually always are found at one or both ovarian pedicles. Medical estrus suppression is not a viable alternative for surgery; there are no safe estrus-suppressing drugs available for cats in the United States.
"My neutered male cat is very aggressive and is spraying urine. Is this a behavioral problem?" – What physical finding is indicative of elevated serum testosterone in male cats?"
Aggressive behavior and urine spraying are more common in intact than in castrated male cats. Diagnosis must differentiate a physical cause for the animal's change in behavior from a behavioral cause. Physical causes include conditions causing secretion of testosterone, including retention of a testis and adrenal neoplasia. A simple test on physical examination for elevated testosterone in cats is extrusion of the penis. Cats under the influence of testosterone have rings of cornified papillae surrounding their penis; these spines are lost within 6 weeks of castration.
References available on request.