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Apparent infertility in the
bitch may actually be a manifestation of underlying problems. Dr. Margret
Casal, assistant professor of medical genetics at the School, discussed
reproductive problems in the bitch that impair fertility or otherwise
hamper successful matings.
January 27, 2001
31st Canine Symposium
VHUP, Philadelphia
The number one reason for matings to be unsuccessful is that the bitch was
bred on the wrong day of her cycle. On the other hand, some bitches fail to
get pregnant because they are altogether acyclic. Acyclic bitches either
have not experienced their first heat for reasons like delayed puberty or
breed idiosyncrasies (large-breed dogs, for example, tend to begin cycling
at a later age than do small-breed dogs), or they have ceased their heat
cycles due to disease such as ovarian cysts or tumors.
Other disturbances in the heat cycle can occur, said Dr. Casal. These
include prolonged proestrus, prolonged estrus and split estrus. Bitches in
prolonged proestrus often must be "pushed into ovulating" using
hormone therapy. Prolonged estrus phases--which last more than 12 days--are
sometimes anovulatory. Hormone therapy to treat prolonged estrus may result
in marked side effects. Split estrus is characterized by a normal proestrus
and the beginning of an apparently normal estrus in which the female
initially allows mounting, then refuses, and then allows it again. Vaginal
cytology often reveals that the bitch was not in true estrus until the
second standing heat. These cycle anomalies cause difficulty in timing
breeding.
Infections can also lead to the appearance of infertility in the bitch or
the stud dog. Infections with Brucella canis or canine herpesvirus can
cause early abortions. These aborted pregnancies, which often go unnoticed,
may be mistaken for barren cycles. Mycoplasma has also been implicated as a
cause for infertility. E. coli, Staphylococcus and Streptococcus are often
associated with pyometra, another cause for infertility. Most bacterial
infections are diagnosed by culturing vaginal secretions; a diagnosis of
brucellosis or herpes infection is made by blood culture and/or by lymph
node biopsies.
Other frequent medical barriers to reproduction in dogs include
hypothyroidism, obesity, malnutrition and congenital defects. Vaginal
hyperplasia and malformations may lead to reluctance to be bred, which
gives the semblance of infertility. Abnormalities of sexual
differentiation--in either chromosomal sex, gonadal sex and phenotypic
sex--may also impair fertility. Many of these are breed related, such as
pseudohermaphrodism in the miniature schnauzer.
Reproductive Problems in Male Dogs
Male infertility typically stems from primary defects in the sperm cells,
which can result from a number of disease processes. Dr. Cynthia Ward,
assistant professor of medicine at the School, reviewed semen evaluation
procedures in dogs and discussed diseases of the prostate that can impair
fertility.
"All infertility exams should involve semen collection and
evaluation," said Dr. Ward.
Semen samples can readily be obtained from experienced stud dogs. Three
semen fractions are present: clear pre-sperm fluid, sperm-rich fluid, and
prostatic secretions. The sperm-rich fraction should be evaluated for sperm
count, motility, morphology and cytology. Sperm motility should be examined
promptly, as it decreases as the semen cools. The percentage of sperm
swimming rapidly forward should be estimated from at least four different
places on the slide, and the presence of sperm agglutination--which is
associated with such causes of infertility as Brucella and anti-sperm
antibody--noted. Normal dogs should have at least 200 million sperm per
ejaculate. If consistently poor sperm motility is observed, infectious
and/or inflammatory causes should be considered.
Sperm morphology is evaluated under staining. Generally, at least 75
percent of the sperm cells should be morphologically normal. The presence
of white blood cells--especially degenerated ones, or red blood cells, may
signal infection and/or inflammation. If infection is suspected, a semen
sample should be cultured for aerobic bacteria.
The third semen fraction, which consists mainly of prostatic secretions,
should be examined cytologically, said Dr. Ward. The presence of large
numbers of bacteria , or red/white blood cells, may signal infection and/or
inflammation.
"I and others believe there's a lot of subclinical infertility caused
by chronic prostatic disease," she explained. "Maybe we should be
looking at the prostate more and more carefully when we're trying to
diagnose some types of infertility in male dogs."
Prostatitis and prostatic abscesses can cause infertility in dogs. Both
conditions are infectious in etiology. E. coli is the most common organism
isolated, although others, such as Brucella canis, have also been found.
Approximately ten percent of affected dogs have concurrent urinary tract
infections. A dog with acute prostatitis is often systemically ill. A
stilted gait, caudal abdominal pain and urethral discharge may be present.
Ejaculation is painful, and these dogs may be reluctant to breed. Prostatic
infection may spread hematogenously to other organs and, in chronic cases,
may also cause infertility because sperm do not thrive in the presence of
inflammatory mediators. Diagnosis is made by hematology, urinalysis, urine
culture, or culture and cytology of semen or prostatic fluid. Prostatic
infections are treated with antibiotics for four to six weeks, and
castration is indicated in refractory cases.
Another common prostatic disease is benign prostatic hyperplasia (BPH), an
age-related change occurring in people and dogs. BPH is a benign increase
in the number and size of prostatic epithelial cells. Although BPH occurs
in every aging dog, they don't all manifest the clinical signs of urethral
discharge, hematuria, and tenesmus. BPH is diagnosed by clinical signs,
physical exam, radiographs or ultrasound, hematology, urinalysis and
prostatic fluid analysis. Castration is the treatment of choice for BPH,
although the drug finasteride, an androgen antagonist, can be used to help
decrease the proliferation of prostatic cells.
A far more serious affliction than BPH, prostatic neoplasia accounts for
about five percent of all prostatic diseases. Occurring with equal
frequency in intact and neutered males, prostatic neoplasia most commonly
takes the form of adenocarcinoma, followed by transitional cell carcinoma.
Prostatic neoplasia carry grave prognoses.
Advantages and Disadvantages of Using Fresh-Chilled or Frozen Semen
Creating the "choice" pup today is possible without ever having
the "choice" parents in each other's presence. Dr. Melissa
Goodman, a reproduction specialist who maintains a specialty veterinary
practice at the Veterinary Referral Center in Frazer, Pennsylvania,
presented the pros and cons of remote reproduction via frozen or chilled
semen shipments.
By employing sophisticated technology available for obtaining, processing
and using chilled or frozen semen, one can greatly increase the gene pool
available for matings. These reproductive methods also enable breeders and
owners to achieve pregnancies without shipping the bitch or stud dog or
hosting the bitch. Yet the added convenience and versatility of these
technologies comes with tradeoffs, explained Dr. Goodman.
While the use of chilled semen eliminate limitations of geography, it
introduces limitations of time: Although semen extenders provide the cells
with a nutrient source and protection during transport, the life span of
the sperm is greatly reduced, necessitating that the stud be available at
the time the bitch is ovulating.
Furthermore, said Dr. Goodman, "Whenever we process sperm--chilling,
shipping, freezing and thawing--we are damaging it. So, by definition, we
will always decrease fertility whenever we use these procedures."
To obtain a high-quality ejaculate, the semen collection process must be
performed with care and foresight. Since, at best, ten percent of the
ejaculate is lost during collection, processing and shipping, Dr. Goodman
recommends that only dogs with normal ejaculates (normal sperm count and
motility) be used. The quantity and quality of semen produced in an
ejaculate are affected by the dog's age, size, breed and general health
status. Some medications and recent ejaculation may also affect semen
quality. A period of sexual rest of 10-14 days is suggested before
ejaculation to maximize the sperm count. Libido, which also affects the
quality of the ejaculate, can be heightened by an experienced collector and
the presence of a teaser bitch.
Following collection, the ejaculate--which contains three fractions--should
be separated, and only the sperm-rich fraction used.
The use of chilled semen requires skillful choreography. Because the sperm
begins to degrade immediately after ejaculation, insemination should be
performed within 24 hours of collection. Therefore, the schedules of the
stud owner, bitch owner, collecting veterinarian and inseminating
veterinarian must be coordinated, and shipping arrangements must be made in
advance.
Accurate ovulation timing is crucial to the success of chilled semen
breeding. The stress of chilling and shipping reduces the life span of the
sperm cells from about 5-7 days to just 2-4 days. Inseminations must be
performed during the bitch's 72-hour fertile period. The most accurate
indicator of ovulation and the fertile period is the luteinizing hormone
(LH) surge, which is best identified by a combination of blood assays for
LH and progesterone, as well as vaginal cytology and vaginoscopy. Dr.
Goodman advocates two inseminations, usually on days four and six post-LH
surge. The average conception rate for chilled, extended semen is
approximately 80 percent.
Unlike chilled semen, frozen semen allows the genetic potential of a stud
dog to be preserved for future use, in the event of disease, death,
unexpected sterility or sale of the dog. Freezing the semen also
facilitates long-distance and international breedings, and is useful when
the stud is not available during the bitch's fertile periods. When properly
processed, frozen, and stored, canine semen will last an estimated 10,000+
years. The sample is extended with a buffer solution that protects the
sperm cells during freezing and thawing. The sample is then frozen either
in straws over liquid nitrogen or in pellets in dry ice. Storage is done in
liquid nitrogen.
For an insemination using frozen semen, only a bitch with good fertility
should be used, since the sperm quality will be compromised. Approximately
100 million progressively motile sperm are needed in order to achieve a
normal pregnancy. Therefore, post-thaw sperm count and quality should be
assessed in order to determine the number of straws to use.
Precise ovulation timing is essential, since the stress of freezing and
thawing damages the sperm membranes, shortening the life span of the thawed
sperm cells to 12-24 hours. Daily blood testing is recommended to identify
the LH surge, enabling insemination during the bitch's short fertile
period. If a frozen insemination is performed even a few hours too early,
said Dr. Goodman, "you can have high-quality frozen semen and a very
fertile bitch, but the two will pass like ships in the night."
Once thawed, the semen can be deposited into the uterus via a catheter
passed through the cervix. The most common, and perhaps most successful,
method, is a quick surgical technique that allows direct deposition of the
semen at the ends of the uterine horns, just adjacent to the oviducts.
Managing the Breeding
Most dogs that fail to conceive have normal fertility status. Dr. Matthew
Ellinwood, resident in medical genetics at the School, revealed the real
reason behind unsuccessful matings and outlined steps for enhancing
breeding success.
In cases of apparent infertility, the matings have not been accurately
synchronized with ovulation. "The biggest problem is not the dogs
having a primary infertility," said Dr. Ellinwood. "It's that
they haven't been managed properly."
Planning successful breedings requires a good understanding of the estrus
cycle. The bitch experiences her first estrus between six and 18 months of
age, with size and breed variations. The estrus cycle is divided into four
phases that are differentiated by cytologic, hormonal and behavioral
features.
The first phase, proestrus, is characterized by bloody vaginal discharge.
During proestrus--which lasts one week, on average--estrogen becomes the
dominant hormone, the uterine lining begins to proliferate, and the vaginal
epithelium starts to cornify. The next phase, estrus, spans from the point
at which the bitch willingly stands for mating to the point at which she
refuses to be bred. Estrogen levels fall and progesterone rises, the
vaginal epithelium further cornifies, and ovulation occurs. During estrus,
which lasts about a week, the bitch experiences behavioral changes that
culminate in "standing heat," or submission to breeding. Diestrus
follows, lasting 57 days in the pregnant bitch and slightly longer in the
nonpregnant bitch. During diestrus, the bitch refuses to be bred.
Progesterone dominates and the vaginal cytology changes to less than 50
percent cornified cells. Ensuing anestrus--which lasts five months, on
average--is the period from the end of the progesterone elevation to the
beginning of the next cycle.
In preparing for breeding, one should have physical exams--including
reproductive exams--performed on both the bitch and the stud dog. Routine
lab work, including a complete blood count, a serum biochemistry panel and
a urinalysis, should be done on the breeding pair, particularly the bitch.
A Brucella canis titer should be obtained on both dogs. And if either dog
has a history of infertility, vaginal and preputial cultures should be
performed.
Accurate timing of breeding is perhaps the greatest breeding success
factor. In order to detect proestrus, the bitch's vulva should be examined
once weekly beginning four-and-a-half months after the beginning of her
last cycle. After the bitch has begun to show vaginal discharge, signaling
proestrus, vaginal cytology should be done every three to four days until
she has 90 percent cornified cells (estrus). Once the bitch has reached
standing estrus, breeding should be allowed every two days for two to three
breedings. After this, breeding frequency can be decreased to once every
three or four days until the bitch refuses to be mounted.
While the behavior of the bitch and, in some cases, the stud are reliable
indicators of estrus, a bitch will occasionally refuse to stand for
breeding during estrus under any circumstances. In such cases, artificial
insemination should be considered.
In conclusion, Dr. Ellinwood recommended that owners and breeders keep
thorough records of previous cycles in order to better predict breeding
variables and plan matings. In timing breeding, these records should be
considered in tandem with vaginal cytology and behavioral cues in the bitch
and the stud.
Whelping the Litter
The complexity of the birthing process is manifest in the post-whelping
period, during which a variety of complications may arise in the dam. Dr.
Margret Casal, assistant professor of medical genetics at the School,
discussed these disorders and their clinical signs, diagnosis and
treatment.
Following whelping, uterine involution is complete four weeks postpartum,
but the uterus does not return to its anestrus histologic state until about
150 days postpartum. A bloody discharge is passed for up to 10 days to two
weeks after whelping.
Persistent heavy bleeding after whelping may indicate rupture of the blood
vessels within the uterus or the birth canal. The most common reasons for
uterine bleeding are overdoses of oxytocin and fetal extraction using
surgical instruments. Purely vaginal bloody discharge is typically caused
by trauma to the birth canal. Hemorrhage, which usually begins several days
after birth, usually occurs in the morning when the bitch arises. Bleeding
from damaged vessels in the birth canal can be controlled with tamponage
or, in the case of larger vessels, surgical repair. Uterine hemorrhage is
usually controlled with pregnancy hormones. If blood loss is extensive,
transfusion may be necessary.
Metritis--inflammation of the uterus--may also occur postpartum. Metritis
is the result of bacterial invasion into the uterus secondary to abortion,
fetal infection, manipulation during whelping, placental retention or
ascending infection. Bitches with metritis typically neglect their pups.
Diagnosis is made by ultrasound and vaginal smears. If not treated
promptly, metritis can lead to more serious conditions, such as pyometra
and sepsis. Treatment includes antibiotics, oxytocin and prostaglandins.
In a bitch with retained placenta, the discharge may also contain necrotic
particles. Clinical signs are fever and persistent greenish-black, watery,
foul-smelling discharge. Diagnosis is made by digital palpation,
vaginoscopy or ultrasound. Placental retention is treated with oxytocin and
prostaglandins.
Uterine prolapse--protrusion of parts or all of the uterus through the
vulva, occurs typically after the birth of the last pup. Rapid
repositioning of the uterus is critical to preventing tissue necrosis, an
indication for immediate spaying.
Subinvolution of placental sites (SIPS), a condition wherein the sites of
placental attachment do not revert to their normal, nonpregnant state,
occurs occasionally in bitches younger than 2.5 years of age. Affected
bitches present with persistent, serosanguinous, odorless vaginal
discharge. Diagnosis is made by ultrasound. Subinvolution sites normally
heal on their own; however, if necrosis becomes severe, the uterus can
rupture, requiring immediate surgery.
A common finding in bitches producing copious amounts of milk, eclampsia
ensues when heavy lactation depletes the bitch's calcium reserve. Eclampsia
is seen at the height of lactation (2-3 weeks after whelping), and occurs
more commonly in small- than large-breed dogs. Clinical signs include
restlessness, muscle tremors, increased respiratory rate and, eventually,
stiff gait, high fever (>104F) and convulsions. Therapy consists of
intravenous calcium and if needed sodium bicarbonate and glucose. Following
initial treatment, the bitch is sent home with calcium and vitamin D3 to
prevent further occurrences.
Mastitis is a condition in which one or more mammary gland are enlarged,
hot and red due to bacterial invasion by E. coli, Staphylococcus or
Streptococcus. The affected bitch is typically febrile, anorexic and
neglects her pups. The milk may be rancid. Pups should be prevented from
suckling on affected teats. Abscesses are drained and adjunct treatment
consists of antibiotics and warm compresses. Severe mastitis may warrant
surgical removal of affected glands.
Occasionally, milk may not be expressed from the bitch's mammary gland. To
test if she is not "letting down" the milk or if she is actually
not producing any (agalactia) a single dose of oxytocin on the tongue will
cause letdown if milk is being produced. Absence of milk production is an
untreatable condition, and pups will need to be provided an alternate
source of nutrition.
Chronism, or postpartum hysteria, is a breed-specific condition in which
the bitch mutilates her normal pups. Occasionally, chronism is manifest as
excessive grooming of the pups, abrading the skin off of them.
Stillborn and Fading Puppies: What Can They Tell Us?
For owner and breeder alike, a dead pup is a heartbreak. But it is also a
medical opportunity. The information veterinarians can glean from a pup
that has died in utero or neonatally is paramount to preventing illness and
reducing the likelihood of congenital defects in future generations.
"If you have a large litter and several of the pups die, you want them
treated as a litter. Therefore, the health of that litter is dependent upon
knowing what went wrong with the animals that haven't survived," said
Dr. Mark Haskins, professor of pathology at the School, who lectured on
neonatal and pediatric pathology in dogs.
The importance of the autopsy in this age group is underscored by the
statistics: among purebred dogs, ten percent are stillborn or die before
their first veterinary examination and nearly 20 percent die within the
first week of life. Overall pre-weaning mortality is 30 to 45 percent.
If a pup dies abruptly, the two major concerns are infection and genetic
defects. The former puts the surviving litter mates at risk; the latter,
future generations. Autopsy data can be used to protect these two groups of
pups, although pathology is not a perfect science. The clinical signs of "fading puppy syndrome," a term that describes a variety of
conditions in which pups that are apparently normal at birth gradually
weaken and die, are very nonspecific. Many of these pups suffer inborn
errors of metabolism, which are difficult to diagnose, explained Dr.
Haskins.
"The majority of the time, they're going to come back to you and say,
'I don't know why the puppy died.'"
The autopsy of the pup differs in many ways from that of the adult dog. In
the pup, the skeletal muscle is comparatively paler in color, and adipose
tissue is light brown and relatively sparse. The thymus, which regresses
with age, is still prominent. Ossification is limited, and the brain and
kidneys are still in the process of maturation.
Such differences are taken into account when detecting for the presence of
developmental malformations, which are a major concern in neonatal
pathology. Malformations have been reported in seven to 20 percent of
neonatal deaths in dogs and cats. Congenital malformations take many
different forms, from duplications to arrested development (aplasia or
hypoplasia), failure to regress (imperforation), and failure to close
(persistent patency)--as in the case of cleft palate, diaphragmatic hernia
and neural tube defects.
At the molecular level, developmental malformations are caused by
alterations in DNA structure and nucleic acid function, altered energy
states, changed membranes and enzyme inhibition. The most sensitive period
for the occurrence of these anomalies is the first trimester (days
1-20)--the period of organ formation. The underlying causes for these
molecular alterations are biological agents (i.e., viruses, bacteria and
fungi), physical agents (i.e., ionizing radiation), chemical agents (i.e.,
certain drugs) and inherited genetic defects.
Less significant in dogs than developmental malformations, prematurity is
manifest primarily as immaturity of the mature surfactant system that
facilitates expansion of the lungs. Prematurity is a diagnostic challenge
in dogs because of the great variation in size between breeds.
Mortality in neonatal pups can also be directly caused by infectious
agents, such as herpesvirus, parvovirus, adenovirus (infectious canine
hepatitis), paramyxovirus (canine distemper), bacterial infections (group B
Streptococcus and E. coli) and trauma.
Neonatal and Pediatric Care
Neonates require special care during their precarious first weeks of life.
Dr. John Melniczek, lecturer in medical genetics at the School, discussed
early postnatal development and care in pups.
The most stressful period in a pup's life is the first week of age, which
is the interval of highest mortality; weaning is the second most stressful
time. The breeder can help a pup cope with stressors by examining it
shortly after birth to detect for the presence of any obvious congenital
defects, which may impair development and hinder survival. Some of the more
common congenital abnormalities in pups are cleft palate, open anterior
fontanel, hydrocephalus, heart disease, umbilical hernia and inborn errors
of metabolism.
Within hours after birth, the pup should begin to consume colostrum, which
is the source for over 90 percent of the maternal antibodies the pup
receives. Prior to breeding, the bitch should have been brought up to date
on her vaccinations, thereby maximizing the presence of maternal antibodies
in her colostrum.
Because of their immature glucose storage systems and renal function, pups
are prone to hypoglycemia and dehydration. Hence, adequate nutrition is
critically important. The pup's growth rate is a sensitive indicator of
nutritional status. Pups should be weighed daily for the first three weeks
of life, during which time it gains about ten percent of its body weight
daily. If weight gain is inadequate, the dam's mammary glands should be
expressed to ensure adequate milk production, and her nursing behavior
should be observed. Supplementation with milk replacers and bitches' milk
should be considered in cases of poor weight gain. In nursing pups, weaning
can begin at three to four weeks of age, but should not be completed until
six weeks.
Neonates also have undeveloped thermoregulatory systems. Because of their
large surface area-to-body mass ratio, sparse body fat, high water
composition, poor blood flow to the extremities, and immature shivering and
panting responses, pups have difficulty regulating their body temperatures.
During the first weeks of life, the ambient temperature in the nesting area
should be kept at 86-90F, with gradual reductions to 75F over the next
three weeks. Maintaining normal body temperature--which is 96-97F during
the first two weeks of life, and increases to 100F by four weeks of age--is
important for normal function of the pup's metabolic pathways. Normal body
temperature is also a deterrent to infectious diseases, many of which grow
best at low body temperatures.
Neonates can fall prey to a variety of infectious agents. Canine
herpesvirus, most common in pups under three weeks of age, can cause
depression, diarrhea, respiratory disease and sudden death. If contracted
during pregnancy, it can cause abortion. Affected pups should be kept warm
and well hydrated, and any electrolyte imbalances should be corrected.
Although no vaccine is available, an affected dam's subsequent litters are
usually immune if they've received adequate colostrum.
Canine parvovirus type 1, seen primarily in pups aged 5-21 days, causes
diarrhea, pneumonia and death, as well as abortion and infertility in
infected bitches. Like canine herpesvirus, treatment is symptomatic and no
vaccine is available.
Pups of all ages are subject to bacterial infections. "The young
animal is prone to these because the immune system is not yet what it
should be," said Dr. Melniczek. Pups can develop bacterial respiratory
infections through aspiration secondary to cleft palate, vomiting or
regurgitation. Kennel cough, caused by Bordetella bronchiseptica, is also
frequently seen in neonates. Puppy pyoderma, usually caused by
Staphylococcus, is a common skin affliction in pups.
Vomiting and diarrhea is often seen in pups aged three to five weeks. Usual
etiologies in the pup are parasites (roundworms and hookworms), Coccidia,
Campylobacter, Clostridia, Salmonella, distemper, metabolic disease (i.e.,
liver shunt) and dietary indiscretion.
Genetic diseases cause a variety of syndromes in pups, such as cystinuria
in the Newfoundland, copper toxicosis in the Bedlington terrier and
phosphofructokinase deficiency in the English Springer Spaniel. Sensitive
metabolic screens and genetic tests for the identification of affected and
carrier animals have been developed at the School. J.C.
January 27, 2001
Canine Reproduction
31st Canine Symposium
VHUP, Philadelphia |
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