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Pseudopregnancy
Pseudopregnancy
411
RABBITS
Pseudopregnancy BASIC INFORMATION Pseudopregnancy is the development of signs of pregnancy without the presence of an implanted embryo or fetus. Characteristics and behaviors can vary, ranging from a mild change in behavior to nest building—the hallmark maternal sign of impending parturition. Duration of pseudopregnancy is estimated at between 15 and 18 days post ovulation and is related to the hormonal influence of persistent corpora lutea. Hallmark signs are seen at the end of a pseudopregnancy.
SYNONYMS Pseudocyesis, false pregnancy, phantom pregnancy
EPIDEMIOLOGY SPECIES, AGE, SEX • Rabbits are induced ovulators and require the stimulation of coitus to ovulate. • Ovulation in the absence of coitus and subsequent pseudopregnancy can result from: Stimulation caused when one doe mounts another A doe mounts the young in her own litter Stressful situations (e.g., transportation in carrier to veterinarian, overnight hospitalization). A companion rabbit minimizes stress. GENETICS AND BREED PREDISPOSITION • Pseudopregnancy is rare in wild rabbits. • Pseudopregnancy can occur in 20% of does group-housed compared with single-housed does. RISK FACTORS • Any intact female doe is at risk, even singly kept animals. • Unfertilized ovulation resulting in pseudopregnancy can occur in 20% to 30% of artificially inseminated does injected with gonadotropin-releasing hormone (GnRH). GEOGRAPHY AND SEASONALITY Pseudopregnancy occurs during the breeding season. The wild European rabbit (Oryctolagus cuniculus) has a sharply defined main breeding season. In the northern hemisphere, the highest conception rate occurs in spring and the lowest in autumn, although sporadic breeding occurs during other months of the year. The breeding season of
CLINICAL PRESENTATION HISTORY, CHIEF COMPLAINT • Clients may describe: History of recent introduction of male rabbit to group of rabbits Observation of mounting on pseudopregnant rabbit by other females • Pseudopregnant rabbits can present with: Reproductive problems: Breeding animals can present with failure to mate. Rejection of buck during introduced mating sessions Enlarged and well-developed mammary glands with milk production Behavioral problems (see Dermatopathies): Unexplained aggression or behavioral changes (e.g., biting, barbering, thumping of hindfeet) toward owners or toward other animals within the rabbit’s social group Territorial aggression Fur pulling, which the owner may perceive as self-mutilation Building of nests with fur and/or other material found in the environment Excessive digging Dermatologic problems (see Dermatopathies): Some rabbits may present for patchy alopecia predominantly in the area of the dewlap and ventrum. Gastrointestinal problems:
Pseudopregnant does can present with ileus. PHYSICAL EXAM FINDINGS • A nervous and aggressive rabbit during consultation • Vital signs are often within normal limits • Mammary development that may be accompanied by lactation • Alopecia, usually around the area of the dewlap and ventrum • Absence of palpable fetuses during abdominal palpation Marble-shaped fetuses are distinguished between 12-14 days of pregnancy as they slip between thumb and fingers when gently moved back and forth with slight pressure. After 14-16 days of pregnancy distinguishing between fetuses and digestive organs is difficult. Radiographic confirmation of fetuses is possible after 11-12 days of pregnancy.
ETIOLOGY AND PATHOPHYSIOLOGY • The female rabbit is an induced ovulator: An estrous cycle does not occur, although estrus behavior is observed. Ovulation occurs after mating. Coitus provokes a reflex discharge of GnRH and hence LH from the pituitary, inducing ovulation. Behavioral estrus in rabbits is characterized by lordosis and allowing other rabbits to mount. • Ovulation can also be induced by: Rabbit-to-rabbit interaction (even in the absence of a buck) Mounting by other sexually active does or sterile bucks Close proximity or scent of male rabbits Transportation of female rabbits This is a common cause of spontaneous ovulation. • Normal gestation is 28-31 days. Hormones (primarily progesterone) secreted by the corpus luteum maintain pregnancy. After ovulation, even in the absence of fertilization and implantation, the uterus and mammary glands can still develop under the influence of the corpus luteum, which provides the hormonal influence for pseudopregnancy. • In a nonpregnant rabbit, the corpus luteum regresses after 10 to 12 days. • Pseudopregnancy lasts 15 to 18 days.
RABBITS
DEFINITION
domestic European rabbits is less sharply defined, although mating occurs more often in spring and summer than in autumn and winter. ASSOCIATED CONDITIONS AND DISORDERS • Pseudopregnancy may lead to other uterine disorders (see Uterine Disorders) such as hydrometra. • Pseudopregnancy may result in mammary gland development and milk production. Lactating rabbits may develop mastitis. • Depending on the extent of behavioral changes during pseudopregnancy, rabbit-to-rabbit aggression can occur, resulting in bite wounds and abscesses. • Mild alopecia or increased fur loss may result from maternal fur pulling and progesterone influences. Normally, the fur is tightly adhered to the skin, but during pregnancy and pseudopregnancy, it becomes loose.
• After luteolysis, progesterone levels drop rapidly and maternal behaviors become apparent. • Nest building and other maternal behaviors of the doe are controlled by a combination of hormones, including estrogen, progesterone, and prolactin.
DIAGNOSIS DIFFERENTIAL DIAGNOSIS • Late gestation • Ovarian remnant after ovariectomy/ ovariohysterectomy • Adrenal tumors producing excessive sex hormones
INITIAL DATABASE Signalment, examination
history,
and
physical
ADVANCED OR CONFIRMATORY TESTING • Abdominal radiography and ultrasound to rule out presence of fetuses • Progesterone levels or hormonal panels can be measured: Hormone measurements must be validated at the testing laboratory. Hormone levels must be interpreted in relation to the behavior of the doe. Pregnant and pseudopregnant rabbits cannot be differentiated accurately until day 19 of pregnancy/ pseudopregnancy.
TREATMENT THERAPEUTIC GOAL Elimination of future occurrences of pseudopregnancy
ACUTE GENERAL TREATMENT • Treatment is unnecessary in most cases because pseudopregnancy is self-limiting. • One injection of prostaglandin PGF2α (e.g., 200 µg alfaprostol SC) on the 10th or 11th day has been used in research laboratories and breeding farms to terminate pseudopregnancy. The doe can then be fertilized 14 days after an earlier infertile insemination. Without prostaglandin treatment, the doe cannot be fertilized again until 21 days after an infertile insemination. Use of prostaglandin PGF2α is not recommended in pet rabbits. However, its use can be considered when extreme nesting behavior is refractory to treatment.
CHRONIC TREATMENT
pregnancy or pseudopregnancy, the female plucks fur from her body (chiefly from her dewlap and ventrum) and uses this to line the nest. This is called the maternal nest. This nest is built only under the condition of pregnancy or pseudopregnancy, or with appropriate experimental manipulations involving the hormones of pregnancy. Pregnant does generally keep a maternal nest free of feces and urine, whereas pseudopregnant does will fail to keep a maternal nest clean. • Use of synthetic progesterone or androgens to terminate a pseudopregnancy is currently unproven and is restricted to research laboratory conditions.
PREVENTION
The treatment of choice is neutering.
Pseudopregnancy neutering.
RECOMMENDED MONITORING
CLIENT EDUCATION
Because of the increasing incidence of uterine disorders with age, intact female rabbits should be assessed frequently.
• Pseudopregnancy often recurs and can be prevented by neutering. • Potential uterine disorders can be prevented by neutering.
PROGNOSIS AND OUTCOME Prognosis is good because the condition is self-limiting.
PEARLS & CONSIDERATIONS COMMENTS • The core event in maternal behavior is construction of the maternal nest. Initially, the doe builds a nest of straw, hay, or other such material (described as the “straw nest”). At the end of
is
prevented
by
SUGGESTED READING Gonzalez-Mariscal G, et al: Maternal care of rabbits in the lab and on the farm: endocrine regulation of behavior and productivity, Horm Behav 52:86–91, 2007.
CROSS-REFERENCES TO OTHER SECTIONS Behavioral Disorders Dermatopathies Mammary Gland Disorders Uterine Disorders AUTHOR: CATHY T.T. CHAN EDITOR: DAVID VELLA
411
RABBITS
Pseudopregnancy BASIC INFORMATION Pseudopregnancy is the development of signs of pregnancy without the presence of an implanted embryo or fetus. Characteristics and behaviors can vary, ranging from a mild change in behavior to nest building—the hallmark maternal sign of impending parturition. Duration of pseudopregnancy is estimated at between 15 and 18 days post ovulation and is related to the hormonal influence of persistent corpora lutea. Hallmark signs are seen at the end of a pseudopregnancy.
SYNONYMS Pseudocyesis, false pregnancy, phantom pregnancy
EPIDEMIOLOGY SPECIES, AGE, SEX • Rabbits are induced ovulators and require the stimulation of coitus to ovulate. • Ovulation in the absence of coitus and subsequent pseudopregnancy can result from: Stimulation caused when one doe mounts another A doe mounts the young in her own litter Stressful situations (e.g., transportation in carrier to veterinarian, overnight hospitalization). A companion rabbit minimizes stress. GENETICS AND BREED PREDISPOSITION • Pseudopregnancy is rare in wild rabbits. • Pseudopregnancy can occur in 20% of does group-housed compared with single-housed does. RISK FACTORS • Any intact female doe is at risk, even singly kept animals. • Unfertilized ovulation resulting in pseudopregnancy can occur in 20% to 30% of artificially inseminated does injected with gonadotropin-releasing hormone (GnRH). GEOGRAPHY AND SEASONALITY Pseudopregnancy occurs during the breeding season. The wild European rabbit (Oryctolagus cuniculus) has a sharply defined main breeding season. In the northern hemisphere, the highest conception rate occurs in spring and the lowest in autumn, although sporadic breeding occurs during other months of the year. The breeding season of
CLINICAL PRESENTATION HISTORY, CHIEF COMPLAINT • Clients may describe: History of recent introduction of male rabbit to group of rabbits Observation of mounting on pseudopregnant rabbit by other females • Pseudopregnant rabbits can present with: Reproductive problems: Breeding animals can present with failure to mate. Rejection of buck during introduced mating sessions Enlarged and well-developed mammary glands with milk production Behavioral problems (see Dermatopathies): Unexplained aggression or behavioral changes (e.g., biting, barbering, thumping of hindfeet) toward owners or toward other animals within the rabbit’s social group Territorial aggression Fur pulling, which the owner may perceive as self-mutilation Building of nests with fur and/or other material found in the environment Excessive digging Dermatologic problems (see Dermatopathies): Some rabbits may present for patchy alopecia predominantly in the area of the dewlap and ventrum. Gastrointestinal problems:
Pseudopregnant does can present with ileus. PHYSICAL EXAM FINDINGS • A nervous and aggressive rabbit during consultation • Vital signs are often within normal limits • Mammary development that may be accompanied by lactation • Alopecia, usually around the area of the dewlap and ventrum • Absence of palpable fetuses during abdominal palpation Marble-shaped fetuses are distinguished between 12-14 days of pregnancy as they slip between thumb and fingers when gently moved back and forth with slight pressure. After 14-16 days of pregnancy distinguishing between fetuses and digestive organs is difficult. Radiographic confirmation of fetuses is possible after 11-12 days of pregnancy.
ETIOLOGY AND PATHOPHYSIOLOGY • The female rabbit is an induced ovulator: An estrous cycle does not occur, although estrus behavior is observed. Ovulation occurs after mating. Coitus provokes a reflex discharge of GnRH and hence LH from the pituitary, inducing ovulation. Behavioral estrus in rabbits is characterized by lordosis and allowing other rabbits to mount. • Ovulation can also be induced by: Rabbit-to-rabbit interaction (even in the absence of a buck) Mounting by other sexually active does or sterile bucks Close proximity or scent of male rabbits Transportation of female rabbits This is a common cause of spontaneous ovulation. • Normal gestation is 28-31 days. Hormones (primarily progesterone) secreted by the corpus luteum maintain pregnancy. After ovulation, even in the absence of fertilization and implantation, the uterus and mammary glands can still develop under the influence of the corpus luteum, which provides the hormonal influence for pseudopregnancy. • In a nonpregnant rabbit, the corpus luteum regresses after 10 to 12 days. • Pseudopregnancy lasts 15 to 18 days.
RABBITS
DEFINITION
domestic European rabbits is less sharply defined, although mating occurs more often in spring and summer than in autumn and winter. ASSOCIATED CONDITIONS AND DISORDERS • Pseudopregnancy may lead to other uterine disorders (see Uterine Disorders) such as hydrometra. • Pseudopregnancy may result in mammary gland development and milk production. Lactating rabbits may develop mastitis. • Depending on the extent of behavioral changes during pseudopregnancy, rabbit-to-rabbit aggression can occur, resulting in bite wounds and abscesses. • Mild alopecia or increased fur loss may result from maternal fur pulling and progesterone influences. Normally, the fur is tightly adhered to the skin, but during pregnancy and pseudopregnancy, it becomes loose.
• After luteolysis, progesterone levels drop rapidly and maternal behaviors become apparent. • Nest building and other maternal behaviors of the doe are controlled by a combination of hormones, including estrogen, progesterone, and prolactin.
DIAGNOSIS DIFFERENTIAL DIAGNOSIS • Late gestation • Ovarian remnant after ovariectomy/ ovariohysterectomy • Adrenal tumors producing excessive sex hormones
INITIAL DATABASE Signalment, examination
history,
and
physical
ADVANCED OR CONFIRMATORY TESTING • Abdominal radiography and ultrasound to rule out presence of fetuses • Progesterone levels or hormonal panels can be measured: Hormone measurements must be validated at the testing laboratory. Hormone levels must be interpreted in relation to the behavior of the doe. Pregnant and pseudopregnant rabbits cannot be differentiated accurately until day 19 of pregnancy/ pseudopregnancy.
TREATMENT THERAPEUTIC GOAL Elimination of future occurrences of pseudopregnancy
ACUTE GENERAL TREATMENT • Treatment is unnecessary in most cases because pseudopregnancy is self-limiting. • One injection of prostaglandin PGF2α (e.g., 200 µg alfaprostol SC) on the 10th or 11th day has been used in research laboratories and breeding farms to terminate pseudopregnancy. The doe can then be fertilized 14 days after an earlier infertile insemination. Without prostaglandin treatment, the doe cannot be fertilized again until 21 days after an infertile insemination. Use of prostaglandin PGF2α is not recommended in pet rabbits. However, its use can be considered when extreme nesting behavior is refractory to treatment.
CHRONIC TREATMENT
pregnancy or pseudopregnancy, the female plucks fur from her body (chiefly from her dewlap and ventrum) and uses this to line the nest. This is called the maternal nest. This nest is built only under the condition of pregnancy or pseudopregnancy, or with appropriate experimental manipulations involving the hormones of pregnancy. Pregnant does generally keep a maternal nest free of feces and urine, whereas pseudopregnant does will fail to keep a maternal nest clean. • Use of synthetic progesterone or androgens to terminate a pseudopregnancy is currently unproven and is restricted to research laboratory conditions.
PREVENTION
The treatment of choice is neutering.
Pseudopregnancy neutering.
RECOMMENDED MONITORING
CLIENT EDUCATION
Because of the increasing incidence of uterine disorders with age, intact female rabbits should be assessed frequently.
• Pseudopregnancy often recurs and can be prevented by neutering. • Potential uterine disorders can be prevented by neutering.
PROGNOSIS AND OUTCOME Prognosis is good because the condition is self-limiting.
PEARLS & CONSIDERATIONS COMMENTS • The core event in maternal behavior is construction of the maternal nest. Initially, the doe builds a nest of straw, hay, or other such material (described as the “straw nest”). At the end of
is
prevented
by
SUGGESTED READING Gonzalez-Mariscal G, et al: Maternal care of rabbits in the lab and on the farm: endocrine regulation of behavior and productivity, Horm Behav 52:86–91, 2007.
CROSS-REFERENCES TO OTHER SECTIONS Behavioral Disorders Dermatopathies Mammary Gland Disorders Uterine Disorders AUTHOR: CATHY T.T. CHAN EDITOR: DAVID VELLA