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Estrus Suppression, Sterilization, and Pregnancy Termination
11 Estrus Suppression, Sterilization, and Pregnancy Termination FREQUENTLY ASKED QUESTIONS 1) I want my hunting dog to be in heat in the spring so I can breed her and have her back in shape by hunting season in the fall. I expect her to be in heat in February. Is there a drug you can give to delay her heat for a couple of months? The only approved drug available for suppression of heat does not allow us to time when a dog is likely to come into heat. We could try suppressing this heat and then inducing heat in the spring, but the success rate using this technique is not 100%.
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2) I think my dog got bred by accident. Can you do a vaginal examination to determine whether sperm are present? If there are spermatozoa visible on a vaginal swab, you know she got bred; if no spermatozoa are visible, that does not mean she did not get bred, however. 3) My dog just got bred by accident. What do I do now? There is one drug for pregnancy termination that is given at the time the dog was bred (estrogen). This drug has reproductive side effects and is not my drug of choice. I prefer to wait to see whether the dog is pregnant first by checking her 30 days after the accidental breeding. If she is not pregnant, great! If she is, we safely can terminate the pregnancy at that time.
I.
ESTRUS SUPPRESSION Suppression of estrus or heat may be attempted when a bitch is to be shown in obedience, worked in the field with male dogs, or otherwise is at a point where the physical and behavioral changes of heat would be disadvantageous for her or other dogs. Estrus suppression does not allow one to put off heat for a specific period; for example, one cannot use estrus-suppressing drugs to make sure a dog will cycle in a specific month. Estrus-suppressing drugs should be administered only if the owner is sure the dog will be bred in the future. Sterilization by ovariohysterectomy (OHE) is the preferred technique for the vast majority of female dogs in the United States.
A.
PROGESTOGENS The only estrus-suppressing agent approved for use in breeding bitches in the United States is the progestogen megestrol acetate (Ovaban). The drug can be used either during anestrus or within the first 3 days of proestrus. If administered during anestrus, the drug is given at a low dose daily for 32 days. If given within the first 3 days of proestrus, the drug is administered for 8 days at a higher dose. Signs of heat will subside within about 5 days and the dog will not ovulate. With either regimen, return to estrus varies from 1 to 9 months (average is 4 to 6 months). If the bitch returns to estrus less than 1 month after therapy is concluded, she should not be bred on that cycle. The manufacturer recommends that Ovaban not be used to suppress a bitch’s first estrus or to suppress more than two heat periods in a row. The drug should not be given to a bitch with a history of progesterone-dependent disease, such as mammary neoplasia or pyometra. Care should be used in administering the drug to older bitches that may already have some uterine changes and may be predisposed to pyometra with progesterone administration (see Chapter 16). The drug must not be administered to pregnant bitches because
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it can cause birth defects in offspring. Short-term side effects of progestogen administration include increased appetite, weight gain, lethargy, and possible mammary development. Injectable forms of progesterone are available for use as long-acting estrussuppressing agents. These drugs are used routinely in other countries. Examples include medroxyprogesterone acetate and proligestone. Side effects are as described for megestrol acetate. B.
ANDROGENS The only approved androgen for estrus suppression in bitches, mibolerone (Cheque drops), is not commercially available at this time and never was approved for use in breeding bitches. This drug must be administered in anestrus, with therapy beginning at least 30 days before proestrus onset. Dose is dependent on weight, with the exception of treatment of German shepherd dogs, which require a high dose no matter what their body weight. The drug is administered once daily by mouth for as long as estrus suppression is desired. Return to estrus after the drug is withdrawn varies from 7 days to 6.5 months, with an average return to estrus of 70 days. The drug should not be used to suppress a bitch’s first estrus and cannot be used in bitches with kidney or liver disease. Mibolerone must not be administered to pregnant bitches because it can cause birth defects in offspring. Short-term side effects include musky body odor, obesity, vaginitis and creamy white vulvar discharge, hypertrophy (enlargement) of the clitoris, and increased mounting and aggressive behaviors. Testosterone is used as an estrus-suppressing agent in racing greyhounds. Side effects are as described for mibolerone.
II.
STERILIZATION
A.
OVARIOHYSTERECTOMY OHE, or spay, is the complete removal of both ovaries, the uterine tubes, and the entire uterus, ideally to the level of the cervix (Figure 11-1). After OHE, bitches will not cycle, cannot get diseases of the reproductive tract, and are at decreased risk of developing mammary neoplasia. Bitches do not show a change in temperament after OHE any more than they show a change in temperament after breeding and whelping. In the United States, OHE is the most common veterinary surgery performed. Complications are uncommon but may occur. Fairly common shortterm complications that may be seen include bleeding from the sites where the ovaries or uterus were removed, opening of the incision, and infection of the incision. If the dog has internal bleeding after surgery, she recovers from anesthesia slowly and her mucous membranes are pale. Usually this occurs while she is still recovering in the hospital, and the veterinarian can quickly explore the abdomen and repair the bleeding site. Opening of the incision (dehiscence) occurs more commonly in very active dogs or in dogs that lick at the incision
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Figure 11-1. Ovariohysterectomy.
Figure 11-2. Obese bitch post-ovariohysterectomy.
excessively. This usually is easily repaired and the dog is sent home with an Elizabethan collar that prohibits her access to the incision area. Infection of the incision may occur in dogs that lick at the incision excessively; antibiotics can be dispensed by your veterinarian. Fairly common long-term sequelae to OHE include obesity and estrogenresponsive urinary incontinence (Figure 11-2). Obesity is the most common nutritional disorder in dogs, and many factors contribute to its development. Obesity should not develop after OHE in female dogs that are fed and exercised properly. Estrogen-responsive urinary incontinence may develop in bitches spayed at any age. Some reports suggest onset of urinary incontinence earlier in the dog’s
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life if she is spayed before 3 months of age. Estrogen-responsive urinary incontinence is more common in bitches weighing more than 20 kg (44 pounds) as adults. Exact pathogenesis is unknown. Bitches present for “leaking” of urine when relaxed; usually the owner reports finding urine spotting where the dog sleeps. Treatment with estrogen, usually in the form of oral diethylstilbestrol (DES) or phenylpropanolamine, both of which act to improve the closure of sphincters in the urinary tract, is usually effective. B.
OVARIECTOMY Ovariectomy is removal of the ovaries only. The uterus is left in place. Proponents of this surgery claim shorter surgery time, the presence of a smaller abdominal incision, and less abdominal trauma. Uterine disease should not occur in bitches that have undergone ovariectomy because any hormonal stimulus to the uterus was removed with the ovaries. Studies done to date have shown no difference in the frequency of short-term or long-term complications in dogs undergoing ovariectomy compared with dogs undergoing OHE. However, OHE still is the accepted standard of care for sterilization of female dogs in the United States.
C.
MISCELLANEOUS 1. Tubal Ligation Tying off or removal of a piece of both uterine tubes is a form of sterilization that is performed in humans. This method rarely is used in dogs. The bitch is infertile but still shows the physical and behavioral changes of estrus and is predisposed to uterine disease and mammary neoplasia as she ages. 2. Immunosterilization The technique of immunologic contraception involves vaccination of an animal against a protein in its own body, with subsequent development of antibodies and destruction of that protein. Attempts have been made to immunize animals against their own ova by injecting them with the zona pellucida from pigs. The zona pellucida is the outer covering of the egg. If antibodies bind to the zona pellucida, fertilization cannot occur. In some species, injection of zona pellucida proteins in very young animals has induced destruction of much of the functional ovarian tissue. Studies done in dogs have demonstrated abnormal estrus cycles in the treated bitches and need for frequent revaccination. This technique still is experimental at this time.
III.
PREGNANCY TERMINATION Bitches are presented for pregnancy termination when bred to an undesirable male of their own or another breed or when bred when too young or too old. The likelihood that the bitch is pregnant is the first question.
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How long ago was the bitch mismated?
Less than 7 days
More than 7 days
- The only drug that is effective in very early gestation for pregnancy termination in dogs is estrogen. Estrogen must be given while the dog is still in estrus and after she has ovulated; you must see your veterinarian for vaginal cytology (100% cornified with greater than 50% of the cells appearing to have no nucleus) and progesterone assay (greater than 4 ng/mL indicative of ovulation). - Because many dogs that were bred do not become pregnant and because estrogen can have significant side-effects, the author recommends all bitches be evaluated for pregnancy 30 days after the appropriate breeding and treated at midgestation if necessary.
- It is virtually impossible to retrospectively determine likelihood of the dog having been impregnated. The author strongly recommends the bitch be checked for pregnancy 30 days after the inappropriate breeding and the bitch treated at midgestation if necessary.
Figure 11-3. Pregnancy termination algorithm.
Vaginal cytology and measurement of progesterone in blood can be used to identify where she is in the estrous cycle and likelihood of conception. Remember that spermatozoa can easily live for a week in the bitch’s reproductive tract, so bitches bred early still may conceive. Examination of a vaginal swab for the presence of spermatozoa is unreliable in determining whether or not a given bitch was bred; if spermatozoa are seen, you know for sure breeding occurred, but if spermatozoa are not seen that does not mean breeding did not occur. Ideally bitches should be diagnosed pregnant before any therapy is administered. Studies have demonstrated that 30% to 38% of bitches presented for pregnancy termination are not in fact pregnant. Obviously, if this is a valuable breeding bitch, it is desirable not to treat unless absolutely necessary. Methods for pregnancy termination are described in Table 11-1. With any pregnancy termination technique, pups will be resorbed if pregnancy is terminated before about day 40. Fluid and tissues will be passed from days 40 to 50, and recognizable pups may be born alive after day 50. No published medical therapy is reported to be 100% effective. I prefer to offer OHE as the first option. If the bitch cannot be spayed, the author sees her about 30 days after the inappropriate mating to diagnose pregnancy before any therapy is administered (Figure 11-3).
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Table 11-1 Methods of Pregnancy Termination in Dogs Method
Specific Drug(s) Used
Mode of Action
Ovariohysterectomy
—
Physical removal of pregnancy
Estrogen
Estradiol cypionate (injectable; oral forms of estrogen do not work)
Slows egg as it moves into the uterine tube, preventing conception
Prostaglandin
Prostaglandin F2␣ Cloprostenol
Decreases progesterone concentration in blood, causes uterine contractions
Progesterone receptor blockers
Mifepristone (RU486) Aglepristone (not available in the United States)
Prolactin inhibitors
Bromocriptine Cabergoline
Glucocorticoids (steroids)
Dexamethasone
Block progesterone receptors; the body perceives this as a decline in progesterone concentration Prolactin secretion is necessary for continuing of the luteal tissue on ovary Decrease progesterone secretion through undefined mechanism
NOTE: Drugs may be used in combination; this may minimize side effects.
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Time After Breeding When Used Any time after breeding; surgery more difficult while bitch still in estrus and after midgestation. Must be administered after bitch has ovulated (progesterone concentration greater than 4 ng/mL) but before the bitch has gone into diestrus (noncornified vaginal cytology) Must be administered after the 5th day of diestrus; effective after that throughout gestation
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Pros
Cons
100% effective Prevents future reproductive tract disease and decreases predisposition to mammary neoplasia. Inexpensive Effective if given at correct stage of cycle
Irreversible Costly
Can be used after pregnancy diagnosis performed No apparent effect on future fertility
Side effects: vomiting, salivation, defecation (for about 30 min after drug injected) Multiple doses required, may require hospitalization Bitch may return to estrus earlier than expected Not readily available
May induce pyometra, ovarian cystic disease, decrease in platelet and red blood cell numbers (often life threatening) Prolongs standing heat
Midgestation
Effective with few side effects
Midgestation
Effective Often used in combination with prostaglandin
May cause vomiting (bromocriptine)
Midgestation
Can be given orally
80% effective Side effects: increased thirst and urination
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TEST YOUR UNDERSTANDING 1) Your son is showing your 9-year-old Shetland sheepdog as a junior handler in a regional show in 2 months. The dog has been cycling irregularly for the last 1 to 2 years. Your son does not want to spend his money on an entry fee that will be wasted if she goes into heat and asks you to call the veterinarian to get information about suppressing the bitch’s heat until after the show. Your vet informs you that the only drug available at this time is Ovaban. What are the pros and cons of this drug? Is your dog a good candidate? Pros: • If used as the manufacturer recommends, the reported incidence of uterine disease is less than 1%. • The drug can be given at the anestrus dose now and the dose increased if she enters proestrus unexpectedly. Con: • Possible side effects include mammary neoplasia, weight gain, lethargy, and diabetes mellitus. This is an older bitch with irregular cycles. She may already have some degree of change in her uterine lining (cystic endometrial hyperplasia; see Chapter 16) that may be worsened by exposure to this drug, which is a form of progesterone. 2) Your 1-year-old bitch is left outside unattended by the babysitter. The bitch is in heat for the first time and has been in heat for about 2 weeks. When you get home, you find her in the backyard with the neighbor’s intact male mixed-breed dog; they appear to be tied. When you shout at them, the male pulls away and runs. How likely is it that she will conceive? What are your options for pregnancy termination? Without vaginal cytology and progesterone measurement to determine timing of this breeding relative to ovulation, it is difficult to state the likelihood of her conceiving. However, if she is an average bitch, she ovulated on about day 11 of her season and had viable eggs when she was bred. Whether or not the dogs actually achieved a tie is of no concern; the tie is not necessary for pregnancy to be achieved. The first option for pregnancy termination is OHE, which can be performed anytime your veterinarian is comfortable doing it; most prefer to wait until the bitch has entered diestrus. If spaying is not an option, pregnancy can be diagnosed definitively in 30 days and treatment can be begun at that time. Another alternative would be to let her have the pups and to place them as pets. Possible disadvantages of this final choice are (1) the world does not need more mixed-breed pups, and (2) the single breeding may not have been near optimal breeding day, yielding a small litter and subsequently larger pups. Coupled with the young age of this bitch, dystocia (difficulty whelping) may be more likely.
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Bibliography Arnold S, Arnold P, Hubler M, et al: Urinary incontinence in spayed bitches: prevalence and breed predisposition. Schweiz Arch Tierheilk 131:259-263, 1989. Arnold S, Hubler M, Casal M, et al: The transplantation of autologous ovarian tissue in the bitch for the prevention of side effects due to spaying: a retrospective study several years after surgery. Eur Comp Anim Pract 3:67-71, 1992. Bowen RA, Olson PN, Behrendt MD, et al: Efficacy and toxicity of estrogens commonly used to terminate canine pregnancy. J Am Vet Med Assoc 186:783-788, 1985. Concannon PW, McCann JP, Temple M: Biology and endocrinology of ovulation, pregnancy and parturition in the dog. J Reprod Fertil Suppl 39:3-25, 1989. Concannon PW, Meyer-Wallen VN: Current and proposed methods for contraception and termination of pregnancy in dogs and cats. J Am Vet Med Assoc 198:1214-1225, 1991. Concannon PW, Yeager A, Frank D, et al: Termination of pregnancy and induction of premature luteolysis by an antiprogestogen, mifepristone, in dogs. J Reprod Fertil 88:99-104, 1990. Feldman EC, Davidson AP, Nelson RW, et al: Prostaglandin induction of abortion in pregnant bitches after misalliance. J Am Vet Med Assoc 202:1855-1858, 1993. Fieni F, Fuhrer M, Tainturier D, et al. Use of cloprostenol for pregnancy termination in dogs. J Reprod Fertil Suppl 39:332-333, 1989 (abstract). Galac S, Kooistra HS, Butinar J, et al: Termination of mid-gestation pregnancy in bitches with aglepristone, a progesterone receptor antagonist. Theriogenology 53:941-950, 2000. Gobello C, Castex G, Corrada Y, et al: Use of prostaglandins and bromocriptine mesylate for pregnancy termination in bitches. J Am Vet Med Assoc 220:1017-1019, 2002. Gonzalez A, Allen AF, Post K, et al: Immunological approaches to contraception in dogs. J Reprod Fertil 39:189-198, 1989. Houpt KA, Coren B, Hintz HF, et al: Effect of sex and reproductive status on sucrose preference, food intake and body weight of dogs. J Am Vet Med Assoc 174:10831085, 1979. Janssens LAA, Janssens GHRR: Bilateral flank ovariectomy in the dog: surgical technique and sequelae in 72 animals. J Small Anim Pract 32:249-252, 1991. Jochle W, Arbeiter K, Post K, et al: Effects on pseudopregnancy, pregnancy and interoestrus interval of pharmacological suppression of prolactin secretion in female dogs and cats. J Rep Fertil Suppl 39:199-207, 1989.
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Johnston SD, Root Kustritz MV, Olson PN: Canine and feline theriogenology, Philadelphia, 2001, Saunders, pp 168-192. Kutzler MA: Contraception and pregnancy termination. In Root Kustritz MV, editor: Small animal theriogenology, St Louis, 2003, Butterworth-Heinemann, pp 125-164. Lein DH, Concannon PW, Hornbuckle WE, et al: Termination of pregnancy in bitches by administration of prostaglandin F2␣. J Reprod Fertil Suppl 39:231-240, 1989. O’Farrell V, Peachey E: Behavioural effects of ovariohysterectomy on bitches. J Small Anim Pract 31:595-598, 1990. Okkens AC, Kooistra HS, Nickel RF: Comparison of long-term effects of ovariectomy versus ovariohysterectomy in bitches. J Reprod Fertil Suppl 51:227-231, 1997. Olson PN, Johnston SD: New developments in small animal population control. J Am Vet Med Assoc 202:904-909, 1993. Olson PN, Johnston SD, Root MV, et al: Terminating pregnancy in dogs and cats. Anim Reprod Sci 28:399-406, 1992. Romagnoli SE, Camillo F, Cela M, et al: Clinical use of prostaglandin F2␣ to induce early abortion in bitches: serum progesterone, treatment outcome and interval to subsequent oestrus. J Reprod Fertil Suppl 47:425-431, 1993. Romagnoli SE, Camillo F, Novellini S, et al: Luteolytic effects of prostaglandin F2␣ on day 8 to 19 corpora lutea in the bitch. Theriogenology 45:397-403, 1996. Schneider R, Dorn CR, Taylor DON: Factors influencing canine mammary cancer development and post-surgical survival. J Natl Cancer Inst 43:1249-1261, 1969. Seigl VH, Bohm R, Ferguson J, et al: Laparoscopic ovariohysterectomy in a dog. Wien Tierarzt Mschr 81:149-152, 1994. Wanke M, Loza ME, Monachesi N, et al: Clinical use of dexamethasone for termination of unwanted pregnancy in dogs. J Reprod Fertil Suppl 51:233-238, 1997. Whitacre MD, Yates DJ, VanCamp SD, et al: Detection of intravaginal spermatozoa after natural mating in the bitch. Vet Clin Pathol 21:85-87, 1992. Zone M, Wanke M, Rebuelto M, et al: Termination of pregnancy in dogs by oral administration of dexamethasone. Theriogenology 43:487-494, 1995.
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2) I think my dog got bred by accident. Can you do a vaginal examination to determine whether sperm are present? If there are spermatozoa visible on a vaginal swab, you know she got bred; if no spermatozoa are visible, that does not mean she did not get bred, however. 3) My dog just got bred by accident. What do I do now? There is one drug for pregnancy termination that is given at the time the dog was bred (estrogen). This drug has reproductive side effects and is not my drug of choice. I prefer to wait to see whether the dog is pregnant first by checking her 30 days after the accidental breeding. If she is not pregnant, great! If she is, we safely can terminate the pregnancy at that time.
I.
ESTRUS SUPPRESSION Suppression of estrus or heat may be attempted when a bitch is to be shown in obedience, worked in the field with male dogs, or otherwise is at a point where the physical and behavioral changes of heat would be disadvantageous for her or other dogs. Estrus suppression does not allow one to put off heat for a specific period; for example, one cannot use estrus-suppressing drugs to make sure a dog will cycle in a specific month. Estrus-suppressing drugs should be administered only if the owner is sure the dog will be bred in the future. Sterilization by ovariohysterectomy (OHE) is the preferred technique for the vast majority of female dogs in the United States.
A.
PROGESTOGENS The only estrus-suppressing agent approved for use in breeding bitches in the United States is the progestogen megestrol acetate (Ovaban). The drug can be used either during anestrus or within the first 3 days of proestrus. If administered during anestrus, the drug is given at a low dose daily for 32 days. If given within the first 3 days of proestrus, the drug is administered for 8 days at a higher dose. Signs of heat will subside within about 5 days and the dog will not ovulate. With either regimen, return to estrus varies from 1 to 9 months (average is 4 to 6 months). If the bitch returns to estrus less than 1 month after therapy is concluded, she should not be bred on that cycle. The manufacturer recommends that Ovaban not be used to suppress a bitch’s first estrus or to suppress more than two heat periods in a row. The drug should not be given to a bitch with a history of progesterone-dependent disease, such as mammary neoplasia or pyometra. Care should be used in administering the drug to older bitches that may already have some uterine changes and may be predisposed to pyometra with progesterone administration (see Chapter 16). The drug must not be administered to pregnant bitches because
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it can cause birth defects in offspring. Short-term side effects of progestogen administration include increased appetite, weight gain, lethargy, and possible mammary development. Injectable forms of progesterone are available for use as long-acting estrussuppressing agents. These drugs are used routinely in other countries. Examples include medroxyprogesterone acetate and proligestone. Side effects are as described for megestrol acetate. B.
ANDROGENS The only approved androgen for estrus suppression in bitches, mibolerone (Cheque drops), is not commercially available at this time and never was approved for use in breeding bitches. This drug must be administered in anestrus, with therapy beginning at least 30 days before proestrus onset. Dose is dependent on weight, with the exception of treatment of German shepherd dogs, which require a high dose no matter what their body weight. The drug is administered once daily by mouth for as long as estrus suppression is desired. Return to estrus after the drug is withdrawn varies from 7 days to 6.5 months, with an average return to estrus of 70 days. The drug should not be used to suppress a bitch’s first estrus and cannot be used in bitches with kidney or liver disease. Mibolerone must not be administered to pregnant bitches because it can cause birth defects in offspring. Short-term side effects include musky body odor, obesity, vaginitis and creamy white vulvar discharge, hypertrophy (enlargement) of the clitoris, and increased mounting and aggressive behaviors. Testosterone is used as an estrus-suppressing agent in racing greyhounds. Side effects are as described for mibolerone.
II.
STERILIZATION
A.
OVARIOHYSTERECTOMY OHE, or spay, is the complete removal of both ovaries, the uterine tubes, and the entire uterus, ideally to the level of the cervix (Figure 11-1). After OHE, bitches will not cycle, cannot get diseases of the reproductive tract, and are at decreased risk of developing mammary neoplasia. Bitches do not show a change in temperament after OHE any more than they show a change in temperament after breeding and whelping. In the United States, OHE is the most common veterinary surgery performed. Complications are uncommon but may occur. Fairly common shortterm complications that may be seen include bleeding from the sites where the ovaries or uterus were removed, opening of the incision, and infection of the incision. If the dog has internal bleeding after surgery, she recovers from anesthesia slowly and her mucous membranes are pale. Usually this occurs while she is still recovering in the hospital, and the veterinarian can quickly explore the abdomen and repair the bleeding site. Opening of the incision (dehiscence) occurs more commonly in very active dogs or in dogs that lick at the incision
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Figure 11-1. Ovariohysterectomy.
Figure 11-2. Obese bitch post-ovariohysterectomy.
excessively. This usually is easily repaired and the dog is sent home with an Elizabethan collar that prohibits her access to the incision area. Infection of the incision may occur in dogs that lick at the incision excessively; antibiotics can be dispensed by your veterinarian. Fairly common long-term sequelae to OHE include obesity and estrogenresponsive urinary incontinence (Figure 11-2). Obesity is the most common nutritional disorder in dogs, and many factors contribute to its development. Obesity should not develop after OHE in female dogs that are fed and exercised properly. Estrogen-responsive urinary incontinence may develop in bitches spayed at any age. Some reports suggest onset of urinary incontinence earlier in the dog’s
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life if she is spayed before 3 months of age. Estrogen-responsive urinary incontinence is more common in bitches weighing more than 20 kg (44 pounds) as adults. Exact pathogenesis is unknown. Bitches present for “leaking” of urine when relaxed; usually the owner reports finding urine spotting where the dog sleeps. Treatment with estrogen, usually in the form of oral diethylstilbestrol (DES) or phenylpropanolamine, both of which act to improve the closure of sphincters in the urinary tract, is usually effective. B.
OVARIECTOMY Ovariectomy is removal of the ovaries only. The uterus is left in place. Proponents of this surgery claim shorter surgery time, the presence of a smaller abdominal incision, and less abdominal trauma. Uterine disease should not occur in bitches that have undergone ovariectomy because any hormonal stimulus to the uterus was removed with the ovaries. Studies done to date have shown no difference in the frequency of short-term or long-term complications in dogs undergoing ovariectomy compared with dogs undergoing OHE. However, OHE still is the accepted standard of care for sterilization of female dogs in the United States.
C.
MISCELLANEOUS 1. Tubal Ligation Tying off or removal of a piece of both uterine tubes is a form of sterilization that is performed in humans. This method rarely is used in dogs. The bitch is infertile but still shows the physical and behavioral changes of estrus and is predisposed to uterine disease and mammary neoplasia as she ages. 2. Immunosterilization The technique of immunologic contraception involves vaccination of an animal against a protein in its own body, with subsequent development of antibodies and destruction of that protein. Attempts have been made to immunize animals against their own ova by injecting them with the zona pellucida from pigs. The zona pellucida is the outer covering of the egg. If antibodies bind to the zona pellucida, fertilization cannot occur. In some species, injection of zona pellucida proteins in very young animals has induced destruction of much of the functional ovarian tissue. Studies done in dogs have demonstrated abnormal estrus cycles in the treated bitches and need for frequent revaccination. This technique still is experimental at this time.
III.
PREGNANCY TERMINATION Bitches are presented for pregnancy termination when bred to an undesirable male of their own or another breed or when bred when too young or too old. The likelihood that the bitch is pregnant is the first question.
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171
How long ago was the bitch mismated?
Less than 7 days
More than 7 days
- The only drug that is effective in very early gestation for pregnancy termination in dogs is estrogen. Estrogen must be given while the dog is still in estrus and after she has ovulated; you must see your veterinarian for vaginal cytology (100% cornified with greater than 50% of the cells appearing to have no nucleus) and progesterone assay (greater than 4 ng/mL indicative of ovulation). - Because many dogs that were bred do not become pregnant and because estrogen can have significant side-effects, the author recommends all bitches be evaluated for pregnancy 30 days after the appropriate breeding and treated at midgestation if necessary.
- It is virtually impossible to retrospectively determine likelihood of the dog having been impregnated. The author strongly recommends the bitch be checked for pregnancy 30 days after the inappropriate breeding and the bitch treated at midgestation if necessary.
Figure 11-3. Pregnancy termination algorithm.
Vaginal cytology and measurement of progesterone in blood can be used to identify where she is in the estrous cycle and likelihood of conception. Remember that spermatozoa can easily live for a week in the bitch’s reproductive tract, so bitches bred early still may conceive. Examination of a vaginal swab for the presence of spermatozoa is unreliable in determining whether or not a given bitch was bred; if spermatozoa are seen, you know for sure breeding occurred, but if spermatozoa are not seen that does not mean breeding did not occur. Ideally bitches should be diagnosed pregnant before any therapy is administered. Studies have demonstrated that 30% to 38% of bitches presented for pregnancy termination are not in fact pregnant. Obviously, if this is a valuable breeding bitch, it is desirable not to treat unless absolutely necessary. Methods for pregnancy termination are described in Table 11-1. With any pregnancy termination technique, pups will be resorbed if pregnancy is terminated before about day 40. Fluid and tissues will be passed from days 40 to 50, and recognizable pups may be born alive after day 50. No published medical therapy is reported to be 100% effective. I prefer to offer OHE as the first option. If the bitch cannot be spayed, the author sees her about 30 days after the inappropriate mating to diagnose pregnancy before any therapy is administered (Figure 11-3).
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Table 11-1 Methods of Pregnancy Termination in Dogs Method
Specific Drug(s) Used
Mode of Action
Ovariohysterectomy
—
Physical removal of pregnancy
Estrogen
Estradiol cypionate (injectable; oral forms of estrogen do not work)
Slows egg as it moves into the uterine tube, preventing conception
Prostaglandin
Prostaglandin F2␣ Cloprostenol
Decreases progesterone concentration in blood, causes uterine contractions
Progesterone receptor blockers
Mifepristone (RU486) Aglepristone (not available in the United States)
Prolactin inhibitors
Bromocriptine Cabergoline
Glucocorticoids (steroids)
Dexamethasone
Block progesterone receptors; the body perceives this as a decline in progesterone concentration Prolactin secretion is necessary for continuing of the luteal tissue on ovary Decrease progesterone secretion through undefined mechanism
NOTE: Drugs may be used in combination; this may minimize side effects.
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Time After Breeding When Used Any time after breeding; surgery more difficult while bitch still in estrus and after midgestation. Must be administered after bitch has ovulated (progesterone concentration greater than 4 ng/mL) but before the bitch has gone into diestrus (noncornified vaginal cytology) Must be administered after the 5th day of diestrus; effective after that throughout gestation
173
Pros
Cons
100% effective Prevents future reproductive tract disease and decreases predisposition to mammary neoplasia. Inexpensive Effective if given at correct stage of cycle
Irreversible Costly
Can be used after pregnancy diagnosis performed No apparent effect on future fertility
Side effects: vomiting, salivation, defecation (for about 30 min after drug injected) Multiple doses required, may require hospitalization Bitch may return to estrus earlier than expected Not readily available
May induce pyometra, ovarian cystic disease, decrease in platelet and red blood cell numbers (often life threatening) Prolongs standing heat
Midgestation
Effective with few side effects
Midgestation
Effective Often used in combination with prostaglandin
May cause vomiting (bromocriptine)
Midgestation
Can be given orally
80% effective Side effects: increased thirst and urination
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TEST YOUR UNDERSTANDING 1) Your son is showing your 9-year-old Shetland sheepdog as a junior handler in a regional show in 2 months. The dog has been cycling irregularly for the last 1 to 2 years. Your son does not want to spend his money on an entry fee that will be wasted if she goes into heat and asks you to call the veterinarian to get information about suppressing the bitch’s heat until after the show. Your vet informs you that the only drug available at this time is Ovaban. What are the pros and cons of this drug? Is your dog a good candidate? Pros: • If used as the manufacturer recommends, the reported incidence of uterine disease is less than 1%. • The drug can be given at the anestrus dose now and the dose increased if she enters proestrus unexpectedly. Con: • Possible side effects include mammary neoplasia, weight gain, lethargy, and diabetes mellitus. This is an older bitch with irregular cycles. She may already have some degree of change in her uterine lining (cystic endometrial hyperplasia; see Chapter 16) that may be worsened by exposure to this drug, which is a form of progesterone. 2) Your 1-year-old bitch is left outside unattended by the babysitter. The bitch is in heat for the first time and has been in heat for about 2 weeks. When you get home, you find her in the backyard with the neighbor’s intact male mixed-breed dog; they appear to be tied. When you shout at them, the male pulls away and runs. How likely is it that she will conceive? What are your options for pregnancy termination? Without vaginal cytology and progesterone measurement to determine timing of this breeding relative to ovulation, it is difficult to state the likelihood of her conceiving. However, if she is an average bitch, she ovulated on about day 11 of her season and had viable eggs when she was bred. Whether or not the dogs actually achieved a tie is of no concern; the tie is not necessary for pregnancy to be achieved. The first option for pregnancy termination is OHE, which can be performed anytime your veterinarian is comfortable doing it; most prefer to wait until the bitch has entered diestrus. If spaying is not an option, pregnancy can be diagnosed definitively in 30 days and treatment can be begun at that time. Another alternative would be to let her have the pups and to place them as pets. Possible disadvantages of this final choice are (1) the world does not need more mixed-breed pups, and (2) the single breeding may not have been near optimal breeding day, yielding a small litter and subsequently larger pups. Coupled with the young age of this bitch, dystocia (difficulty whelping) may be more likely.
Chapter 11
Estrus Suppression, Sterilization, and Pregnancy Termination
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