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Contraception in the dog and cat
Br. vet. J. (1984) . 140, 1 3 2
CONTRACEPTION IN THE DOG AND CAT E . K . M . JACKSON Stagenhoe Quarantine Cattery, St Paul's Walden, Hitchen, Herts
Contraception, the prevention of pregnancy, can be achieved by any method which prevents the union of sperm and follicle . In the case of the dog and cat contraception is seldom necessary for the animals' well-being, but is sought for the owner's convenience, and it therefore behoves the veterinary surgeon to discuss fully the various options . Notwithstanding this, it is essential from the social angle to limit the production of unwanted kittens and puppies . Contraception may be achieved by confinement or by surgical or chemical methods . Whereas formerly confinement was the method of choice, followed closely by surgery, various chemical methods are now in vogue, and it is not always realized, even by veterinary surgeons, that the way these chemicals work is not fully understood, and that for this reason alone they are inherently dangerous . All methods are associated with some danger but whereas in the case of confinement or surgery the dangers are most likely to be immediate, adverse results from the use of chemical contraceptives may not appear for many years .
CONTRACEPTION IN THE BITCH
Confinement Confinement is still the method most commonly used in country districts where the bitch is simply shut away in a stable for the full three weeks or sent to a suitable boarding kennels . Less knowledgeable owners should be warned that although mating usually occurs about 10 to 12 days after blood-show, pheramones in the urine are attractive to the male dog from day 1, and that therefore it is necessary to confine the bitch for the full three weeks to avoid being pestered by canine suitors . They should also be warned that some bitches have so much sex drive that they will chew through wooden doors or jump through glass windows in their efforts to find a mate and, when this is coupled with a dog's equal determination to reach the bitch, `confinement' may not be achieved . Urban restriction along with the high cost of good kenneling often drives owners to their veterinary surgeon for advice on other methods .
Surgical methods Surgical methods in the bitch include ovariectomy and tubal ligation but by far the most common method is ovarohysterectomy as by its very nature it excludes the risk of later uterine disorders . Ovarohysterectomy may lead to a small increase in weight, particularly in breeds prone to weight problems such as labradors and cocker spaniels . It may
CONTRACEPTION IN THE DOG AND CAT
133
also cause deterioration in the quality of the coat particularly in the silky-coated breeds such as setters . There is considerable controversy regarding the optimum age for spaying and, leaving aside the anthropomorphic ideas of the owner who feels that it would be `kinder' to allow the bitch one litter, even veterinary surgeons' opinions differ . In the USA the `stab' method performed at 3 . 5 months old was at one time popular, but it is now recognized that this may lead to urinary incontinence and a juvenile vulva . In much of Europe veterinary surgeons prefer to spay after the first season, which it must be remembered can occur any time between the age of three months and well over one year . In the UK many veterinary surgeons advocate five to six months, the time being based on inoculation status, anaesthetic risk, size and handleability more than on sexual development, but there are some who agree with their European colleagues . It is generally agreed that the operation is more difficult (and therefore more risky) when performed on a bitch in pro-oestrus or oestrus, due to the increased vascularity and friability of the uterus . Mature, and more particularly aged, bitches should be spayed during anoestrus, and for those that have recently whelped the delay should be at least six weeks . The site of the operation appears to vary with the veterinary school at which the surgeon trained, and although the author favours the flank approach, others use a paramedian or mid-line incision with equal success .
Chemical methods Chemical contraceptives are used in one of three ways : 1 . To prevent the onset of oestrus, when the chemical agent is given to a bitch in anoestrus, and by subsequent administrations the prevention can be almost permanent . 2 . To delay the onset of oestrus, a use mainly confined to the canine `professionals', i .e . breeders and greyhound owners . 3 . To suppress signs of pro-oestrus or oestrus, where the chemical agent is given, again usually at the request of breeders wishing to show their bitches, after signs have appeared . Much research has been undertaken and there is no doubt that the products now available are much safer than those formerly recommended, but perusal of the 'contraindications and warning sections' of data sheets confirm that there is still some danger with regard to future breeding difficulties, and even some to general health . Perhaps the most alarming aspect is the differences between the information given on such data sheets on what is meant to be an identical product . One of the inherent difficulties is that pharmaceutical chemists appear to think that bitches come into season every six months, whereas it is well known that there are `eight month' bitches and `10 month' bitches, and bitches that are immediately brought into season by another in the same state . Hitherto testosterone implants and androgenic anabolic steroids have been tried, but the group of drugs now commonly used are progestagens . The latest, proligestone (14a17a-propylidenedioxy progesterone) (Delvosteron, Mycofarm plc) is claimed to be safe to use for prevention, delay or suppression of oestrus . Other progestagens in common use are megestrol acetate (Ovarid, Glaxo) and medroxyprogesterone acetate (Anoestrulin, Berk ; Perlutex, Leo ; Promone E, Upjohn) . In every case the dose regime is complicated and is usually on a weight basis . Proligestone is administered by subcutaneous injection, whereas megestrol acetate is in tablet form, and medroxyprogesterone acetate can be
1 34
BRITISH VETERINARY JOURNAL, 140, 2
given by either route . The pros and cons of injections entailing visits to the surgery and tablets administered (or forgotten) by the owner, are amongst the considerations to be discussed with an owner . Prevention of implantation of the ovum Although this is not strictly contraception, the treatment of misalliance should perhaps be included . The group of drugs used are those with oestrogenic properties which bring the bitch back into season . It is in no way a safe procedure, frequently leading to a prolonged `second' season, and, in some cases, to pyometra or infertility . With rare exceptions it is better for the bitch to let her have the pups . The two most common drugs used are : 1 . Stilboestrol tablets . (The injection is no longer available .) Commencing on the 14th day after misalliance, an oral dose of 5 mg/day for 21 days or until blood-show . 2 . Oestradiol benzoate (Intervet) . An injection of 5 to 10 mg once only, within four days of mating .
THE MALE DOG Castration of the dog is a simple surgical procedure . It is frowned upon by the majority of the dog-owning public, presumably because they hold in their minds' eye the image of the eunuch, the bullock, the wether or other castrate . They feel, and perhaps with some justification, that a dog is not a dog unless he is a bit of a libertine . Certainly many castrates do put on weight, and some develop skin problems, but the change in their nature is not necessarily as great as is feared . Vasectomy, now more acceptable in the human world, might become more popular with dog owners in the future, but at present the few owners who ask for their dogs' castration do so for behavioural problems rather than as a means of contraception .
CONTRACEPTION IN THE QUEEN The queen, as all cat-lovers know, should never be considered as just a small bitch, and nowhere is this more evident than in her sex life . A `normal' queen will have an annual breeding season of 10 to 12 months, during which time she will, unless mated, come into season every three weeks . It should be added that few cats are `normal' . Almost any stress, environmental, climatic or social, can, and frequently does, interrupt the `normal' pattern, making it particularly difficult to predict a result, or even to know whether the result is due to a contraceptive procedure or to the queen's own `abnormal' hormonal activity . For these reasons, even though the three methods of confinement, surgery and the administration of chemical agents are discussed below, surgery is the method of choice in the great majority of cases . Confinement Many cat owners, particularly those who want one litter of kittens, initially try to confine their cats, and in some cases, where for instance they live in a flat and the cat has
CONTRACEPTION IN THE DOG AND CAT
1 35
never been outside, they may be successful . With others the attempt is short-lived as they are deafened by the sheer noise emanating from their beloved cat, this being particularly the case with the exotic breeds . In general, confinement is only advocated for those breeders who regularly keep their cats confined in purpose-built comfortable houses .
Surgical methods Ovariectomy and tubal ligation are both effective but complete ovarohysterectomy is advocated to avoid the possibility of later uterine disorders . It must be complete, for there are records of post-spaying oestrus and even abdominal pregnancy when portions of an ovary have been left in situ, and of pyometra if any uterine tissue is left . The optimum age is again debatable . Many veterinary surgeons like to spay young queens when they are between four and five months old, and certainly, so long as the kitten has confidence in the human race and does not struggle during the anaesthetic procedure, this is the age at which the actual surgical procedure is most simple . Queens vary greatly as to when they have their first oestrus, the average being around seven months of age, with many shorthairs coming into season much earlier at around 3 . 5 months . The procedure is slightly more difficult if performed when the queen is in oestrus, but as many owners do not recognize the signs, the veterinary surgeon may well be faced with an unexpectedly vascular and friable uterus . The best approach is through a flank incision with the proviso that in pale-coated queens such as Siamese the new growth of hair in the shaven area may come through as a dark patch due to temperature stress, and cause owners considerable annoyance . In the majority of cases the hair returns to its normal colour after a full moult .
Chemical methods A great deal of work has been done under laboratory conditions on the action of various chemical agents both in relation to the induction of oestrus in infertile queens and to oestrus suppression . There are very few reports of work in the field, i .e . in the `normal' cat, and it is only recently that a few veterinary surgeons have started to use chemical contraceptives in felines . Although progestagens are the favoured group of chemicals it is recognized that their long-term use may cause endometrial changes, some of which are only transient, and also hyperplasia of the mammary glands . In a species which is prone to breeding problems-if you want them to breed they won't and vice versa-it may well be unwise to use chemical contraceptives in a queen from whom it is hoped to breed at a later date . Certainly it is unwise for a veterinary surgeon to give an injection of any progestagen and then tell the owner that its effect will last for x months-the cat will almost certainly prove him wrong . Proligestone (Delvosteron, Mycofarm plc) . The makers claim that proligestone can be used, usually in a dose of 1 ml subcutaneously, for suppression of oestrus for about 6 . 5 months, and that by using a regimen of injections at certain intervals this suppression can be maintained . Megestrol acetate (Ovarid, Glaxo) . This drug is probably more often used in the treatment of coat conditions than as a contraceptive . It has the advantage that being in tablet form the dose can be easily adjusted . If administration is started during dioestrus a dose of 2 . 5 mg/day will suppress oestrus and can be continued for a period of up to two months . This is probably the drug of choice if short-term suppression is required . If treat-
1 36
BRITISH VETERINARY JOURNAL, 140, 2
ment is started during anoestrus (a state into which not all cats enter), a dose of 2 . 5 mg once a week is sufficient, and this may be continued for a period of 18 months . Medroxyprogesterone acetate is not recommended in the cat .
THE TOM CAT Although the three methods of confinement, surgery and the administration of chemical contraceptives, are all possible, surgical castration is usually preferred . Unlike in the dog, it is rare to find a pet cat owner who does not wish to have his kitten castrated . They realize that the fully-grown entire male cat may be smelly, most probably will spray furniture etc, and will certainly fight in defence of his territory, necessitating frequent visits to the vet . for the treatment of abscesses and cellulitis . There are of course some who maintain that a torn must remain a tom, but they usually soon change their minds unless they are living deep in the country where the cat has few contenders in a large territory .
Confinement Confinement is used by many breeders who provide special housing for their stud toms . Such cats are unlikely to wander even when they are let out as they have a sufficiently large harem at close quarters . Unwittingly there is another section of the public who use this method, for the author has met fully-grown toms who, because they have been kept in a flat all their lives, totally isolated from other cats, have never developed any sexual desires and do not know that they are toms . It should perhaps be added that if released from this isolation they learn very quickly!
Surgical methods The controversy is not about whether to castrate but when . A tom reaches sexual maturity at any time between 3 . 5 months and about one year-the shorthairs earlier than the long-haired breeds, and there is some advantage in performing the operation before the habit of spraying etc . has been established . There are, however, many veterinary surgeons, again mainly in the USA and mainland Europe, who insist on waiting until after the cat is six months old . One author has suggested that there is a connection between early castration and feline urethritis syndrome (FUS), but this has been refuted by another . Certainly in the good old days when the routine was "roll the three-and-half month-old kitten in a sack on the kitchen table, whip! whip! and all over in 10 seconds flat" FUS was not a problem . As far as surgery is concerned 3 . 5 to 4 months is the optimum age, as ligation of the blood vessels is seldom necessary . However the handling of a nervous kitten of that age for the now obligatory anaesthetic procedure requires more skill than for the actual surgery, and, for this reason alone, many prefer an age of 4 . 5 to 6 months . At this age some form of haemostasis is necessary be it `tying a knot in itself or actual ligation of the spermatic artery . Castration of the adult male is preferably performed in mid winter when the tom is less likely to be sexually active, but in general practice this recommendation is usually ignored . However it is well known that the sexually-active male cat can bleed to death as the result of an insecure ligature .
CONTRACEPTION IN THE DOG AND CAT
1 37
Chemical contraceptives This is seldom if ever indicated in the male cat . It has been found that alfachlorohydrin affects the motility of the spermatozoa and results in sterility, but this is probably only of academic interest .
CONCLUSION It has been mentioned that some form of contraception is a social necessity to prevent the production of unwanted pups and kittens, and this highlights the variety of situations which have to be considered . The best method of preventing pregnancy in a feral cat colony is not necessarily the same as that for a pet dog, a show cat or a racing greyhound . Even when a decision has been reached, it may have to be modified because, for instance, it is found that a particular client is incapable of maintaining a dose regimen . It has been attempted here to give a general idea of the methods available ; it remains to individual veterinary surgeons to decide, in consultation with the owner, what is the best method in each case .
CONTRACEPTION IN THE DOG AND CAT E . K . M . JACKSON Stagenhoe Quarantine Cattery, St Paul's Walden, Hitchen, Herts
Contraception, the prevention of pregnancy, can be achieved by any method which prevents the union of sperm and follicle . In the case of the dog and cat contraception is seldom necessary for the animals' well-being, but is sought for the owner's convenience, and it therefore behoves the veterinary surgeon to discuss fully the various options . Notwithstanding this, it is essential from the social angle to limit the production of unwanted kittens and puppies . Contraception may be achieved by confinement or by surgical or chemical methods . Whereas formerly confinement was the method of choice, followed closely by surgery, various chemical methods are now in vogue, and it is not always realized, even by veterinary surgeons, that the way these chemicals work is not fully understood, and that for this reason alone they are inherently dangerous . All methods are associated with some danger but whereas in the case of confinement or surgery the dangers are most likely to be immediate, adverse results from the use of chemical contraceptives may not appear for many years .
CONTRACEPTION IN THE BITCH
Confinement Confinement is still the method most commonly used in country districts where the bitch is simply shut away in a stable for the full three weeks or sent to a suitable boarding kennels . Less knowledgeable owners should be warned that although mating usually occurs about 10 to 12 days after blood-show, pheramones in the urine are attractive to the male dog from day 1, and that therefore it is necessary to confine the bitch for the full three weeks to avoid being pestered by canine suitors . They should also be warned that some bitches have so much sex drive that they will chew through wooden doors or jump through glass windows in their efforts to find a mate and, when this is coupled with a dog's equal determination to reach the bitch, `confinement' may not be achieved . Urban restriction along with the high cost of good kenneling often drives owners to their veterinary surgeon for advice on other methods .
Surgical methods Surgical methods in the bitch include ovariectomy and tubal ligation but by far the most common method is ovarohysterectomy as by its very nature it excludes the risk of later uterine disorders . Ovarohysterectomy may lead to a small increase in weight, particularly in breeds prone to weight problems such as labradors and cocker spaniels . It may
CONTRACEPTION IN THE DOG AND CAT
133
also cause deterioration in the quality of the coat particularly in the silky-coated breeds such as setters . There is considerable controversy regarding the optimum age for spaying and, leaving aside the anthropomorphic ideas of the owner who feels that it would be `kinder' to allow the bitch one litter, even veterinary surgeons' opinions differ . In the USA the `stab' method performed at 3 . 5 months old was at one time popular, but it is now recognized that this may lead to urinary incontinence and a juvenile vulva . In much of Europe veterinary surgeons prefer to spay after the first season, which it must be remembered can occur any time between the age of three months and well over one year . In the UK many veterinary surgeons advocate five to six months, the time being based on inoculation status, anaesthetic risk, size and handleability more than on sexual development, but there are some who agree with their European colleagues . It is generally agreed that the operation is more difficult (and therefore more risky) when performed on a bitch in pro-oestrus or oestrus, due to the increased vascularity and friability of the uterus . Mature, and more particularly aged, bitches should be spayed during anoestrus, and for those that have recently whelped the delay should be at least six weeks . The site of the operation appears to vary with the veterinary school at which the surgeon trained, and although the author favours the flank approach, others use a paramedian or mid-line incision with equal success .
Chemical methods Chemical contraceptives are used in one of three ways : 1 . To prevent the onset of oestrus, when the chemical agent is given to a bitch in anoestrus, and by subsequent administrations the prevention can be almost permanent . 2 . To delay the onset of oestrus, a use mainly confined to the canine `professionals', i .e . breeders and greyhound owners . 3 . To suppress signs of pro-oestrus or oestrus, where the chemical agent is given, again usually at the request of breeders wishing to show their bitches, after signs have appeared . Much research has been undertaken and there is no doubt that the products now available are much safer than those formerly recommended, but perusal of the 'contraindications and warning sections' of data sheets confirm that there is still some danger with regard to future breeding difficulties, and even some to general health . Perhaps the most alarming aspect is the differences between the information given on such data sheets on what is meant to be an identical product . One of the inherent difficulties is that pharmaceutical chemists appear to think that bitches come into season every six months, whereas it is well known that there are `eight month' bitches and `10 month' bitches, and bitches that are immediately brought into season by another in the same state . Hitherto testosterone implants and androgenic anabolic steroids have been tried, but the group of drugs now commonly used are progestagens . The latest, proligestone (14a17a-propylidenedioxy progesterone) (Delvosteron, Mycofarm plc) is claimed to be safe to use for prevention, delay or suppression of oestrus . Other progestagens in common use are megestrol acetate (Ovarid, Glaxo) and medroxyprogesterone acetate (Anoestrulin, Berk ; Perlutex, Leo ; Promone E, Upjohn) . In every case the dose regime is complicated and is usually on a weight basis . Proligestone is administered by subcutaneous injection, whereas megestrol acetate is in tablet form, and medroxyprogesterone acetate can be
1 34
BRITISH VETERINARY JOURNAL, 140, 2
given by either route . The pros and cons of injections entailing visits to the surgery and tablets administered (or forgotten) by the owner, are amongst the considerations to be discussed with an owner . Prevention of implantation of the ovum Although this is not strictly contraception, the treatment of misalliance should perhaps be included . The group of drugs used are those with oestrogenic properties which bring the bitch back into season . It is in no way a safe procedure, frequently leading to a prolonged `second' season, and, in some cases, to pyometra or infertility . With rare exceptions it is better for the bitch to let her have the pups . The two most common drugs used are : 1 . Stilboestrol tablets . (The injection is no longer available .) Commencing on the 14th day after misalliance, an oral dose of 5 mg/day for 21 days or until blood-show . 2 . Oestradiol benzoate (Intervet) . An injection of 5 to 10 mg once only, within four days of mating .
THE MALE DOG Castration of the dog is a simple surgical procedure . It is frowned upon by the majority of the dog-owning public, presumably because they hold in their minds' eye the image of the eunuch, the bullock, the wether or other castrate . They feel, and perhaps with some justification, that a dog is not a dog unless he is a bit of a libertine . Certainly many castrates do put on weight, and some develop skin problems, but the change in their nature is not necessarily as great as is feared . Vasectomy, now more acceptable in the human world, might become more popular with dog owners in the future, but at present the few owners who ask for their dogs' castration do so for behavioural problems rather than as a means of contraception .
CONTRACEPTION IN THE QUEEN The queen, as all cat-lovers know, should never be considered as just a small bitch, and nowhere is this more evident than in her sex life . A `normal' queen will have an annual breeding season of 10 to 12 months, during which time she will, unless mated, come into season every three weeks . It should be added that few cats are `normal' . Almost any stress, environmental, climatic or social, can, and frequently does, interrupt the `normal' pattern, making it particularly difficult to predict a result, or even to know whether the result is due to a contraceptive procedure or to the queen's own `abnormal' hormonal activity . For these reasons, even though the three methods of confinement, surgery and the administration of chemical agents are discussed below, surgery is the method of choice in the great majority of cases . Confinement Many cat owners, particularly those who want one litter of kittens, initially try to confine their cats, and in some cases, where for instance they live in a flat and the cat has
CONTRACEPTION IN THE DOG AND CAT
1 35
never been outside, they may be successful . With others the attempt is short-lived as they are deafened by the sheer noise emanating from their beloved cat, this being particularly the case with the exotic breeds . In general, confinement is only advocated for those breeders who regularly keep their cats confined in purpose-built comfortable houses .
Surgical methods Ovariectomy and tubal ligation are both effective but complete ovarohysterectomy is advocated to avoid the possibility of later uterine disorders . It must be complete, for there are records of post-spaying oestrus and even abdominal pregnancy when portions of an ovary have been left in situ, and of pyometra if any uterine tissue is left . The optimum age is again debatable . Many veterinary surgeons like to spay young queens when they are between four and five months old, and certainly, so long as the kitten has confidence in the human race and does not struggle during the anaesthetic procedure, this is the age at which the actual surgical procedure is most simple . Queens vary greatly as to when they have their first oestrus, the average being around seven months of age, with many shorthairs coming into season much earlier at around 3 . 5 months . The procedure is slightly more difficult if performed when the queen is in oestrus, but as many owners do not recognize the signs, the veterinary surgeon may well be faced with an unexpectedly vascular and friable uterus . The best approach is through a flank incision with the proviso that in pale-coated queens such as Siamese the new growth of hair in the shaven area may come through as a dark patch due to temperature stress, and cause owners considerable annoyance . In the majority of cases the hair returns to its normal colour after a full moult .
Chemical methods A great deal of work has been done under laboratory conditions on the action of various chemical agents both in relation to the induction of oestrus in infertile queens and to oestrus suppression . There are very few reports of work in the field, i .e . in the `normal' cat, and it is only recently that a few veterinary surgeons have started to use chemical contraceptives in felines . Although progestagens are the favoured group of chemicals it is recognized that their long-term use may cause endometrial changes, some of which are only transient, and also hyperplasia of the mammary glands . In a species which is prone to breeding problems-if you want them to breed they won't and vice versa-it may well be unwise to use chemical contraceptives in a queen from whom it is hoped to breed at a later date . Certainly it is unwise for a veterinary surgeon to give an injection of any progestagen and then tell the owner that its effect will last for x months-the cat will almost certainly prove him wrong . Proligestone (Delvosteron, Mycofarm plc) . The makers claim that proligestone can be used, usually in a dose of 1 ml subcutaneously, for suppression of oestrus for about 6 . 5 months, and that by using a regimen of injections at certain intervals this suppression can be maintained . Megestrol acetate (Ovarid, Glaxo) . This drug is probably more often used in the treatment of coat conditions than as a contraceptive . It has the advantage that being in tablet form the dose can be easily adjusted . If administration is started during dioestrus a dose of 2 . 5 mg/day will suppress oestrus and can be continued for a period of up to two months . This is probably the drug of choice if short-term suppression is required . If treat-
1 36
BRITISH VETERINARY JOURNAL, 140, 2
ment is started during anoestrus (a state into which not all cats enter), a dose of 2 . 5 mg once a week is sufficient, and this may be continued for a period of 18 months . Medroxyprogesterone acetate is not recommended in the cat .
THE TOM CAT Although the three methods of confinement, surgery and the administration of chemical contraceptives, are all possible, surgical castration is usually preferred . Unlike in the dog, it is rare to find a pet cat owner who does not wish to have his kitten castrated . They realize that the fully-grown entire male cat may be smelly, most probably will spray furniture etc, and will certainly fight in defence of his territory, necessitating frequent visits to the vet . for the treatment of abscesses and cellulitis . There are of course some who maintain that a torn must remain a tom, but they usually soon change their minds unless they are living deep in the country where the cat has few contenders in a large territory .
Confinement Confinement is used by many breeders who provide special housing for their stud toms . Such cats are unlikely to wander even when they are let out as they have a sufficiently large harem at close quarters . Unwittingly there is another section of the public who use this method, for the author has met fully-grown toms who, because they have been kept in a flat all their lives, totally isolated from other cats, have never developed any sexual desires and do not know that they are toms . It should perhaps be added that if released from this isolation they learn very quickly!
Surgical methods The controversy is not about whether to castrate but when . A tom reaches sexual maturity at any time between 3 . 5 months and about one year-the shorthairs earlier than the long-haired breeds, and there is some advantage in performing the operation before the habit of spraying etc . has been established . There are, however, many veterinary surgeons, again mainly in the USA and mainland Europe, who insist on waiting until after the cat is six months old . One author has suggested that there is a connection between early castration and feline urethritis syndrome (FUS), but this has been refuted by another . Certainly in the good old days when the routine was "roll the three-and-half month-old kitten in a sack on the kitchen table, whip! whip! and all over in 10 seconds flat" FUS was not a problem . As far as surgery is concerned 3 . 5 to 4 months is the optimum age, as ligation of the blood vessels is seldom necessary . However the handling of a nervous kitten of that age for the now obligatory anaesthetic procedure requires more skill than for the actual surgery, and, for this reason alone, many prefer an age of 4 . 5 to 6 months . At this age some form of haemostasis is necessary be it `tying a knot in itself or actual ligation of the spermatic artery . Castration of the adult male is preferably performed in mid winter when the tom is less likely to be sexually active, but in general practice this recommendation is usually ignored . However it is well known that the sexually-active male cat can bleed to death as the result of an insecure ligature .
CONTRACEPTION IN THE DOG AND CAT
1 37
Chemical contraceptives This is seldom if ever indicated in the male cat . It has been found that alfachlorohydrin affects the motility of the spermatozoa and results in sterility, but this is probably only of academic interest .
CONCLUSION It has been mentioned that some form of contraception is a social necessity to prevent the production of unwanted pups and kittens, and this highlights the variety of situations which have to be considered . The best method of preventing pregnancy in a feral cat colony is not necessarily the same as that for a pet dog, a show cat or a racing greyhound . Even when a decision has been reached, it may have to be modified because, for instance, it is found that a particular client is incapable of maintaining a dose regimen . It has been attempted here to give a general idea of the methods available ; it remains to individual veterinary surgeons to decide, in consultation with the owner, what is the best method in each case .