INDUCED PARTURATION AND TERMINATION OF PREGANANCY IN ANIMALS
The induction of parturition is a very useful tool for managing the time of calving. For both the natural and induced parturitions, the stages of labour, pelvic relaxation, calf viability, colostral transfer and milk production are similar in healthy animals, but the knowledge of proper breeding dates and high incidences of retention of the placenta are main constraints. The induction of parturition is indicated to save the viability of the fetus as well as that of the cow. Since the fetus gains about 0.5 kg/day during the last weeks of normal gestation, induction of parturition can be a useful tool to prevent dystocia from an oversized fetus. Induction of parturition is also beneficial when the gestation is prolonged which allows the cows extra time to resume reproductive cyclicity to breed again. Potentially, parturition induction can be used to schedule calving to occur during daylight hours on known dates, so that it can be managed by the adequate number of personnel.
Indications
- Advancing the time of calving to coincide with the availability of suitable pasture for enhancing milk production.
- · To ensure that the cow parturate at a pre-determined time when skilled personnel is available so that proper attention can be given to the cows. ·
- To reduce the birth weight of the calf so as to reduce the occurrence of dystocia by shortening the length of gestation.
- · Also indicated in diseased or injured cows for the treatment of cardiac failure, uterine hydropsy or other critical conditions to save the life of fetus and cow.
- · To prevent udder edema and distension that predisposes difficulty in milking which may lead to mastitis.
Various protocols of induction of parturition
A number of studies have been carried out for the induction of parturition using different types and combinations of hormonal treatments along with their efficacy and safety.
They are described below.
Short-acting corticosteroids
The most widely used corticosteroid for induction of parturition is Dexamethasone (20 to 30 mg) or Flumethasone (8 to 10 mg) given as a single intramuscular injection. The efficacy of induction of parturition is 80 – 90% when it is administered within 2 weeks of the normal term. The parturition commences within 24 to 72 hours of administration of an injection. The average duration is 48 hours. Retreatment is often recommended if the parturition does not commence within 72 hours of injection.
Long and intermediate-acting corticosteroids
Long-acting corticosteroids are used when the lactation is to be synchronized with the grazing season and the viability of the calf is not important. It includes Dexamethasone trimethyl acetate (20 mg) or Triamcinolone acetonide (4 to 8 mg) (medium acting). The single intramuscular injection is to be administered one month before the due date of calving. The calving occurs over 4 to 26 days of administration of the injection. The udders of the treated cows get engorged with milk about one week after injection. Milking can be done in these animals before parturition if the udder is already full to prevent the regression of secondary tissue. The occurrence of retained placenta is quite less (9-22%) compared to short-acting corticosteroids. However, the incidence of calf mortality is more (7% to 45%) due to premature placental separation and also the birth of the premature calf.
Prostaglandins
Prostaglandins give similar results to induction of parturition as short-acting corticosteroids with a range of 24 -72 hours (average of 45 hours)from treatment to calving. There is also a high chance of retained placenta and failure of induction when administered within 2 weeks of the normal term.
Prostaglandin and corticosteroid combination
Hormones generally used for induction of parturition initiate endocrine events that are triggered by fetal cortisol. Corticosteroids remove the placental source of progesterone by converting placental progesterone into estrogen. Failure to induce parturition may occur due to the non-removal of the ovarian source of progesterone. On the other hand, prostaglandins remove the ovarian source of progesterone. But they may fail in the induction of parturition due to remaining placental progesterone. So, a combination of two hormones can remove both the sources of progesterone and can efficiently induce parturition. A combination of both prostaglandin and dexamethasone induces parturition within 25 to 42 hours of treatment and the interval from injection to calving is also less variable.
Combination of long-acting corticosteroid, dexamethasone, and cloprostenol
This combination is used to induce calving during daylight and a low incidence of retention of the placenta. Long-acting corticosteroids lead to the lowest incidence of retained placenta but there is high variability in the interval from treatment to calving, whereas, dexamethasone and cloprostenol combination has the least variability in the interval from treatment to calving. So, the combination of long-acting corticosteroid, dexamethasone and cloprostenol induce parturition in daylight hours with a low incidence of retained placenta.
Summary of treatments for induction of parturition in cattle
For early induction (250-275 days of gestation):
Long-acting corticosteroid followed by short-acting corticosteroid or PGF2αafter 8 days if the calving has not occurred. The calving occurs after 48 hours of the last injection.
For late induction (after 275 days of gestation): PGF2α or short-acting corticosteroid.
Some disadvantages of induction of parturition
- It is not always effective.
- · The birth weight of the calf in induced parturition is lower than that of normal parturition.
- · High incidence of retention of fetal membranes when the short-acting corticosteroids are used.
- · Milk yield is initially affected.
- There is a delay in reaching peak lactation.
Induction of parturition plays an important role in managing to calve, synchronizing the calving with the availability of pasture to maximize the milk production, in reducing the chances of post-partum health problems of the cow. But the treatment protocols are also having some undesired consequences like retention of the placenta which is harmful to the reproductive health of the cow. So, an effective treatment regimen at the proper time of the gestation period may give a successful induction of parturition.
UNWANTED PREGNANCY
If you find that your bitch is pregnant or you suspect she is, and it wasn’t planned, you do have options. 1. Care for her appropriately and let her have the pups 2. Have her desexed (if the pregnancy isn’t to far advanced) 3. Have her aborted (again if the pregnancy isn’t to far advanced) The first step is to determine when the bitch was on heat and when she was or may have been mated if possible. Having this information is essential to planning the best options for your dog. Next step is to confirm that she is indeed pregnant. In reality, if these dates are unknown, determining how far pregnant your bitch is, is very difficult. The only options is having a very experienced clinician ultrasound her and measure the fetuses which can then give some idea as to the fetal age. Pregnancy less that three weeks is hard to confirm. A blood test which can be done in the clinic to detect RELAXIN hormone can confirm pregnancy from three weeks post mating but if a negative test result occurs, it is recommended to repeat the test a week later to confirm either way. Ultrasound is commonly used at four weeks to confirm pregnancy. X-ray is used late in pregnancy to count pups which can then be helpful when planning the delivery. X-ray can not be used earlier in pregnancy as the fetal bones have not ossified and will not show.
DESEXING
If you are interested in desexing your bitch, this can be done safely until five weeks post mating. After this stage, extra care is required to support her during the procedure. The anaesthetic risk will increase due to the time needed to complete the surgery and the degree of blood loss due to the much larger volume of circulating blood in the pregnant uterus. We are extremely reluctant to desex animals further developed than seven weeks pregnant. Bitches desexed whilst pregnant can still have mammary development initially and require considerable aftercare. Strict rest and confinement is essential for 10 days. The incision/wound must be cared for appropriately, kept clean and dry and your dog may be prescribed medication to have during her recovery period.
ABORTION
Pregnant dogs can be aborted using a product called ALIZIN. Whilst it is registered for use in dogs as far pregnant as 45 days post mating, it is recommended to use this product prior to day 35 post mating. At this time, it is 94% effective, the fetuses have not ossified (started to develop bones) and therefore they are absorbed by the body rather than being expelled. This means your bitch should show only a slight thick discharge from the vulva as the only sign of the drug working. Given this it may be hard for you to be sure it has worked so an ultrasound 7-10 days after the last injection to confirm the pregnancy has been terminated is recommended. If the pregnancy is closer to 45 days post mating, having an ultrasound done seven days after the last treatment to confirm termination is required as a third treatment may be required. Bitches treated later than 45 days (if errors where made in dates or dates of mating are unknown) may still abort pups, some of these may survive but many will not.
SIDE EFFECTS
At the time of injections, some dogs experience some pain whilst receiving the injection which passes very quickly. Others may develop an inflammatory reaction where the injections were given. The risk of this is decreased by giving a maximum of 5ml per site. All inflammatory responses will recover with appropriate medical support within 28 days. Other side effects reported but not commonly seen at our clinic include:
• anorexia (not eating)
• excitement
• depression
• vomiting
• diarrhoea
Of key importance however is the following side effect – uterine infection (pyometra). Whilst reports suggest this only occurs in 3% of cases, this condition is potentially fatal and needs to be watched for.
Bitches suffering from this condition may show a variety of signs including:
• increased drinking • decreased appetite • weight gain/distended pendulous abdomen • vulval discharge • vomiting • overgrooming/licking her back end • lethargy If you note any of the above signs we strongly recommend seeking veterinary attention as soon as possible. Aborted bitches are also likely to have a shortened inter-estrous period. This means they are likely to come into season earlier. If this period is less that 4 months, decreased fertility at the next heat is possible. Some aborted bitches may also experience a phantom pregnancy after treatment. This means she may still “behave” pregnant for a period of time. This again is another reason to confirm the treatment worked by ultrasound.
When can you test for pregnancy?
There are several different tests available for pregnancy in bitches:
(1) Abdominal palpation
In this test, the vet will carefully feel the abdomen and try to locate the bulges in the uterus that contain the developing puppies. This is most reliable between 4 and 5 weeks after the mating, but is very tricky in larger bitches and any who are overweight. Nowadays, we wouldn’t routinely recommend this method, because it’s not terribly reliable – it’s very easy to miss a small puppy, or find a big lump of faeces and think it is a pup!
(2) Relaxin Blood Test
This is a blood test for the hormone relaxin which is produced by the developing placenta. It is a pretty reliable way to determine whether the bitch is genuinely pregnant, or just has a false pregnancy. In some pregnant bitches, the test will give a positive result at 22 days after mating – however, a negative result this early may simply mean the puppies aren’t developed enough yet, so it should be repeated 10-14 days later. It also doesn’t tell you whether the puppies are alive or not.
(3) Ultrasound scan
This is the method we prefer to use – it is accurate from about 3 ½ weeks after mating, and can tell you how healthy the puppies are. It cannot, however, tell you how many there are – you’ll need to wait until the puppies’ skeletons form (in the last 3 weeks) and then get an X-ray to count noses to know that.
Solution 1…
Spay her. If you don’t intend to breed from your bitch again, your vets can spay her even if she is in pup – although it is a more difficult and risky procedure, because the blood supply to the uterus is much bigger. It is not something we would routinely recommend, but there may be some situations when it is appropriate.
Solution 2…
Use medical treatment to cause her to reabsorb or abort the litter. This is usually the treatment of choice. Vets generally use a drug called aglepristone, which blocks the action of progesterone (the “pregnancy hormone”), causing the bitch to reabsorb the embryos (if given early enough in pregnancy). It takes the form of two injections 24 hours apart, given any time from 10 to 45 days after mating, and is effective in over 90% of cases. Occasionally, one or two of the puppies survive, so it is always useful to get a scan done 10 days afterwards, just to make sure.
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development)
Image-Courtesy-Google
Reference-On Request.
