| Management of the in-foal mare |
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Once the pregnant mare is back at home, she will still require: • Daily inspection • Regular hoof care • Appropriate feeding • Regular worming • Dental care • Vaccination. An influenza and tetanus booster 3-6 weeks before foaling gives the foal maximum protection. If the mare is to be vaccinated against Equine Herpes virus, this should be done in the 5th, 7th and 9th months of pregnancy. Vaccination of mares to protect their foals from diarrhoea caused by Equine Rotavirus is carried out in the 8th, 9th and 10th months of pregnancy • Exercise. This depends on many factors such as the size, age, condition and fitness of the mare and the weight of the rider. Strenuous exercise should be discontinued from the 6th month of gestation. The brood mare should be turned out each day. Pregnancy failure Failure to conceive and early embryonic loss This can be due to: • Genetic factors eg chromosomal abnormalities. Defects may occur if mating and fertilization does not take place at the optimum time and either the sperm or the egg are aged • Environmental factors. Malnutrition of the mare and over or underfeeding in the period after mating can adversely affect her fertility. Any illness resulting in a high temperature or prolonged colic can cause embryonic death • Uterine factors. Any problem with the previous pregnancy such as a difficult birth or retained placenta can adversely affect the uterine environment in a subsequent pregnancy. Pregnancies established at the foal heat have a reduced viability. The presence of endometrial cysts can sometimes affect embryonic development as can the presence of fluid retained in the uterus after mating. All mares experience a transient uterine inflammation after mating but this usually resolves within 48 hours. In older mares the inflammation may last for a longer time, and the embryo cannot survive under these conditions • Twin pregnancies Early embryonic loss may be predicted from the appearance on the ultrasound scan. The signs include: • An embryonic vesicle that is smaller than expected for its age • A vesicle with no embryo visible after the time when it should be seen • An embryo that is smaller than expected for its dates Twinning Nearly all twin pregnancies result from double ovulations. These may occur close together or several days apart within a single oestrous period. The incidence of double ovulations differs between breeds and increases with the age of the mare. Thoroughbred mares are reported to have a 15 – 25 % occurrence of double ovulations with a 15% incidence of twins. Twinning is a serious source of loss to the breeding industry. Various reports suggest that between 53 and 73% of affected mares will abort and of all the mares with twin pregnancies, only 16-25% of mares will give birth to single or twin foals. The cause of embryonic loss is the inability of the endometrium to provide adequate nutrition for both embryos. Twins located in the same horn are likely to die earlier in the pregnancy because the vesicles are in contact with each other rather than with the lining of the uterus and their nutrition is reduced. Diagnosis • In early pregnancy twinning is diagnosed by routine ultrasound examination per rectum • In late pregnancy, the presence of twins can sometimes be detected by scanning through the abdominal wall Subsequent action Following the diagnosis of a twin pregnancy, there are 3 possible courses of action: 1) Do nothing in the hope that one embryo will die naturally. The mare is checked at day 35 and if two foetuses are still present, she is injected with prostaglandins to abort the pregnancy 2) Try to eliminate one of the foetuses manually. If this is done before the embryos attach to the uterus (i.e. before about 16 days post ovulation), the success rate can be up to 90%. The smallest vesicle is gently manipulated until it reaches the tip of one uterine horn and compressed until it is felt to ‘pop’. If the foetuses are located in the same horn and have already become fixed to the endometrium, squeezing one is more likely to result in the death of both of them. If the twins are discovered after 40 days of gestation, very experienced stud vets may attempt to eliminate one of them by guiding a sterile needle through the wall of the vagina and into the foetal sac under ultrasound guidance. 3) Abort the pregnancy and start again. This is only possible up to 35 days when the endometrial cups develop. After 35 days, the pregnancy can be aborted but the mare is unlikely to return to fertile oestrus within the same breeding season. Abortion Undetected twin pregnancies often end in abortion. If this occurs late in pregnancy, there is a possibility of problems during delivery which can lead to loss of the mare. Twins that are born alive are usually underweight and need a great deal of care. It is common for one or both of them to die within a few days of birth. Those that survive are less likely to achieve a high level of performance than single foals. |
