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Abortion and Seasonal Infertility
Embryo loss and abortion(619) Embryo loss occurs when there is death of embryos followed by absorption, or expulsion. Healthy embryos grow into foetuses. Abortion means the premature expulsion of a dead or non-viable foetus. There is often alarm when an abortion is seen but it should be remembered that there can be loss of embryos at any time during early pregnancy, which often goes unseen.
Embryo loss or abortion can be considered in three main groups: First, during the period from fertilisation to implantation; second, during the period of implantation at around 14 days post-service to 35 days; and finally, during the period of maturation, which results in premature farrowings. It can be seen therefore that losses can take place at any stage from approximately 14 days after mating, when implantation has taken place, through to 110 days of pregnancy.
The maintenance of pregnancy
Pregnancy is maintained due to hormonal changes initiated by the implantation of embryos at day 14. These changes allow the corpus luteum (the body from which the egg is released) in the ovary to develop and produce the pregnancy hormone progesterone. The presence of the corpus luteum is necessary to maintain the pregnancy throughout the whole of the gestation period. The loss or failure of the corpus luteum through any cause initiates the farrowing process, hence an abortion, or if near to term a premature farrowing.
Methods of Investigation
It is worthwhile monitoring the levels of abortion in your herd continually and comparing them to the normal levels. The following information should be recorded with each abortion: It is important to study the herd history and environment. For example, is there a seasonal effect or an association with a particular area of the housing or management practice? You should also note the clinical state of the sow at the time of abortion. Does she show other clinical signs or is she apparently normal? You should examine the aborted foetuses too. Are they fresh with no signs of any decomposition, or are they decomposing or mummified. Such observations, particularly if recorded over a period, may be of help to your veterinarian in leading to a possible diagnosis of the cause.
There are three parts to the investigations that must be carried out. First, collect information about the individual sows, then request post mortem examinations and serological tests, and finally, assess the clinical evidence and feeding procedures in the herd.
The object of these is to identify the area of failure and by management studies, examination of records, clinical examinations, and laboratory tests the cause may be identified.
Non Infectious Causes
Seasonal infertility
A catabolic state
Light
Abortions, anoestrus and sows found not in pig commonly occur during the period of summer infertility when sunlight is intense and the weather is hot. This is particularly evident in outdoor sows where levels of pregnancy failure may reach 15-30%. In such cases the abortions are so early that the foetuses are either not seen or there is progressive embryo mortality and a delayed return to oestrus. Look for slight mucous discharges from the vulva and if present refer to chapter 6 Endometritis.
The following factors are important indoors or outdoors as applicable (Fig.14-8): Changes in energy requirements as shown in Fig.14-9 may result in luteolysis or regression of the corpus luteum and abortion. Abortions can also be associated with specific infectious diseases or mouldy feeds. See also chapter 6.
If you are using the farrowing rate loss analysis sheet illustrated in chapter 5 you will be doing most of this anyway.
Experiences have shown that 70% of all abortions fall into this category. Because the sow historically only produced one litter per year, with farrowings during early spring, there is an in-built tendency for the animal not to maintain a pregnancy during the summer and autumn periods. This is well recognised with summer infertility and the autumn abortion syndrome, where environmental factors are likely to cause the corpus luteum to disappear.
If the metabolism of sows are allowed to progress to a negative energy or catabolic state so that they are having to use their body tissues to maintain the energy equilibrium, then individual susceptible animals may abort. Clinical examinations will identify possible changes in the environment. For example, the removal of bedding, poor quality feeds, or a drop in feed intake. The latter may simply be associated with a change in stockpeople. Outbreaks of abortion may occur when there are changes from pellet feeding to meal feeding, or where feed is presented by volume and not by weight. Wet, damp environments or high air movement cause chilling and increase demands for energy. An important feature of environmental abortions is that the sow remains normal, often eating feed in the morning, and expelling the litter in the afternoon. Some people call these Farrowing abortions". The aborted foetuses are perfectly normal and the sow shows no signs of illness. The underlying initiating mechanism is regression of the corpus luteum.
Another contributing factor is decreasing daylight length. To maintain a viable pregnancy requires constant daylight length. Ideally this should be 12-16 hours per day. Light intensity experienced by the sow can be affected by a number of environmental inadequacies, for example, poor lighting in the first place, followed by fly faeces and dust on lamps gradually reducing the availability of light. High walls surrounding animals, or automatic feeders in front of sows producing shadows. A simple tip here is to make sure that you can read a newspaper in the darkest parts of the building at sow eye level. If not, then problems may start. Painting the roofs and walls white to increase the reflection of light is one way of improving the environment and on a number of occasions abortions have ceased after such simple improvements.
