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Abortion and Seasonal Infertility

Embryo loss and abortion
(175) 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.

Abortions and their cost
Natural biological failures of pregnancy due to a variety of causes occur across all species. In healthy normal sow herds abortions observed by the stockpeople are normally less than 1 per 100 pregnancies. The cost of an abortion can be calculated quite easily, taking into account the cost of feeding the sow during a pregnancy period and the loss of margin over feed on the loss of the piglets. For example, with feed costing £160 per tonne and 2.2 litters per sow, per year it would have cost £72 in feed to produce a litter. 10 pigs reared in the herd at a margin of £25 per pig over feed would have yielded £250, giving a total cost per abortion of £322 if it occurred near the end of the pregnancy period.

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:

  • Sow number.
  • Parity.
  • Boar used.
  • Date of service.
  • Date of abortion.
  • Housing.
  • Feed and amounts given.
  • Clinical observations of the sow and any disease history.
  • Condition of the aborted piglets - alive fresh, recently dead or mummified.
If you are using the farrowing rate loss analysis sheet illustrated earlier in this chapter you will be doing most of this anyway.

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.

Post-mortem and laboratory examinations
Fresh, aborted foetuses should be submitted to a competent diagnostic laboratory where examinations can be carried out for evidence of viral and bacterial infections, together with histological examinations and toxic studies. In many cases the end results of post-mortem and serological tests do not identify any particular infectious organism, which may seem disappointing. However, it is useful in telling us what is not present.

Clinical examinations
Of all the examinations carried out, clinical observations are perhaps the most important. Look at the environmental factors in Fig.5-29. Are any of these important? By using the recorded information on individual cases and collating this to the problem group of sows, it then may become possible to differentiate clinically between an infectious and a non infectious cause. Fig.5-23 indicates the likelihood of either of these.

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