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Non Infectious Causes

Seasonal infertility
(176) 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.

A catabolic state
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.

Light
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 produce 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.

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:

  • Ultra violet radiation may cause regression of the corpus luteum particularly in white breeds. The outdoor breeding female should always be derived from at least one pigmented parent.
  • Provide extensive shades so that the sows can protect themselves from the sun.
  • Site the arks in the wind direction so that with open ends cooling can take place.
  • Provide extensive well maintained wallows suitably sited so that sows do not have too far to reach them.
  • Always maintain boars within the sow groups for the first six weeks of pregnancy at least.
  • Increase feed intake from days 3 to 21 after mating.
  • Increase the mating programme by 10-15% over the anticipated period of infertility.
  • Because boar semen can be affected follow each natural mating 24 hours later by purchased AI.
The boar
A third part of the equation involves the presence of the boar and his pheromones or male chemical hormones. Pheromones are required to maintain pregnancy in individual susceptible disadvantaged sows.

Boar presence in the dry sow accommodation is recommended from the day of service through to the day of farrowing. The boar should be mixed in or have access to the group for at least the first 21 days of pregnancy. There is clear evidence that this will improve farrowing rates particularly if they are associated with summer infertility. If sows are individually housed the boar should be allowed to move down the passages and make social contact daily.

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