Michaela Giles investigates the huge topic of infertility in pigs, and provides a practical overview of the problem and its many and varied causes
There are two types of infertility that can affect pigs, infectious and non-infectious, These are sometimes described as acute reproductive problems and chronic reproductive problems respectively, although there is some overlap. While the outcomes of either may be similar, the root causes are quite different, and will usually have different diagnoses and responses.
Farmers are often keen to blame a chronic condition with an infectious cause, as there’s a clear management pathway for known infectious causes. However, this is rarely the case. Chronic causes may be also harder to isolate and, possibly, will have a few varied origins leading to a cumulative infertility response.
Broadly speaking, acute reproductive problems are usually described as the sudden onset of problems associated with abortions, stillborn pigs or premature litters. These all usually have an infectious cause (viral, bacterial or parasitic), as illustrated in Table 1.
Infectious organisms can bring about abortion in three ways.
By invading the placenta, causing inflammation and possibly necrosis (tissue death), effectively eliminating the nutrient and oxygen supply to the foetuses.
By invading the foetuses and killing them.
By multiplying elsewhere in the body, causing fever and, on occasions, toxaemia (toxins in the blood).
Additionally, there’s a second group of bacteria which can be described as ‘opportunist invaders’, which have the ability to cause embryo mortality or abortion in individual sows and, sporadically, in small groups of sows – they do not spread through the herd and are often mixed infections (i.e. several different species involved).
If these opportunist bacterial infections occur in a sufficient number of sows, they can become a herd problem. These opportunists are often commensal; normal inhabitants of the vagina or the boars’ prepuce, and so their presence upon laboratory identification requires careful interpretation. What appears to happen is high numbers of commensal bacteria (eg Klebsiella, Streptococci, Staphylococci), are deposited deep into the vagina by the boar in such numbers that they can establish an infection, particularly towards the end of a season.
Examination of sows between 14 and 21 days post-mating will sometimes reveal a tacky discharge on the vulva which may not be very obvious. Should they return to cycle at 21 days, or return out of cycle 21+ days, it may be indicative that embryo loss is taking place.
Chronic reproductive failure is usually exhibited by longer-term, low farrowing rates, low live births and/or a high number of animals failing to conceive. The cause of these sorts of problem is most often non-infectious and, while there are many possibilities, these causes can be broadly assigned into three groups; toxic effects, impairment and management factors (once again, refer to Table 1).
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