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Diseases Affecting Reproduction

(200) The previous chapter has reviewed the various management and environmental factors that have an adverse affect on reproductive efficiency. The description of the diseases here concentrates on their effects on reproduction but in some of them infertility is only part of a much broader picture. In such cases references to specific chapters are given. There is often an overlap between infectious and non infectious infertility and in many cases the two are interrelated. It is important to determine if there is an infectious component to a problem in a herd because corrective measures may involve both treatment and management procedures. Fig.6-1 demonstrates a pathway that can be used to identify the causes of an infectious infertility problem. It asks the question what diseases are present in the herd, because any one of these may have an occasional effect. Such diseases are listed in Fig.6-2 and Fig.6-3. For example, if a herd is infected long term with aujeszky's disease virus, porcine parvovirus (PPV), porcine reproductive and respiratory syndrome (PRRS) or swine influenza (SI) then at varying intervals following the initial herd outbreak there may be reproductive failures, albeit in many cases at individual sow levels. If a herd is free from these infections and then become infected with one of them an acute episode of that disease will occur. This will be manifest by reproductive failure including increased numbers of abortions, repeats on a normal and abnormal cycle and in the case of those viruses that cross the placenta, there will be foetal death, mummified and stillborn piglets.

Diseases such as porcine parvovirus (PPV), PRRS and leptospirosis may infect the sow without causing other clinical signs. Usually in such cases the disease picture is sporadic (unless it appears for the first time) and a detailed examination of records helps to clarify this.

There are nine main viruses that can cause reproductive disease, but only five of these are really important in those countries where they occur. The five are:

  1. Aujeszky's disease (AD) virus or pseudorabies virus (PRV).
  2. Porcine parvovirus (PPV).
  3. Porcine reproductive and respiratory syndrome virus (PRRS).
  4. Classical swine fever virus (CSF).
  5. Swine influenza virus (SI).
Bovine viral diarrhoea virus (BVDV) border disease virus (BDV) and enterovirus (SMEDI) may cause sporadic reproductive problems but in most countries disease would be uncommon. Encephalomyocarditis virus (EMCV) varies in its pathogenicity in different regions of the world. In Europe it is rarely implicated in porcine disease, in the Caribbean it causes heart problems but in North America it is associated with reproductive problems

Most bacteria are opportunist invaders and usually only affect a few individual breeding females, a good example is erysipelas. The exceptions are leptospirosis and brucellosis which are herd problems.

Some of the clinical signs and pathological effects that viral and bacterial agents have on fertility are shown in Fig.6-2 and Fig.6-3.

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