Due
to infectious or non infectious, non specific and specific causes.
Infectious Causes:
Whenever there is infection, it alters the environment of uterus
that will impair the transport of sperm, death of sperm or ovum;
even if fertilization occurs then there could be embryonic death as
environment is hostile for the development of embryo. Even the
struggle is continued but abortion may occur.
Specific infection:
The
infection which particularly affects reproductive tract so those
infections whose predilection site is reproductive tract e.g.
brucellosis, trichomoniasis.
Non
specific infection:
Staphylococcus, streptococcus, E.coli, pseudomonas. These are
opportunist pathogens. Specific infection does not require
predisposing factors where as non specific requires it. Specific
infections are enzootic in nature, when come in herd affect all non
specific and are sporadic in nature
For
the development of non specific infection two barriers which prevent
its development
-
Physical barrier
-
Defensive mechanism
Physical barrier:
-
Cervix
-
Vulvular sphincter
Barriers are predisposed at different occasions as:
-
Estrous or insemination
-
Parturition
At
both these occasions reproductive tract is in its most resistant
form. When uterus is under the influence of estrogen then it is most
resistant to infection and at the time of parturition there is
increased level of estrogen. So uterus is resistant to infection but
when progesterone is dominant, uterus is prone to infection.
How
the development of infection is prevented by estrogen:
-
There is increased blood supply to uterus so more white blood
cells
-
Maximum production of secretions mucous which is flushing effect
and dilute the pathogens
-
Contractions are going on so pushing the contents of uterus
outside
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