From the NMC Newsletter "Udder Topics", August 1996
Udder or intramammary infection is the presence of microorganisms that
multiply in the udder. Infections
may be clinical or subclinical, depending on the degree of inflammation.
At times, there is some confusion
during discussions about mastitis because different meanings are applied
to the same term. Therefore, the
following definitions are presented.
Subclinical mastitis is a form of the disease in which there
is no detectable change in the udder and no
observable abnormalities in milk. However, the presence of microorganisms
in milk usually can be
demonstrated by microbiological culture, and inflammatory changes in
the milk can be detected by special
tests, such as conducting a somatic cell count.
Subacute clinical mastitis is a condition in which abnormalities
of the udder and secretion are readily
observable. This form of mastitis can vary in severity, depending in
part, on the microorganism causing
the infection. Changes in the milk, such as flakes, clots, and a watery
appearance are the most obvious
abnormalities. Heat, swelling, and udder sensitivity are slight or
absent.
Acute mastitis is a condition characterized by sudden onset,
redness, swelling, hardness, pain, grossly
abnormal milk, and reduced milk yield. Systemic symptoms may also be
present and include fever, loss of
appetite, reduced rumen function, rapid pulse, dehydration, weakness,
and depression. When the disease
onset is very rapid and the signs are very severe, the disease is termed
peracute mastitis.
Chronic mastitis is an udder infection that is of long duration.
Chronic mastitis may remain in a subclinical
phase indefinitely, or the infection may alternate between subclinical
and clinical phases; at times, clinical
signs may persist for long periods.
Nonbacterial mastitis is a mammary inflammation that occurs when
microorganisms cannot be isolated
from milk samples. Such cases may be either clinical or subclinical.
Source: NMC Publication "Current Concepts of Bovine Mastitis" (1996) pg. 1