What is mastitis?
Mastitis is an inflammation of the mammary gland, usually caused by bacterial infection. It is both of economic and welfare concern because of direct and indirect costs and because it is a painful disease that affects ewes and lambs. Mastitis can be sub-clinical, acute or chronic. Visible signs of disease are apparent in cases of acute and chronic mastitis but there are no clinical signs in sub-clinical infections.
Types of mastitis
Sub-clinical mastitis leads to reduced milk yield and so slower lamb growth rates. It is more common as ewes get older, and in ewes of 6 years or more the affect of sub-clinical mastitis is more marked with lambs growing more slowly and often needing supplementary food.
All ewes have bacteria in their udder, but they are not necessarily diseased. Research in our group is exploring the bacteria in healthy and diseased udders to understand differences between them.
Ewes with acute mastitis are noticed because they do not come to the trough to eat, stand away from the flock, appear lame because of a painful udder or refuse to let their lambs feed. The affected udder can be hot, swollen and painful, or cold and discoloured. Milk might be watery or pusy or contain blood. Farmers report between 0% and 5% of ewes in the flock have acute mastitis per year, the average is about 1%. High levels of clinical mastitis are worth investigating to implement a control programme.
Chronic mastitis can be detected as lumps, or masses, in the udder that feel different from normal udder tissue. The masses are abscesses caused by bacteria; they can be any size or shape. They can rupture and reform, so may not be present every time the udder is palpated. Farmers report culling an average 2 – 8% of the flock with udder masses at weaning.