Mastitis in Dairy Cattle

Mastitis is the inflammation of the mammary gland which generally occurs as a result of white blood cells being released - the body’s response to invasion by bacteria, usually via the teat canal. Over 200 different micro-organisms have been shown to cause intramammary infections, but most of the economic losses are associated with staphylococci, streptococci and coliform bacteria. The microorganisms that most frequently cause mastitis are often categorised as either environmental or contagious pathogens, although organisms can show characteristics of both groups.

Exposure of the teat surface to environmental bacteria occurs mainly between milking times. Sources of environmental bacteria such as Strep. uberis, include faeces, genital discharges, bedding material, feedstuffs, soil and water. These bacteria cannot practically be eliminated from the cow’s environment, and the teat-end in particular is often in prolonged and close contact with some of these materials. Once udder infections with these environmental bacteria are established within the herd, transmission from infected quarters to other quarters and cows can occur at milking time.

Contagious bacteria often stem from an infected udder. However, bacteria such as Staph. aureus also readily colonises the teat canal and chapped or sore teat skin and may survive at other sites on the cow. Contagious bacteria are primarily spread at milking time, when bacteria from infected quarters is spread to other quarters by splashes of milk during stripping, or by the hands of operator’s and milking machines.

Clinical (visible signs or symptoms) mastitis is usually diagnosed by clots in the milk, or swelling and/or heat in a particular quarter or the udder as a whole. Subclinical (no signs or symptoms) mastitis is detected and diagnosed by examination of a bulk milk tank sample for Somatic Cell Count (Herd Test), or by culturing (by the farmer, by the vet, or by a laboratory) for the presence of mastitis pathogens.

Losses from subclinical (no signs or symptoms) and clinical (visible signs or symptoms) mastitis can mainly be attributed to decreased milk production, however to evaluate the full cost of a case of mastitis what must also be taken into account is both the direct costs (discarded milk, the cost of treatment, culling) and indirect costs (production losses, supplier penalties, labour costs).

Mastitis is generally treated by an intramammary or injectable antibiotic, as recommended by your vet. The Virbac New Zealand range of mastitis treatments includes both intramammary and injectable products — all of which were developed in NZ, are made in NZ, and in most cases, were trialled in NZ.

For more information on mastitis or the Virbac range or mastitis treatments, talk to your vet.