TREATING MASTITIS WITHOUT ANTIBIOTICS

Mastitis

Mastitis is a disease that affects a large number of dairy cattle throughout the world. A survey conducted in the major milk-producing countries indicates that each year clinical mastitis afflicts 15% to 20% of cows³⁵. In Canada and the United States, it is thought that 50% of cows have one or more infected quarters. In Denmark, it is estimated that mastitis is the cause of 30% to 40% of veterinary interventions.
Using antibiotics is not an ideal solution. Other than the problems they cause with the milk (withdrawal for x days, contamination from antibiotic residues, problems associated with yogurt and cheese processing), antibiotics have not reduced the incidence of mastitis (footnote A)³⁷. Problems associated with resistance or even ineffectiveness are quite real in the case of mastitis caused by coliforms and Staphylococcus aureus¹⁵.
In organic agriculture, the use of antibiotics is neither normally authorized, nor desirable. There are however a large number of preventive and curative measures available to producers to deal with the problem. Mastitis control also entails a good understanding of the factors that encourage its incidence and the microorganisms that cause it.


Figure 1. Factors influencing the incidence of mastitis.

A. The incidence of contagious mastitis has diminished through the use of antibiotics, but this has been paralleled by an increase in the level of environmental mastitis. Table 1 shows the difference between these two types of mastitis.

TYPES OF MASTITIS

Since mastitis is a disease that has different levels of intensity and may be caused by different organisms, there exists a complete lexicon to describe the disease. Indeed, there are a number of types. It is therefore important to be able to recognize the different types of mastitis in order to decide what preventive measures or treatments to use. To clarify the terms used throughout this article, Table 1 provides the definitions and characteristics of the different types of mastitis.
Table 1 - Characteristics of the different types of mastitis

Types of Mastitis	Characteristic Symptoms or Definition
Acute clinical	Inflammation of the teat, fever above 39C, weak and dejected animal, lack of appetite. Drastic drop in milk yield. Often follows calving and, less seriously, after cow goes dry.
Hyperacute clinical	Swollen, red, painful quarter. Milk passes with difficulty. Fever over 41C. Cow has no appetite, shivers and loses weight quickly. Lactation often stops.
Subacute clinical	No apparent change in udder, presence of flaky particles in milk, especially in initial ejection. Subject appears healthy.
Subclinical	No symptoms. 15 to 40 cases for every clinical case. Milk appears normal. Only change is detection of pathogenic agent in analysis and increased somatic cell count. Mostly caused by Staphylococcus aureus.
Chronic	Repeated but mild clinical attacks, generally without fever. Lumpy milk, quarters sometimes swollen. Quarter may become hard (fibrous indurations). Antibiotic treatments often do not work.
Gangrenous	Affected quarter is blue and cold to the touch. Progressive discolouration from the tip to the top. Necrotic parts drop off. Cow often dies.
Contagious	Mastitis caused by bacteria such as Staphylococcus aureus and Streptococcus agalactiae, of which other infected cows are the main source.
Environmental	Mastitis caused by bacteria such as coliforms (e.g. E. coli), of which the main source is a contaminated environment, i.e. manure.

MICROORGANISMS CAUSING MASTITIS

There are a great number of microorganisms on and in cow udders. Watts⁵² identified 137 species and subspecies of microbes that can be associated with the mammary gland of the cow. Several of them are part of the normal flora and, with few exceptions, do not cause mastitis (footnote B). On the contrary, they may protect udders from infection caused by pathogenic bacteria.
Several other microorganisms may, however, cause infection in the mammary glands. The most common, those that cause about 90% of mastitis infections, are given in Table 2. There are contagious microorganisms and environmental microorganisms. Infected cows are the main source of contagious microorganisms, which survive and proliferate on the skin and on teat wounds. They consist of Streptococcus agalactiae, Staphylococcus aureus and Streptococcus dysgalactiae. Environmental microorganisms (Escherischia coli and other coliforms, Streptococcus uberis) do not remain on the teat. Rather, their presence indicates a high degree of contamination of soil, bedding, and water caused, particularly, by manure.
To infect a quarter, a microorganism must first enter the quarter and the cow must be unable to get rid of it before it multiplies (footnote C). The following is a typical scenario that leads to mastitis infection.

1. Contact with the microbe: The number of microorganisms multiplies near the orifice (or sphincter) of one or several teats. This is where hygiene and milking habits play an important role in preventing microbes from entering the quarter.
2. Entry of microbe into the teats: Entry may be forced by the milking machine, particularly at the end of milking. Injured teats (injuries, keratin injured inside teat) or teats whose openings are too large may be easily invaded. This is where adjusting milking machines and preventing injuries is critical.
3. Immune response of the cow: the cow's first line of defense is to send white blood cells (leucocytes) to eliminate the microbes that have penetrated the teat. If the response is insufficient, the microbes multiply and the cow shows other immune responses such as fever. The effectiveness of the cow's immune system depends on many factors. This is also an area where farmers can do a great deal to ensure good immune response