EP271

Mastitis in the Ewe

by
Helen A. Swartz, Ph.D, State Sheep, Goat and Small Livestock Specialist


DEFINITION
Mastitis is defined as an inflammation of the mammary gland or udder of the ewe. The term mastitis is from the Greek word mastos, for breast, and itis, for inflammation of. The response to injury to the udder of sheep is called inflammation. Mastitis is the reaction of milk -secreting tissue to injury produced by physical force, chemicals introduced into the gland or most commonly from bacteria and their toxins.
To clarify the discussion on mastitis, the following definitions are given:
Udder infection -The udder cavity is invaded by microorganisms which cause inflammation.
Subclinical mastitis -No swelling of the udder is detected nor is there observable abnormalities in the milk. Special screening tests, however, such as the California Mastitis Test (CMT), Wisconsin Mastitis Test (WMT) and the catalase test will show changes in the milk. This type of mastitis is referred to as "hidden." It is based on an estimation of somatic cell counts.
Clinical mastitis -Can be mild or acute, and there is the presence of leukocytes (white blood cells) in the milk.
Mild clinical mastitis involves abnormality in the milk such as flakes, clots, and a watery or other unusual appearance. A hot or sensitive udder may be slight or absent, however there may be signs of swelling.
Severe clinical mastitis involves a hot, hard sensitive udder that is quite painful to the ewe. The onset is sudden and the ewe may become ill showing signs of fever (105° -107° F), rapid pulse, depression, weakness and loss of appetite. When the whole system of the ewe is affected, the condition is referred to as acute systemic mastitis or bluebag.
Milk production by a ewe with a bluebag has usually ceased and the lambs will need to be reared as orphans or grafted on another ewe.
Chronic mastitis -A persistent udder infection exists most of the time in the subclinical form occasionally can develop into the clinical form before returning to the subclinical. The results are hard lumps in the udder from the "walling off" of bacteria and the forming of connective tissue.

MAMMARY GLAND SYSTEM
Among domestic animals, the cow, sheep and goat have the simplest mammary gland system. Development of the mammary gland in the sheep and goat is identical to that of the cow (Schalm, et. al., 1971). The teat has a single opening leading into a teat sinus which is continuous with the gland sinus above which a number of large ducts empty. (Figure 1)

GENETIC FACTORS
There are a limited number of studies on the influence of heredity on resistance or susceptibility to mastitis in either the cow, goat or sheep. Genes are known to influence the shape and structure of the teat (Hickman, 1964). Mastitis histories of two cow families in different geographical locations revealed significant difference which led to the conclusion that heredity played a part in the infection rate. Dam-daughter comparisons based on data derived from field surveys cite the influence of heredity on mastitis (Randel and Sunberg, 1962).

MICROORGANISMS-PRIMARY CAUSE OF MASTITIS
The primary cause of mastitis in cattle, goats and sheep are well-recognized groups of microorganisms, Streptococcus sp., Staphylococcus sp., Pasteurella sp. and coliforms, Escherichia coli, Enterobacter sp., and Klebsiella sp. Recent studies at the University of Missouri collected data on the incidence of subclinical mastitis in ewes and identified Staphylococcus, sp., Streptococcus sp. and Micrococcus sp., found in bacterial cultures (Andrews et al., 1985). Nineteen microorganisms have been
identified as causative agents of mastitis in cattle. Yeast and fungus have also been found frequently infecting the udder, but usually go unnoticed because they produce a mild or subclinical mastitis.
The relationship between the amount of mammary tissue affected by microorganisms and the form of mastitis is shown in figure 2.

CONTROL OF MASTITIS
One of the most important keys to controlling mastitis in ewes is good management practices. The incidence of mastitis is greater in closely confined flocks. Bedding material in barns should be clean, especially before and after lambing. Microorganisms thrive in dark, wet, warm bedding. When the ewes lay down to rest, the bacteria in dirty bedding can easily enter the teat when the udder is full of milk. Microorganisms can enter the teat canal. Dirty bedding and crowding will make this possible. Lambs from infected ewes will often nurse other ewes, spreading the microorganisms to others in the flock. Isolating ewes suspected of chronic or acute mastitis will help reduce the incidence of mastitis in a flock. Ewes should be fed in bunks rather than on the ground.

MANAGEMENT
Ewes with udders that show obvious signs of acute or chronic mastitis should be separated from the flock and treated with antibiotics. Then lambs often need to be bottle fed. Milk production may be decreased significantly or slightly depending upon the degree of infection.
Chronic mastitis can be prevented by a good management program. Before weaning cut out all grain feeding for 3-5 days. Feed a lower quality substitute such as grass hay at this time. Reducing water and all feed 12-24 hours before weaning is sometimes practiced. Reducing the volume of milk by reducing grain and feeding low quality hay will help prevent udder distension and fever. Microorganisms will have more difficulty infecting a flaccid udder. In addition, the tissue in the udder will not be damaged, preventing vulnerability to microorganisms.

TREATMENT OF MASTITIS
Disinfect the teat end with alcohol and infuse a tube of mastitis antibiotic through the teat canal. Give the ewe an injection of a combination of penicillin, dihydrostreptomycin, dexamethasone and an antihistamine. The antibiotics should affect the microorganisms and the dexamethasone and antihistamine should help the tissue heal and reduce inflammation.

CULLING
The udders of ewes should be examined physically for hard lumps after weaning and before breeding.
Ewes with "lumpy bags" should be culled. The supply of these ewes will be decreased and the amount of decrease will depend upon the amount of tissue damaged. The genetic factor involved should also be considered. Culling these ewes and practicing good management should result in a low incidence of mastitis.

REFERENCES
Schalm, O.W., E.J. Carroll, and N.C. Jain. 1971.
Bovine Mastitis, Lea and Febiger, Philadelphia p.24.

Hickman, C.G. 1964. Teat shape and size in relation to production characteristics and
mastitis in dairy cattle. J. Dairy Sci., 47:777.

Randel, J., and F. Sunberg. 1962. Factors influencing the type and incidence of mastitis
in Swedish dairy cattle. Acta Vet. Scand. 3:13 Suppl. 1.

Andrews, M.L., T.A. Mollett, R.T. Marshall and D.H.Keisler. 1985. Incidence of subclinical
mastitis in ewes and impact on lamb performance.
Missouri Sheep Report, University of Missouri and Lincoln University. Nov/85.