The organisms infecting the udder of goats are similar to those in cows. Coagulase-negative staphylococci are generally the most prevalent and can cause persistent infections that result in increased cell counts and low-grade mastitis with some recurring clinical episodes. The level of infection and incidence of mastitis due to Staphylococcus aureus tends to be low (<5%) but can result in persistent infections that do not generally respond to therapy. Streptococcal intramammary infections can occur in both subclinical and clinical cases but are usually much less frequent than in cattle. Streptococcus agalactiae is not a common pathogen of mastitis in does.
Mycoplasma infections, primarily M mycoides (large colony type) and M putrefaciens, sometimes cause serious outbreaks of mastitis in goats (see Contagious Agalactia). The latter also causes septicemia, polyarthritis, pneumonia, and encephalitis, together with serious disease and mortality in suckling kids. M capricolum has also been reported to cause severe mastitis in goats and infection in kids. Does usually recover in ~4 wk.
As with cows, gram-negative organisms cause intermittent infections that may be severe but are usually self-limiting. Trueperella(formerly Arcanobacterium) pyogenes sometimes produces multiple, nodular abscesses.
Does can also exhibit signs of mastitis from caprine arthritis and encephalitis (see Caprine Arthritis and Encephalitis) and ovine progressive pneumonia (see Progressive Pneumonia in Sheep and Goats) secondary to systemic infection. Agalactia is common, as is a hardening of the udder from fibrosis.
Programs for diagnosis, control, and treatment of bacterial mastitis in goats are similar to those in cows. However, monitoring subclinical mastitis with somatic cell counts (SCCs) in does is difficult because of poor discrimination between infected and noninfected animals, especially in the later stages of lactation. This is partially because a higher proportion of cells are epithelial in origin in goat milk than in cow milk. As lactation progresses, shedding of epithelial cells into milk increases; thus, SCCs >1,000,000 cells/mL are common in uninfected does in late lactation. Proper milking procedures and good environmental sanitation are needed to reduce the prevalence and spread of infection. Chronically infected goats should be culled, as should goats with M mycoides infections and those that do not recover from M putrefaciens or M capricolum infections.
Last full review/revision October 2014 by Ronald J. Erskine, DVM, PhD