Mastitis in cows: Symptoms and treatment
Mastitis is a disease that is present in virtually every dairy herd in the world to some degree. One third of all cows have it. This disease costs farmers an estimated $200 per cow annually in control, treatment, reduced milk production and discarded milk. This disease causes the largest economic loss to dairy farmers than any other disease.
What is mastitis?
Simply stated it is an inflammation of the mammary gland. A cow's udder is divided into four quarters (four glands). These quarters are self-contained; there is no mixing of milk between them. Each quarter has a teat that opens and closes by way of a teat sphincter. Because of udder anatomy usually only one quarter is affected at a time.
Mastitis can be caused by microbial infection, physical injury to the teat or chemical irritation. The latter two often subsequently develop bacterial infections. Bacteria enter through the teat sphincter and thrive on the gland's milk as its growth medium. Bacteria are the organism most frequently implicated but it can also be yeasts, mycoplasms and, infrequently, algae.
Mastitis can be classified as contagious or environmental. Contagious mastitis passes from cow to cow through unsanitary milking protocols. The environmental variety is picked up from the cow's area such as soiled bedding or farm ponds. It is important to discover which type has been contracted as control methods are different.
Mastitis is ranked in severity as acute, chronic or sub-clinical. Acute is sudden onset with severe symptoms. Chronic is a long-term, possibly recurring infection. Sub-clinical is not observed but discovered through routine testing of the milk. Sub-clinical cases outnumber clinical case by 15-40 times and account for the majority of economic impact through long-term reduced milk production.
Clinical Signs and Treatment
The signs of clinical mastitis include a hot, swollen or painful quarter and clots or flakes in a serous milk. A nursing cow may show a reluctance to allow her calf to nurse.
A cow with clinical mastitis should be stripped of her milk frequently to deny the bacteria its growth medium. The teat should be sterilized with an alcohol preparation then all milk removed. This is followed by an antibiotic given in the teat halfway up the streak canal (intramammary infusion). The infusion pushes the antibiotic into the teat cistern and should be massaged from the outside. Oxytocin can also be used to cause frequent complete milk let-down to speed the healing process. All milk during the infection and treatment time should be discarded.
A sub-clinical mastitis is treated with the antibiotic infusion when the cow is no longer lactating. A cow that is resistant to the treatment or seems to become re-infected frequently should be culled from the herd as she is a reservoir of bacteria constantly re-infecting others.
Vaccines for specific organisms have been developed but they are of limited value. They do not prevent mastitis, they limit the severity of an outbreak once it has occurred. They also don't cover all types of organisms. Research in this area is ongoing.
To control contagious mastitis the teats should be dipped in germicide before and after milking. The milking equipment should be kept clean. All cows should get a dry antibiotic treatment once they stop lactating as a preventative to sub-clinical disease.
Environmental mastitis tends to be resistant to antibiotic treatment so cleanliness is paramount. The cows' bedding and other places they lie down should be kept free of manure, urine and mud. Their udders should be shaved to keep them free of manure caught in the hair. After milking, the teat sphincter remains open for about 30 minutes. This is a prime time for bacterial introduction from the environment, so a cow should be kept standing for this time period. This can be achieved by feeding them after milking. As with all farm management, a well-planned control program is the best way to prevent mastitis.
UC Davis Veterinary Medicine
Louisiana State University Agriculture Center
Lactation Biology Website