A Veterinarian’s Perspective:
The prevention and treatment of mastitis are of the utmost concern in dairy cattle, dairy goats, and dairy sheep. In our Shetland flocks, however, we rarely think about mastitis until we have a ewe with an udder problem causing stress in our lives. There are several different types of mastitis, with different possible treatment strategies and different possible outcomes. Prevention of mastitis is always the ultimate goal, and early recognition of mastitis and aggressive treatment give the best hope for a positive outcome.
Contagious mastitis is the number one concern with dairy animals, but is not a serious concern in our Shetland flocks. There are several types of bacteria that cause contagious mastitis, with the predominant type being Staphylococcus species. Contagious mastitis is spread at milking time, often by contaminated milking equipment or improper milking procedures. Adhering to a strict and sanitary milking protocol is the best prevention for contagious mastitis.
Acute mastitis is usually Coliform mastitis, also known as Environmental mastitis. Commonly coliform bacteria such as E.coliand Klebsiellaspecies are found in dirty lambing environments, and infect the udder in the immediate post-partum period. The affected ewe will have a sudden onset of anorexia, fever, depression and lethargy. She may appear shocky, weak, with a high heart rate. The udder is hot, red, swollen and can be edematous. The milk usually has an abnormal color, looks thin and yellow or bloody, or occasionally will be thick with chunks.
Acute mastitis must be treated within 4 to 6 hours of onset of symptoms for the best possible outcome. Untreated, acute mastitis can cause loss of the affected portion of the udder, gangrenous mastitis, and/or death. Treatment for acute mastitis usually includes an anti-inflammatory drug such as Banamine, systemic antibiotics given intravenously, and frequent milking out of the affected side of the udder. If an affected ewe is extremely toxic or shocky, intravenous fluids can be administered. Treatment of acute mastitis should be performed by the flock veterinarian or an extremely experienced shepherd under the guidance of the flock veterinarian. Prevention of acute mastitis is best accomplished by keeping an extremely clean lambing pen.
Gangrenous mastitis is also known as “Blue bag” and can be a sequela to an environmental mastitis or a lamb-induced teat injury. Staphlococcus aureus and Pasteurella hemolytica are often involved with gangrenous mastitis. Occasionally a case of gangrenous mastitis may be seen in association with a P.hemolyticapneumonia outbreak in lambs.
Gangrenous mastitis occurs when the bacterial toxins cause blood clots in the vessels of the affected side of the udder. The loss of circulation leads to gangrene, and the udder will turn cold and blue as the infection progresses. The affected portion of the udder eventually sloughs off, and long-term systemic antibiotic and anti-inflammatory therapy is necessary to save the life of the ewe. Survivors are usually culled, unless they have a high genetic or emotional value, and the shepherd is willing to bottle-raise future lambs.
Subclinical mastitis is one of the most common causes of culling animals from the flock. It is a chronic, insidious, low-grade infection that is caused by a variety of environmental bacteria. Dirty environmental conditions in the lambing area, extremely muddy pastures, and poor nutrition can all play a role in the development of subclinical mastitis. Affected ewes may appear fairly normal, but significantly decreased milk production can be seen as poor lamb growth or neonatal malnutrition and/or death. When the udder of the affected ewe is examined it is usually slightly swollen and hard. Occasionally udder abscesses are seen. Again, affected ewes are usually culled, unless they have a high genetic or emotional value, and the shepherd is willing to bottle-raise future lambs. Prevention of subclinical mastitis is best accomplished by keeping a clean barn, keeping animals out of extremely wet or muddy areas, and by ensuring good nutrition.
Chronic Indurative Mastitis of Sheep is a form of subclinical mastitis caused by the OPP virus. The udder appears full but has a hard/firm texture upon palpation. Milk production is markedly decreased, and poor lamb growth is usually the first sign of the disease. Symptoms can begin after the first lambing, but usually are seen in ewes older than 3 years of age. Definitive diagnosis can be made by blood testing for the OPP virus. The flock veterinarian should be involved in testing and creating a flock management plan for OPP.
Functional mastitis is the one of the most common forms of mastitis that I have personally seen in Shetland sheep. This type of mastitis tends to occur in the ewes that are high milk producers with very large udders. If a single lamb or both twins are nursing on only one side of the udder, the teat on the opposite side can become engorged and too large for the lambs to nurse upon. If the situation is caught fairly quickly, aggressive and frequent milking out of the affected side will solve the problem. If the situation goes unnoticed, the affected side of the udder becomes hot and red and mastitis develops. Treatment with systemic antibiotics and anti-inflammatories may be necessary, along with frequent milking. The best prevention measures for functional mastitis are close observation in the lambing pen, and avoiding absolute over-feeding. Studies have shown that grazing excessively lush pastures and/or feeding practices that favor excessive milk production will predispose ewes to mastitis.
Mastitis due to teat injuries is seen occasionally in Shetland sheep. Teat injuries need to be treated immediately to minimize the potential for mastitis. Severe teat injuries can lead to loss of all or a portion of the udder, and culling the ewe may be necessary.
Mastitis due to udder abnormalities or poor udder conformation is seen, albeit rarely, in Shetland sheep. These ewes should be removed from the breeding program, as udder abnormalities and conformation may be passed on to their offspring.
As we can see, prevention of mastitis in our Shetland ewes is best accomplished through good animal husbandry. A clean environment, especially at lambing time, good nutrition and well-balanced rations, and close observation of our ewes and their udders are all key to mastitis prevention. It is also extremely important to examine the udders of any potential additions to the flock for problems before making the purchase and bringing the new ewes home.
©Dr. Heather Ludlam DVM