Managing mastitis in small ruminants

Any time between giving birth through weaning or dry-off is the ideal time for ewes or does to develop mastitis.

The cost of mastitis is significant due to veterinary costs, milk replacer for lambs or kids that aren’t getting enough milk, culling of relatively young females, increased lamb or kid mortality and the cost of additional creep feed to supplement diets.

Ryan Knuth, Ph.D., University of Wyoming, explained that mastitis is inflammation of the mammary gland resulting from bacterial or viral infection, mechanical trauma or chemical trauma.

Bacteria are the main cause of mastitis, triggering an immune response in the mammary gland.

Mastitis can also be the result of a viral infection, most often due to the virus that causes ovine progressive pneumonia (OPP) in sheep and caprine arthritis and encephalitis (CAE) in goats. Mechanical and chemical trauma are most often seen in dairies due to improper vacuum pressure and chemicals used to disinfect teats.

Mastitis is either clinical or subclinical. With clinical mastitis, there are obvious signs including a firm, swollen udder that is warm to the touch and in some cases, abnormal milk (color, odor or consistency). Teats may be engorged due to lambs or kids not nursing. Females with clinical mastitis often have decreased appetite and/or fever.

It isn’t difficult for mastitis to start. When newborn lambs or kids suckle, bacteria on their faces transfer to the teats, travel upward through the teat canal and potentially cause infection. The presence of feces, urine-soaked bedding and bird and rodent droppings add to the potential for bacterial contamination.

“Some anatomical features help prevent bacteria from infecting the mammary gland,” said Knuth. “At the end of the teat canal, there’s a teat sphincter – a muscle that can close to prevent bacteria from entering the teat canal. However, it takes about an hour or more to fully close after lambs nurse. The teat canal is lined with keratin, a waxy substance that impedes bacterial travel through the teat canal. Keratin also has some antibacterial properties that help reduce bacteria numbers.”

The bacteria most often responsible for mastitis include Staphylococcus aureus, coagulase negative Staphylococci and Streptococcus. Bacteria less likely to be present but can lead to mastitis include Mannheimia haemolytica, E. coli and Bacillus.

“Although these bacteria are associated with mastitis, they are harbored in other body sites and within the environment,” Knuth said. “We can’t just simply disinfect the environment and expect bacteria to disappear. They’re already within the ewe, and she’s always going to be shedding bacteria that contaminate the environment.”

The initial response to bacterial or viral infection appears as inflammation, which helps the body defend itself against invading pathogens.

“This induces local blood clotting, which creates a physical barrier to prevent the infection from spreading into the bloodstream to other body systems,” said Knuth. “This inflammatory response occurs when tissue is physically damaged or pathogens are recognized by the immune system.”

The inflammatory response results in edema, swelling, heat, redness and pain.

Subclinical mastitis can be a significant problem because it’s more common than clinical mastitis and impossible to detect through observation because subclinical ewes look the same as healthy ewes. The prevalence of subclinical mastitis is at least 15% across flocks and herds while clinical mastitis involves around 3% to 5% of females.

Mastitis of any kind can occur at any time during lactation, although subclinical mastitis is more prevalent shortly after lambing and at weaning.

While it’s easy to find animals with clinical mastitis, detecting subclinical mastitis is more difficult. Bacterial culture is the gold standard test but it’s time consuming and somewhat costly.

Somatic cell count can also diagnose subclinical mastitis. Somatic cells are white blood cells (leukocytes) produced by the immune system in response to inflammatory stimuli. These cells can be counted to determine whether the level indicates infection.

The California Mastitis Test (CMT) can be performed economically on the farm. If the CMT is performed on ewes as they enter the jug, the results can indicate whether it’s worth further testing.

“If she develops subclinical mastitis, it may progress and develop into clinical mastitis,” said Knuth. “In some cases, a subclinically infected ewe or doe may go back to being healthy within a single lactation. However, if a ewe or doe gets clinical mastitis, there is virtually no chance of a cure or going back to being subclinical or healthy. There’s lasting tissue damage associated with clinical mastitis.”

Controlling mastitis can be challenging. Because bacteria are always present in the environment, there’s always risk of infection to the mammary gland, making it impossible to completely eliminate clinical or subclinical mastitis. However, good practices can help producers manage it.

“At lambing or kidding, make sure jugs are cleaned, sanitized and dry before bringing the next set of newborns,” Knuth said. “The cleaner and drier the jug, the less favorable environment for bacteria to grow and reproduce. Cull ewes with poor udder health or poor performance raising lambs or kids.”

If sore mouth is a problem in the flock, mastitis becomes more likely. Lambs and kids with painful sores on their mouths are reluctant to nurse, and females with udder sores will kick away young offspring as they attempt to nurse. The result is udder fill and higher potential for mastitis.

Intrammamary antibiotics commonly used for mastitis in dairy cattle are extra label use in small ruminants, so work with a veterinarian to use these products. Systemic antibiotics such as injectable penicillin may also be beneficial for treatment. Restricting females’ access to water and feed to reduce nutritional intake, especially protein, around weaning also helps manage mastitis.

In herds with a history of mastitis, it’s worth the time to monitor udder health by palpating udders for lumps and scar tissue and examining teats. This can be done during routine handling such as pre-breeding sorting or shearing. When possible, check and treat teats for sores when lambs’ and kids’ teeth are erupting during lactation. Cull ewes and does with clinical mastitis – mammary tissue never fully recovers and females won’t return to full milk production.

Several vaccines are available for mastitis. VIMCO® is approved for dairy and meat goats and targets Staph aureus. Lysigin® for cattle is extra-label use in sheep and goats. A vet may recommend either of these, but it’s important to understand that these vaccines are only effective against limited bacteria types.

by Sally Colby