Contagious Agalactia in Sheep: Mycoplasma Disease of Milk, Eyes, and Joints

Contagious agalactia is a highly contagious bacterial disease of sheep caused most often by Mycoplasma agalactiae. It is best known for causing mastitis, eye inflammation, and arthritis, although not every sheep shows all three problems. In lactating ewes, one of the first clues may be a sudden drop in milk production or milk that looks watery, clotted, yellow, or grainy.

The disease matters because it can spread through a flock, reduce milk yield, affect lamb growth, and leave some animals as long-term carriers. In chronic cases, the udder may shrink after damage to milk-producing tissue. Some sheep mainly show lameness or pinkeye instead of udder changes, which can make the condition easy to miss early on.

This disease is not considered zoonotic, so it is not known to be a human health risk. Still, it is a serious flock health issue and should be handled with strong hygiene and isolation steps while your vet guides testing and next decisions.

In sheep, contagious agalactia is caused mainly by Mycoplasma agalactiae, a bacterium without a typical cell wall. Other Mycoplasma species can cause a similar syndrome, especially in goats, but M. agalactiae is the main concern in sheep. Because Mycoplasma infections can persist and some animals become carriers, the disease may stay in a flock for a long time if it is not recognized and managed carefully.

Spread happens through infected milk, close contact, contaminated milking equipment, secretions from the eyes or nose, and movement of carrier animals into the flock. Lambs can become infected through colostrum or milk from affected ewes. Outbreak risk often rises around lambing and milking, when animals are in closer contact and udders are under more stress.

Flock introduction is a major risk factor. New sheep, returning show animals, and contact with goats or neighboring small ruminants can all increase exposure risk. Shared equipment, poor sanitation, and inadequate isolation practices can also help the organism move from one animal to another.

Diagnosis starts with your vet looking at the pattern of disease in the flock. A ewe with mastitis, pinkeye, or swollen joints may raise suspicion, but contagious agalactia cannot be confirmed by signs alone. Other causes of mastitis, infectious keratoconjunctivitis, lameness, and joint infection can look similar.

Definitive diagnosis usually depends on laboratory testing, especially PCR, culture, or both. Useful samples may include milk, conjunctival swabs, ear swabs, and joint fluid. In dairy settings, bulk tank milk can sometimes help monitor the flock. Serology may be used in some unvaccinated flocks, but it can be less helpful in chronic infection and usually does not replace direct organism testing.

Because chronic carriers can be hard to identify, your vet may recommend testing more than one animal and repeating samples if early results are unclear. A flock-level plan often matters as much as the diagnosis in one ewe, especially when milk loss, lamb growth, or multiple clinical signs are affecting production.

Prevention focuses on biosecurity, isolation, and careful flock additions. Any sheep with suspicious udder changes, pinkeye, or lameness should be separated from the healthy flock right away. New arrivals should be isolated before mixing, and many sheep biosecurity programs recommend at least 30 days, with longer separation often preferred when health history is uncertain. Avoid nose-to-nose contact during quarantine.

Milking hygiene matters. Clean and disinfect milking equipment, handle affected ewes last, and avoid sharing contaminated tools between groups. Good sanitation in lambing and milking areas can reduce spread through secretions and milk. If goats are present on the farm, discuss cross-species risk with your vet because mixed small-ruminant operations can complicate disease control.

Work with your vet on a flock health plan that covers testing of suspect animals, purchase policies, visitor and equipment control, and response steps if a case appears. Vaccines are used in some parts of the world, but protection is variable, and vaccination during an active outbreak is generally not recommended. In many flocks, the most practical prevention tools are closed-flock practices, quarantine, testing, and fast isolation of suspect animals.