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Contagious agalactia
Contagious agalactia is one of the main diseases of dairy sheep and goat farms around the Mediterranean, Tunisia and the Maghreb included. It is caused by bacteria from the mycoplasma group, micro-organisms that are tiny and fragile on the...
What is it?
Contagious agalactia is one of the main diseases of dairy sheep and goat farms around the Mediterranean, Tunisia and the Maghreb included.
It is caused by bacteria from the mycoplasma group, micro-organisms that are tiny and fragile on the outside, but which are transmitted very well from one animal to another in a herd.
Its name comes from the most significant sign: the fall, sometimes sudden and definitive, in milk production.
Key point
Economically major disease of small ruminant dairy farms in the Mediterranean region. An unexplained loss of milk in several females should always make us think of it.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Rapid drop in milk production, until one or both quarters of the udder completely dry up.
Modified milk: lighter, lumpy, yellowish, sometimes frankly altered.
Hot, swollen and painful udder at first, then hard and atrophied: the area will no longer produce milk.
Fever and depression in the acute phase, decreased appetite.
Swollen and painful joints, especially in the limbs: the female limps, hesitates to move, remains lying down.
Eye damage: redness, tearing, eye becomes whitish; some animals lose their sight, sometimes reversibly.
Abortions among some pregnant females.
In young people: arthritis, eye damage, possible mortality.
In herds affected for a long time, the disease takes hold in a discreet form, with carrier animals without apparent signs contaminating others with each birth.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
The disease is caused by mycoplasmas, of which Mycoplasma agalactiae is the main representative in sheep. Other species of mycoplasma give a similar picture in goats.
These bacteria colonize the udder, joints and eyes after passing into the blood.
Apparently cured animals remain carriers and excrete the bacteria intermittently, particularly in the milk, for many months: they are the ones who maintain the disease in the herd.
Dairy farming of sheep and goats, in particular with poorly adjusted or poorly disinfected mechanical milking.
Purchases of animals without quarantine or known health status.
Mixing of herds on the rangelands, transhumance, markets and gatherings.
Group farrowings in overcrowded premises.
Breastfeeding young people with mixed raw milk, which spreads the bacteria to an entire generation.
Insufficient milking hygiene: no disinfection of teats, same linen for all females.
Transmission
Through milk: from the mother to the suckling young, and from one female to the other through the milking machine or the hands of the milker.
By direct contact between animals, through ocular and nasal secretions.
By the environment and the equipment: litter, headrails, milking cups, milking linen used from one female to another.
By the introduction of purchased carrier animals without visible signs: this is the most common method of entry into a healthy herd.
Passage through colostrum and raw milk contaminates lambs and kids very early.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian examines the udder quarter by quarter, the joints and the eyes, and takes stock of the herd's milk curve.
The definitive diagnosis requires the laboratory: analysis of milk, joint fluid or eye secretions, direct search for the bacteria or blood analysis for antibodies.
It is important to take these samples before any antibiotic treatment, otherwise the results will be uninterpretable.
The reasoning is done at the scale of the herd, not just the animal presented: the veterinarian looks at how many females are affected and where the disease entered.
Treatment
Treatment is based on antibiotics active on mycoplasmas, prescribed and monitored by the veterinarian. The families usually used are tetracyclines and macrolides; Not all families of antibiotics are effective against these particular bacteria.
Early treatment significantly improves the chances of saving milk production; started late, it calms the infection without returning the lost milk.
Anti-inflammatories are useful in very painful animals, especially in cases of arthritis.
An essential point to understand: the treatment does not always rid the animal of the bacteria. Treated females remain carriers and contaminating.
Affected animals must be isolated and treated last, using disinfected equipment afterwards.
The waiting periods for milk and meat must be scrupulously respected: your veterinarian will tell you these.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Only introduce animals from herds with known status, and respect a quarantine before any mixing.
Take care of milking hygiene: clean hands or gloves, disinfection of teats, one cloth per female, cleaning and disinfection of the milking machine, regular maintenance and adjustment.
Milk sick or suspicious females last.
Avoid mixing raw milk for breastfeeding young people; colostrum from an affected mother should not be distributed to others.
Quickly isolate any female that is losing milk, limping or has a bad eye, and call the veterinarian.
Culling chronic carrier females, who maintain contamination year after year.
Clean and disinfect the premises, particularly before the farrowing period.
Vaccination
Vaccines exist and are used in several countries in the Mediterranean basin. They reduce the frequency and severity of cases, without guaranteeing total protection or eliminating carriage.
Their availability and their interest depend on the strains present locally: it is the veterinarian, who knows the situation in your region and your herd, who judges their usefulness and the schedule.
Vaccination never replaces milking hygiene and purchasing control: it is complementary.
Possible complications
Permanent loss of one or both quarters of the udder: the female will no longer produce milk, which most often leads to culling.
Permanent blindness in some of the animals affected in the eyes.
Chronic arthritis with persistent lameness and weight loss.
Abortions and sickly young people.
Mortality in prematurely affected lambs and kids.
Long-term establishment of the disease in the herd, with relapses at each calving period.
When to see a veterinarian
Many females lose their milk in a short time or give lumpy milk.
An udder is hot, hard and painful.
Animals limp with swollen joints.
Red, watery or whitish eyes appear in many animals.
Abortions occur in the herd: never consider them trivial, have them analyzed.
Lambs or kids die with swollen joints.
Prognosis
The prognosis depends greatly on the precocity of treatment.
Treated early, some females recover part of their production; treated late, most permanently lose the affected quarter(s).
Mortality remains low in adults, but the economic impact is heavy: milk lost throughout the lactation, anticipated reforms, young people penalized.
At the herd level, sanitation is fundamental work, which is based on milking hygiene, purchasing control and the elimination of chronic carriers.
Frequently asked questions
My ewe lost her milk on only one side: is this permanent?
It's possible. When the quarter becomes hard and atrophied, it generally no longer produces milk. This is why you should call the veterinarian as soon as production drops, and not wait to see.
Is the milk of affected females dangerous?
It should not be consumed or given to young people: it contains the bacteria and spreads the disease to the entire next generation. Raw milk is never recommended in any case, and waiting times after treatment must be respected.
Can a cured female infect others?
Yes. Animals that have returned to normal appearance continue to excrete the bacteria intermittently, especially through milk. This silent carriage explains the herd's relapses each calving season.
How did the disease get into me?
Most often by a purchased animal, carrying it without any visible signs. Then come the mixing on the routes, the gatherings and the shared milking equipment. Quarantine upon purchase is the most profitable measure.
References
WOAH — Organisation mondiale de la santé animale (ex-OIE)
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
Content reviewed by the TunisieVet editorial team · Updated 09 August 2026
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