Placentitis is the term used to describe a condition of inflammation and infection of the mare’s placenta. It alters blood supply to the developing foetus which may lead to delivery of under-developed, premature and septic foals or at worst, abortion of the foal. Placentitis is the most common cause of placental abnormality and a leading cause of pregnancy loss in the mare. The cause is almost always an ascending infection that enters the uterus via the cervix. Common bacteria implicated are Streptococcus, Klebsiella, E.coli and Pseudomonas. Fungal infection is also possible. Placentitis is often insidious in nature and clinical signs may not become apparent until the disease is well progressed, making effective treatment more difficult. Any mare can be affected, but typically affected mares are middle aged, have had foals before, may have poor conformation of the reproductive tract and may have a history of previous episodes of placentitis.

  • Clinical Signs

The most common presenting sign is premature development of the udder and lactation. Vulvar discharge is an inconsistent finding, and whilst it is often present in affected mares, it may be so subtle as to be unnoticed. Close examination of the tail hairs is advisable for this reason.

  • Diagnosis

Transrectal and transabdominal ultrasound are both useful for investigating placentitis. Using the rectal probe, the attending veterinarian will seek to identify the combined thickness of the uterus and placenta (CTUP). This is a standardised procedure for which there are established normal values for the CTUP at various stages of pregnancy. Placentitis has been shown to cause a pronounced increase in CTUP, but it is to be noted that a normal measurement does not preclude the existence of placentitis. Placental separation, if present, is strongly indicative of an ascending placental infection and overrules any measurements taken. Transabdominal ultrasound is used to assess foetal wellbeing, including heart rate, activity and size. An assessment of the other fluid components of the placenta can also be made. Speculum examination of mares with discharge usually reveals it to be originating from the cervix. The cervix can be swabbed to determine the causative agent and determine the most suitable antibiotic. Additionally, the veterinarian may elect to sample the mare’s blood levels of progesterone and oestrogen to further assess the health of the foeto-placental unit. Mammary electrolytes can be used to predict how close the mare is to foaling.

  • Treatment

The treatment for placentitis is primarily aimed at controlling infection and reducing inflammation. In the absence of, or while waiting for, culture and sensitivity results, broad spectrum antibiotic treatment should be started (e.g. trimethoprim sulphonamides). Cases of fungal placentitis are more complex and require a slightly different approach. Progestins (e.g. altrenogest – trade names including Regumate, Ovumate) are advocated to relax the uterus and avoid abortion. Non-steroidal anti-inflammatory medication (e.g. flunixin, bute) are indicated to reduce inflammation. Aspirin has also been used in some mares, owing to its ability to improve uterine blood flow.

Mares should be monitored closely throughout the remainder of their gestation. In advanced cases, where placental separation has already occurred, treatment is often unrewarding, and it is not uncommon to encounter abortion, stillbirth or the preterm delivery of a severely compromised premature foal. Any foal born to a mare with placentitis (premature or not) should be treated as being at a high risk of sepsis and managed accordingly. The mare must also be considered at high risk of recurrence in subsequent pregnancies and managed with regular ultrasound scanning and targeted treatment. Such mares are usually examined at 120-150 days of pregnancy and then re-examined on a monthly or fortnightly basis as necessary until foaling. .Perineal conformation must be critically assessed and a Caslick’s procedure performed if there is any doubt.

  • Prognosis

If the condition is diagnosed early and aggressive treatment initiated with a combination of broad spectrum antibiotics, altrenogest and non-steroidal anti-inflammatory medication, up to 73% of mares may deliver live foals.