HAVING spent the past 11 months getting and then keeping a mare in foal, the last thing any breeder wants to face is a sick, compromised foal after birth.

One of the most severe, and most feared, conditions seen in equine neonates is Perinatal Asphyxia Syndrome (PAS), which is reported to occur in between 1- 2% of all foal births.

The syndrome has had numerous other names over the past few decades, including ‘Hypoxic-Ischemic Encephalopathy (HIE)’ and ‘Neonatal Maladjustment Syndrome.’

More colloquially, the condition is often referred to as ‘Dummy Foal Syndrome,’ with affected foals being branded as ‘dummies,’ ‘wanderers,’ or ‘barkers.’

No matter what name one wants to give it, understanding why it occurs and what a breeder can do to help minimise the risk of it occurring is key to ensure optimal health of all newly born foals on the farm.

Understanding the risk factors

In order to understand how and why things can go wrong, one must have a basic understanding of how things function normally throughout a healthy pregnancy and labour.

The single most important lifeline the unborn foal has is the placenta. This serves as an interface between mare and foal, allowing their circulatory systems to communicate, facilitating passage of vital substances like oxygen and nutrients across it to nourish the the foetus, whilst simultaneously allowing waste products move back across for effective elimination.

The umbilical cord attaches the placenta directly to the foal, and so anything that interferes with either its or the placenta’s function will ultimately be detrimental to the foal’s health.

The exact physiological mechanisms of how a lack of oxygen to a foal’s brain and other organs is so damaging is still not completely understood.

However, it appears the massive inflammatory response that is triggered results in significant cell death, with potentially catastrophic results for the foal.

A number of risk factors associated with the occurrence of Perinatal Asphyxia Syndrome have been identified.

Maternal factors include dystocia (obstructed labour), induced labour, caesarean section, placentitis, premature placental separation (either acute or chronic) and any severe illness or condition which may lead to a lack of oxygen being received by the foetus (endotoxemia, severe respiratory disease, anemia, haemorrhage etc.)

Foetal factors that may predispose to it include twin pregnancies, meconium aspiration, congenital malformations, sepsis, dysmaturity or prematurity and umbilical cord accidents.

Recognising the clinical presentation

Foals affected by PAS may show a wide range of clinical symptoms, ranging from few to many and mild to severe. When the syndrome was first described, it was thought to be predominantly linked with the neurological system, as many foals showed abnormal behaviours such as lacking affinity for the mare, wandering around the stall aimlessly or standing dull in a corner.

Others failed to develop a normal suck reflex, whilst more seriously affected failed ever to rise and were prone to seizure activity.

However, as greater understanding of the condition developed, affected foals often exhibited clinical abnormalities in multiple body systems, with the gastro-intestinal, urinary, cardiovascular and respiratory systems often also implicated.

With this knowledge came the harsh reality of a seemingly endless list of ways affected foals may present including: the onset of severe diarrhoea, being unable to regulate blood pressure and temperature correctly, failing to breathe normally, failing to produce urine etc.

Therapeutic Intervention

Having recognised some of these serious hallmarks of PAS in a foal, it is of monumental importance that veterinary intervention is made without any delay.

In the case of many foals, this often necessitates being admitted to a tertiary level referral hospital where the foal can get 24-hour care under a highly trained team of critical care veterinary staff.

This can involve a whole range of clinical procedures and therapies including intravenous fluid therapy, antimicrobial therapy, anti-inflammatory therapy, total or partial intravenous nutritional feeding, continuous flow-by oxygen supply, blood pressure regulation and monitoring, seizure control and monitoring, etc.

Depending on how severely affected the foal is, how quickly it receives veterinary care, and indeed how many clinical complications it encounters during its treatment will determine the overall outcome.

It cannot be ignored however that PAS is a significant contributor to perinatal death in foals.

Risk Management

As the potential clinical implications of PAS can be life threatening, it is in the interest of every breeder to be aware of the syndrome, what the risk factors are and the symptoms affected foals present.

The most obvious example of this is in mares that have placentitis (inflammation of the placenta).

This occurs most often due to ascending bacteria from the genital tract that traverse the cervix and seed out in the placenta. Such mares often have an abnormal vaginal discharge that is visible from the outside of their vulval lips.

If noted by the breeder, veterinary help can be sought, where both the placenta and the foal can be imaged via ultrasonography, and appropriate treatment instigated to address the placentitis as well as provide on going support to the pregnancy.

Any mares that have a previous history of poor quality placentas, compromised foals, or indeed that have had a significant illness during the course of a pregnancy should be monitored with extra care and ideally should be screened more closely than normal.

If, during ultrasonographic exam a foetus is seen to be under continuous stress for example, it may even be indicated to hospitalise the mare for the end of her pregnancy so that when she gives birth, immediate critical care can be given as needed to maximise chances of survival.

Research is on going to try and understand the syndrome better not only from a physiological point of view, but also devise sensitive diagnostic tests that will indicate affected foals without delay, as well as increasing the arsenal of useful treatment protocols to try and counter-act the numerous detrimental effects.

In the meantime, greater understanding of the condition amongst breeders, coupled with diligent monitoring and input from both first-line and referral level veterinarians will help to maximise good clinical outcomes in as many PAS affected foals as possible.

Sunita Jeawon MVB is a Resident in Equine Internal Medicine at UCD Veterinary Teaching Hospital