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Neonatal maladjustment syndrome (NMS) – also referred to as dummy foal syndrome – is a condition that causes neurological symptoms in foals.
This condition prevents the foal from performing normal behaviours, such as recognizing and feeding from the mare, standing and walking. Affected foals may appear lethargic, depressed, or display more serious clinical signs.
NMS can be caused by oxygen and nutrient deprivation in the foal before birth. It may also be caused by a failure of placental hormones to drop following birth.
NMS affects approximately 1-5% of foals and is primarily found in thoroughbreds. [1][2]
Although dummy foal syndrome is alarming to horse owners, the prognosis is generally good so long as the foal does not have any other health complications.
Neonatal Maladjustment Syndrome
Dummy foal syndrome is also known as neonatal encephalopathy or neonatal maladaptation syndrome.
Foals that have NMS are sometimes referred to as dummies, barkers, convulsives, or wanderers – terms that describe some symptoms of NMS. [3]
Foals diagnosed with NMS are usually divided into two categories: (1) normal at birth; and (2) displaying clinical signs at birth.
Normal at Birth
The first type of foals with NMS are born at term and initially appear healthy and normal. The foal will stand and nurse, but after a few hours will develop abnormal behaviours.
Affected foals will typically no longer recognize their mother (due to vision problems or confusion) and will be unable to suckle from the mare. [4]
Type 1 NMS is often associated with trauma to the chest while the foal passes through the birth canal. [5] The progression of NMS will vary depending on the foal and the specific causative factors.
The foal may wander aimlessly, unaware of his surroundings, or may lose his ability to stand completely. The foal might also flail his legs or may be completely limp.
Severely affected foals are unable to stand and will alternate between having seizures and falling into a coma. The foal’s temperature and heart rate rise during seizures and drop when the foal enters the coma. [6]
If the foal recovers, improved mobility is usually the first noticeable sign of recovery. The foal will learn or re-learn to stand, regain awareness of his surroundings, begin to recognize his mother and his suck reflex will return. [6]
Symptomatic at Birth
Type 2 foals are often born prematurely or experience complications during delivery. Type 2 foals may be underweight at birth and are more likely to have experienced inadequate conditions such as oxygen deprivation, before birth. The foal will begin to show signs of NMS before it is 4 days old, although symptoms are usually present immediately at birth. [5]
Healthy foals typically stand within an hour of birth and begin to drink from the mare within 2 hours of birth. [7]
Foals born with NMS usually will not stand and will have no suckle reflex, which prevents them from drinking from the mare or even a bottle. The foal will be very weak and will likely develop sepsis. Type 2 foals are prone to the same symptoms as type 1 foals, and their recoveries follow the same sequence.
Signs
Foals that develop NMS will usually show a number of the following symptoms, which may come and go or may change as the condition progresses: [1][6][8]
- Seizures
- Tremors (shaking) in head and neck
- Weakness or lethargy
- Blindness
- Staggering
- Legs splayed; difficulty standing
- Stiff legs
- Disinterest in the mare or lack of recognition of the mare
- Loss of suck reflex
- Walking into things (due to blindness or lack of awareness)
- Recumbency
- Flailing legs while recumbent
- Restlessness or over-excitement
- Intermittent coma
- Jaw champing or grinding teeth
- Excessive saliva
- Excessive licking
- Tongue protruding out of mouth
- Abnormal breathing or gasping for air
- Vocalizations that sound like barking (often due to broken ribs)
- Sweating
- Constant ear flicking
- Constant blinking
The affected foal might also experience the following health complications: [1][4][6][9][10]
- Lesions on liver and/or kidney
- Colic
- Stomach ulcers
- Ileus – decreased digestion caused by reduced intestinal muscle contraction
- Necrotising enterocolitis – intestines become inflamed and begin to die
- Retained meconium – foal cannot pass its first feces and becomes impacted
- Weakened heart
- Low or elevated heart rate and blood pressure
- Collapsed lung
- Sepsis
- Kidney damage resulting in less urine production
- Acidosis (blood pH below 7.3 and low bicarbonate concentration in the blood), leading to organ and brain damage
- High red and white blood cell counts
- Congestion in the lungs
- High blood CO2
NMS may last anywhere from several hours up to approximately 30 days. [6]
Prognosis
The prognosis for foals that are asymptomatic at birth is good, with approximately an 80-87% survival rate. [8]
Foals that are symptomatic at birth were reported to have a survival rate of less than 50% in a 1996 study. [5] However, improved understanding and treatment of dummy foal syndrome may have resulted in higher survival rates since then.
Long-term neurological side effects of meonatal maladjustment syndrome in horses are rare.
Causes
NMS may be caused by hypoxic ischemia in which oxygen and nutrient deprivation cause the foal to display abnormal neurological symptoms.
NMS may also be caused by a failure of placental hormones to drop to normal levels in the foal after birth. [11]
Hypoxic Ischemia
NMS is sometimes called perinatal asphyxia syndrome or hypoxic-ischaemic encephalopathy because the foal may experience hypoxia and ischemia. [9]
Hypoxia describes a situation in which there is insufficient oxygen in tissues or the blood.
Ischemia refers to impaired blood flow to organs or tissues, interfering with oxygen and nutrient delivery.
Hypoxia and ischemia deprive the foal’s brain of oxygen and cause neurological damage, such as:
- Lesions on the brain, spinal cord, and lungs
- Cerebral oedema (fluid in the brain)
- Brain bleeding
- Neuronal death (death of neuron cells)
Neurons are the cells that communicate signals in the nervous system. These cells are responsible for sensing stimuli, determining how to respond, and relaying messages to the muscles. [9]
Symptoms will vary depending on the severity of oxygen and nutrient deprivation. [10] Hypoxic ischemia can also affect other organs. [9][10]
Causes of Hypoxia and Ischemia
Hypoxia and ischemia in foals can be caused by several different condition before, during, or after the foal is born, including: [4][6][10][13]
- Respiratory disease
- Endotoxemia (bacteria causing systemic inflammation in the mare)
- Surgical delivery of the foal
- Anemia
- Placentitis
- Separation of the placenta from the endometrium (the inner lining of the mare’s uterus), inhibiting blood delivery
- Presence of twins
- Fetal congenital defects
- Dystocia (mare struggles to deliver the foal because of large foal size or because the fetus is in an irregular position in the uterus)
- Sepsis (infection reaching the fetus’ blood causing inflammation, damage to multiple organs, and potentially lowered blood-flow to organs)
- Fetal infection
- Extreme pressure to the foal’s chest while passing through the mare’s pelvis during delivery, impacting the foals heart and lungs and disrupting circulation
- Umbilical cord being cut too early
Premature cutting of the umbilical cord is one of the most common causes of dummy foal syndrome. [1] Cutting the cord too early prevents all of the blood from passing from the placenta to the fetus, depriving the foal of up to one-third of its blood volume.
Failure of Placental Hormones to Drop
Before birth, several factors keep the foal unconscious in the mare’s uterus and inhibit the foal’s central nervous system from functioning: [11][12]
- Low levels of oxygen in the fetus’s blood
- High levels of pregnancy hormone supplied by the placenta
- The warmth and pressure of the uterus
After birth, the supply of placental hormones is cut off and most hormone levels drop significantly before the foal is two days old.
Declining hormone levels, higher blood oxygen as the foal breathes on its own, and exposure to the external environment cause the foal to gain consciousness.
This is important so that the foal can perform activities necessary for survival, such as learning to stand, walk, and nurse. [11]