5 - Brain and lung injury in thoroughbred foals

The Lancet published a letter from Mahaffey and Rossdale (1957) describing their observations on a convulsive syndrome affecting about 2 percent of thoroughbred foals delivered with human assistance.  Their letter was in response to the article by Gunther (1957) on postnatal transfusion and an earlier paper by Bonham Carter et al. (1956) on pulmonary problems and "cerebral irritation" in human infants.

Human-assisted birth

Mahaffey and Rossdale stated, "For a considerable time we have been greatly concerned with the possibility that the syndromes are associated with very early severance of the umbilical cord."  They went on to suggest that this practice may deprive the newborn foal of up to 1500 ml of placental blood, which may be more than 25 percent of a normal foal's blood volume, and then commented:

"It seems more than a coincidence that, as far as we can verify, the syndromes do not occur in thoroughbred foals which are born unattended in open paddocks in Australia, but are well known in France and Italy, where the cord is always severed by attendants within seconds of birth.  Further, in Europe the disease seems to be unkown in breeds of horses other than thoroughbreds and these generally foal without human 'interference.'  Other domestic species which give birth to their young alone, and 'naturally,' are similarly unaffected."

Pulmonary pathology

Mahaffey and Rossdale (1959) described the pulmonary pathology associated with convulsive foal syndrome along with the neonatal behavioral disturbance.  The condition was reported to follow an apparently easy delivery, but when attempting to get to his feet for the first time, the foal begins jerking his head up and down, becomes unsteady on its feet, and falls down.  The animal may emit a barking noise associated with rapid respirations and increased heart rate, then go into violent convulsions.  About half of the foals recover without any apparent residual effects, but may pass through a period of seeming blindness, wandering aimlessly about before learning to suck from their mother.

In foals that died, aeration of the lungs was found to be incomplete.  Lung tissue was described as dark and dense, resembling fetal liver, as opposed to the pink feathery appearance throughout the lungs of foals that did not experience respiratory problems or convulsions in the newborn period.   Abnormalities of lung tissue was noted to be comparable to that described in human infants dying of pulmonary syndrome.  Mahaffey and Rossdale also noted that the ductus arteriosus was patent to a marked degree in the convulsive foals, an indication of incomplete transition to normal postnatal circulation.  They attributed these abnormalities to the conduct of human assisted parturition:

"Variable degrees of traction are usually practised by attendants when the head and forelegs are emerging from the vulva.  The amnion is prematurely ruptured by hand, the legs are grasped and a pull is exerted upon them... the umbilical cord is ruptured with such haste that the newborn foal (weighing 100-120 lb.) is deprived of an average of 1020 ml. of blood and often 1500 ml. -- probably about 30% of its potential blood-volume.

Under normal conditions a mare usually rests for period of up to half an hour after parturition, during which the foal also is inactive.  The cord remains intact and is not broken until the mare (sometimes the foal) attempts to get to its feet.  Meanwhile virtually all the blood in the placenta has passed back into the circulation of the foal, and it is difficult to collect even 50 ml. of blood when the cord ruptures at this stage."

Comparison with pulmonary syndrome in human infants

Dunn (1972) acknowledged the importance of observations on the convulsive foal syndrome for understanding respiratory distress in human infants, which he described as a maladaptation to extrauterine life, most frequently in preterm infants.  He discussed deficiency of surfactant in preterm infants and frequent association with Caesarean section as etiological factors.  The child delivered by Caesarean, "is often born in a state of blue asphyxia -- apnoeic and cyanosed, yet with vigorous cord pulsation...  In most cases the pulsating umbilical cord is clamped at once to allow the obstetrician to complete the operation."  Dunn commented further:

"In fact there is no reason why the cord should be clamped at all and since 1961 I have been advocating and practising delivery of the infant and placenta together as one unit, both being laid together at the same level and the cord only ligated after respiration has been established and all pulsation has ceased.

It is of interest that this practice was widely followed throughout most of the world until the recent spread of Western civilisation.  Even today it is still adhered to in many isolated and primitive communities.   It is of course practised by many animals.

In this context it was with tremendous interest that I read of Mahaffey and Rossdale's (1959) observation that "barkers" were never found among foals born in the open field but only among those delivered indoors with human supervision, including early ligature and division of the umbilical cord."

Cortical and brainstem patterns of damage - as found in monkeys

In 1976 Palmer and Rossdale reported neuropathological changes found in 18 foals that had exhibited signs of the "convulsive foal syndrome."  A spectrum of changes in the brain were observed, including ischemic necrosis within the cerebral cortex in nine of the foals, with involvement of the diencephalon and brainstem in three of these.  Hemorrhagic damage of the cerebrum, and sometimes the brainstem and cerebellum, was observed in the other nine foals.

Palmer and Rossdale compared their findings with the two patterns of damage described by Myers in 1972 seen in monkeys subjected to hypoxia and or asphyxia shortly before or after birth.  Myers subjected monkeys to partial hypoxia late in gestation, which resulted in damage of the cerebral cortex similar to that seen in human cases of cerebral palsy.  On the other hand, when he inflicted catastrophic total asphyxia at birth for several minutes, damage was restricted to the brainstem.  Palmer and Rossdale found brainstem damage in foals who suffered apnea at birth, including lesions of the inferior colliculi as had been the case in monkeys subjected to asphyxia.

From:

http://placentalrespiration.net/

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