The Maladjusted Foal
The Frank J. Milne Lecture at the Denver AAEP Convention was presented by Peter Rossdale, OBE, MA, PhD, Dr. (h.c.) Berne, Dr. (h.c.) Edinburgh, DESM, FACVSc, FRCVS. The title of his talk was "The Maladjusted Foal: Influences of Intrauterine Growth Retardation and Birth Trauma."
Rossdale's primary area of research is equine reproduction, and he has won numerous awards and honors for his work in this field. He is past president of the British Equine Veterinary Association and has served as editor of Equine Veterinary Journal since 1980 and as editor-in-chief of Equine Veterinary Education since 1991. He has published more than 160 scientific papers in numerous research journals. Assisting in one part of the presentation was Paul Sibbons, PhD, deputy director of Northwick Park Institute for Medical Research.
The Milne Lecture is named for the late Frank J. Milne, past president and distinguished life member of AAEP. Debuting at the 1997 convention, the Milne Lecture focuses on subjects and techniques considered "state of the art" by the equine veterinary profession.
The basic theme of Rossdale's presentation was that problems suffered by the fetus before birth and during the birthing process can have long-term effects on the animal's performance capability and overall health as it grows and matures. With that as a premise, he identified and discussed some of the factors that can have a negative effect before the foal is born and during birth.
First, he acquainted his listeners with two terms that were used with some frequency during the presentation. A disturbance of normal fetal development, Rossdale said, has been identified with the term intrauterine growth retardation (IUGR). The term dysmaturity, he said, was coined to describe signs of immediate post-natal maladjustment and weakness in foals that had been carried at least 320 days but that mirrored clinical signs of premature foals.
The term IUGR, as well as placental deprivation, denotes clinical signs of malnourishment and physiological deficits inherent in those individuals born after a gestation involving interference with normal placental transfer of metabolites and nutritional requirements in utero, he said.
"Fetal growth and development depends on the intrauterine environment responsible for supplying nutritional, metabolic, and endocrine requirements, he said. The majority of these needs are derived directly or indirectly from the maternal source. Fetal growth retardation has been defined as a condition of pregnancy in which the developing fetus undergoes a pathological process modifying its growth potential by reducing its growth rate. Recently, the term IUGR has also been used to include reduced cellular structure and function."
The fetus is being biologically programmed for future life, Rossdale further explained, but fetal growth and development is dependent on the metabolic, nutritional, and hormonal environment provided by the dam and programming for the future might be modified by any disturbance in that relationship.
Rossdale said there is a pathway of supply and demand between the fetus and the mare, and this pathway moves through the umbilical vein into the fetal circulation.
"The system is completed through the umbilical arteries," he said, "enabling exchanges between fetal and maternal pathways to occur in the reverse direction. Any disturbances in these pathways to or from the fetus may modify fetal development. These modifications can range from severe and immediate effects, evidenced by abortion or neonatal maladjustment, to more subtle long-term deficits that may not become clinically apparent until later in life.
"In summary, an adverse fetal environment may impose substantial limits on future health and athletic performance of the horse," said Rossdale.
Key to proper development of the fetus is appropriate nutrition, Rossdale said. Recent studies indicate that malnutrition can bring with it a host of problems for the fetus, including inappropriate hormone levels.
"Nutritional availability in utero is a major influence on circulating levels of hormones, such as insulin, thyroxine, cortisol, prostaglandins, and growth factors which, in turn, regulate the uptake and metabolism of nutrients by the fetus," Rossdale told his listeners. "Nutrient availability also regulates the duration of pregnancy in any given individual. When nutrient availability is limited, fetal concentrations of insulin and thyroxine fall, whereas concentrations of prostaglandins and cortisol rise.
"Therefore, changes in endocrine status of a fetus may have profound significance on body growth and microstructural elements of specific organ systems in individuals affected by disturbances at the placental/endometrial level," he explained.
The invasion of infectious agents also can compromise the fetus, he said. "Important external environmental influences associated with abortion include infectious agents such as herpesvirus, arteritis, and leptospirosis, whereas bacterial and fungal infections may, in association with placental pathology, result in IUGR.
"The ingestion of noxious substances, such as tall fescue endophyte, presents definitive risks, as well as the administration of drugs," he added.
When IUGR is involved, Rossdale said, the range of possible effects on the animal as a neonate, and later as an older horse can be:
- Pulmonary failure in the newborn, resulting in atelectasis (failure of a lung to properly expand) and respiratory distress, particularly on the second and third day after birth.
- Failure of the foal to establish an immediate post-natal respiratory rhythm.
- Disturbances within the breathing apparatus that can predispose the horse to exercise-induced pulmonary hemorrhage (EIPH) later in life.
- Pathological changes in the nervous system that can involve idiopathic (of unknown cause) laryngeal hemiplegia and problems with laryngeal muscles.
- Other conditions, including hyperlipemia (elevated level of triglycerides, or storage fats), chronic obstructive pulmonary disease (COPD), osteochondrosis, and muscle diseases.
From Fetus to Athlete
Rossdale said there are strong indications that uterine environment plays a major role in the type of athlete a horse turns out to be. Some researchers have emphasized that fetal growth and development are controlled by genetic factors determined by the fetal genome and environmental factors, such as maternal nutrition, that alter the expression of the fetal genome.
"This concept may be applied to horses, particularly with respect to the narrow genetic base of Thoroughbreds, whose linearity stems from only 30 founders, 27 of these being male. With a narrow genetic base in the population, it might be expected that performance would have correspondingly narrow presentation. However, this is not the case, which suggests that the environment in utero may play a significant role in influencing the athletic expression of the genome," said Rossdale.
In the United Kingdom, Rossdale said, between 50-60% of Thoroughbreds do not reach the racetrack. Those that do reach the track on average race twice as two-year-olds and three times as three-year-olds. Many of the problems afflicting these horses are musculoskeletal in nature, and many of them are traceable to a compromised environment within the uterus before the foal was born, he indicated.
Signs of Fetal Compromise
The good news involving IUGR is that the mare owner and veterinarian can be alerted to potential problems by outward signs and sophisticated technology.
Rossdale said indirect evidence that can signal possible fetal compromise includes the following:
- External signs of vaginal discharge might be seen at the vulval labia and/or on the perineum or hocks of the mare. Vaginal inspection might show a moist, relaxed cervix and exudate emerging, or inflammation of the vagina.
- Early enlargement of the mammary glands and secretion or dripping of milk.
- Maternal behavior patterns that denote abdominal pains, such as uneasiness, patchy sweating, or lack of appetite.
- Signs of disturbance based on fetal heart rate, determined with ultrasound. (Recent research involved assessing pregnancies in individuals with suspected problems during the period of 298 days to full term and included a profile of well-being based on six parameters--fetal heart rate, aortic diameter, maximal fluid depth, utero-placental contact, utero-placental thickness, and fetal activity, said Rossdale. A low score was a definite indicator that problems existed, but a high score was less reliable as to ultimate outcome.)
- Measurement of maternal jugular blood endocrine levels and mammary secretions.
Realizing there have been in-utero problems does not mean that conditions can be changed so that a normal, healthy foal is delivered. However, the knowledge does allow the veterinarian and horse owner to be prepared for handling the compromised foal when it is delivered, Rossdale said. It also enables the veterinarian to take steps to prevent premature foaling.
Rossdale then turned to problems that can occur during birth and adaptation by the foal to its new environment outside the uterus.
The birthing process is a normal event involved in propagation of the species, but management by man, in some instances, has had a negative influence, he told his listeners. He listed the breeding of Thoroughbreds as an example. These horses are bred to run and little attention is paid to breeding for proper birth size, he said. As a result, a number of Thoroughbred foals--as many as 20%--suffer fractured ribs while making their way through birth canals that are too small for their bodies.
Once the newborn foal is delivered it must go through dramatic changes in adapting to life outside the uterus. To adapt or adjust to the changed demands, a series of corresponding alterations occur. They include:
- The division of the circulation into left and right channels through the body and lungs respectively.
- The establishment of pulmonary (lung) function with its corresponding increase in oxygen supply and utilization within tissues.
- The activation of reflexes to sustain sucking, alimentation (absorbing nutrients), defecation, and the ability to stand and nurse, as well as bond with its dam.
- The establishment of systems needed to maintain body temperature and metabolic balance.
"The key to successful management of conditions of the neonate," Rossdale said, "is early recognition of the clinical signs."
Because the foal's organs are very unstable at birth, the youngster is vulnerable to rapid deterioration and mortality, thus the need for instant action if problems are present, he said.
"The important consideration is the criteria of normality as interpreted from the clinical viewpoint," said Rossdale. "Behavioral patterns are the basic judgment of normality, and the first episodes of standing and sucking from the mare represent objective determinants. The clinical parameters of circulatory and thermostability are based on pulse and respiration rates.
"The manner of defecation, volume of urinary output, and normality of these excretions are clinical indicators of health or incipient signs of problems developing in the neonatal foal," he added.
"Assessment of respiratory status is perhaps the most important single tool in evaluating the normality of an individual's adaptive capacity," he noted. During the first three to 10 minutes after birth, the foal will breathe at the rate of about 70 breaths per minute. This will drop to 35 breaths per minute in about one hour and will remain at that rate for at least the first 48 hours, providing the foal is at rest.
Research has shown that a foal's heart rate will stabilize at about 106 beats per minute beginning with one day of age and will remain at that rate for about two months, when it will drop to about 77 beats per minute, said Rossdale. However, from six to 60 minutes of age, the foal's heart rate is about 129 beats per minute; from nine to 48 hours, it is normally 95 beats per minute.
If the foal's heart rate immediately after birth is 40 beats per minute or less, he said, it is an indication that there was a lack of oxygen available to the foal during the birthing process. After six hours post-birth, a heart rate of more than 120 beats per minute may indicate anemia, thoracic (chest) damage, or congenital cardiac conditions.
Rossdale then shared with his audience some case studies involving maladjusted foals. Some survived; others did not. In almost all instances, the prime organ adversely affected was the lung.
"In the horse, the lungs seem to be the organ most affected by perturbation in the process of achieving fetal maturity (problems within the uterus), and therefore, with the most potential to limit chances of survival in the post-natal adaptive period," concluded Rossdale.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
POLL: University Equine Hospitals