AAEP Convention 2004 Wrap-Up: Milne Lecture (Foals)
The Frank J. Milne Lecture 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 many awards and honors for his work in this field. He is a 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 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 theme of Rossdale's presentation was that problems suffered by the fetus before and during birth 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 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.
"Any disturbances in these pathways to or from the fetus may modify fetal development," he stated. "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 abnormal hormone levels.
"Nutritional availability in utero is a major influence on circulating levels of hormones, such as insulin, thyroxine, cortisol, prostaglandins, and growth factors that, in turn, regulate the uptake and metabolism of nutrients by the fetus," Rossdale said. "Nutrient availability also regulates the duration of pregnancy in any given individual.
"Therefore, changes in endocrine (hormone) 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, he said, the range of possible effects on the animal as a neonate and later as an older horse can be:
- Pulmonary failure 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 the 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, he 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.
He said indirect evidence that can signal possible fetal compromise includes:
- 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.
- 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 to handle a compromised foal when it is delivered, Rossdale said. It also enables the veterinarian to take steps to prevent premature foaling.
He then discussed problems that can occur during birth and adaptation by the foal to its environment outside the uterus.
Man's management of birthing, in some instances, has had a negative influence, he began. He listed the breeding of Thoroughbreds as an example, saying that these horses are bred to run and little attention is paid to breeding for proper birth size. 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.
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 circulation 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 neonate," 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 (bpm) beginning 43 hours post-partum and will remain at that rate for about two months, when it will drop to about 77 bpm, said Rossdale. However, from six to 60 minutes of age, the foal's heart rate is about 129 bpm; from nine to 43 hours, it is normally 95 bpm.
If the foal's heart rate immediately after birth is 40 bpm or less, he said, it means there was a lack of oxygen available to the foal during birthing. After six hours post-birth, a heart rate of more than 120 bpm may indicate anemia, thoracic (chest) damage, or congenital cardiac conditions.
"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.
More information: www.TheHorse.com/ViewArticle.aspx?id=5404.
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.
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