Modern concepts of neonatal disease in foals.

The article discusses the health issues in newborn foals (baby horses) relating to neurological, biochemical, and cardiopulmonary dysfunctions, and potential infections due to the absence of initial immunity. It categorizes neonatal conditions into four groups: infective, non-infective, developmental abnormalities, and immunological conditions, and highlights prenatal factors responsible for the adverse health conditions.

Classification of Neonatal Conditions

• The paper categorizes neonatal equine disease into four groups based on observed symptoms and potential causes. These are:
  • Infective conditions: This includes illnesses characterized by symptoms such as fever, lethargy, and weaker suck reflex in foals.
  • Non-infective conditions: These conditions are often characterized by major behavioral disturbances in the foal, but are not caused by infection.
  • Developmental abnormalities: This refers to issues related to the physical development of the foal.
  • Immunological conditions: These are conditions arising due to reactions between the maternal and fetal tissues, indicating issues within the immune system.

Foetal and Birth Stress

• The research points out that many neonatal conditions often originated pre-birth, as several intrinsic and extrinsic factors can potentially interfere with normal fetal development. The term “stress” refers to abnormal changes in the fetal environment.
• Stress can be particularly detrimental during gestation, leading to acute or chronic influences on fetal stability. Early gestation acute stress can result in fetal death, while its occurrence in late gestation could lead to stillbirth or severe behavioral abnormalities.

Causes of Foetal Stress

• During birth, the process moves from relying on placental to pulmonary respiration, inducing a certain degree of asphyxia in the foetus. This causes low systemic and cord arterial blood pH levels, and high lactic acid content.
• Abnormal birth circumstances, such as cord compression or placental hypofunction, can further exacerbate the stress, pushing arterial blood pH and lactic acid levels beyond the normal range and interfering with cardiopulmonary function.
• Foetal stress during birth can also be linked with infection agents that reduce the placental efficiency. This can lead to hypoxia and fetal malnutrition which might cause disturbances in blood flow through the uterus or placenta.

Stress as a cause of Neonatal Conditions

• Stress can potentially interfere with the adaptive processes in foals. For example, placental infection (placentitis) can result in fetal hypoxia and malnutrition, reducing cardiac glycogen reserves and subsequently affecting the circulatory system’s adaptation in neonatal horses.
• If the stress experienced during foetal birth goes beyond critical levels, it may lead to pulmonary hypertension, cardiac issues, and failure of pulmonary function, thereby causing further hypoxia.

Extrinsic Factors

• The extrauterine environment – outside the womb – contains several factors from which the fetus is protected while in utero. These include micro-organisms, low temperatures, and gravity effects.
• Adjusting to these conditions requires increased energy from the newborn, and failure to adapt can lead to further health problems.