How to Anesthetize Foals on the Farm for Minor Surgical Procedures

1. Introduction
There are many situations in which it is necessary to anesthetize foals on the farm or in the field. Periosteal transaction, umbilical hernia repair, transphyseal screw removal, regional perfusion, and joint lavage are a few instances in which general anesthesia is preferred over sedation. It is important for the practitioner to understand the drugs available for general anesthesia and the potentially detrimental effects that can occur when dealing with an immature metabolic and cardiovascular system. Although many anesthetic protocols are available, finding a relatively simple and safe protocol in which the practitioner is familiar will minimize risk associated with anesthesia. The following is an example of a protocol that is successful in a private practice in Lexington, Kentucky.

2. Neonates Versus Foals
The definition of a neonate is typically a foal <1 wk of age; however, this definition can include foals up to 1 mo of age, particularly when the foal is sick. The definition is important, because there are physiologic variations in neonates that alter the way in which drugs are redistributed and metabolized as well as variations in the cardiovascular system. An elevated metabolic rate, immature hepatic and renal function, lower body fat, and increased risk of hypotension and hypothermia are a few of the concerns associated with neonates.¹  Additionally, cardiac output is dependent on heart rate and stroke volume. Drugs that slow the heart rate, such as the alpha-2 adrenergic agonists like xylazine, can significantly alter cardiac output, because neonates have a decreased capacity to increase stroke volume to compensate.² [...]