Anesthesia for neonatal foals

Early castration in foals: Consequences on physical and behavioural development

BACKGROUND

The impact of very early castration of foals has not yet been studied despite the many positive effects observed in dogs and cats.

OBJECTIVES

The objective of the study was to compare castration at 3 days and 18 months and assess their subsequent morphological and behavioural development.

STUDY DESIGN

This was a randomised, blinded clinical study.

METHODS

Twenty-two Welsh ponies underwent either early (3-day old, EC group, n = 11) or traditional (18-month old, TC group, n = 11) castration. Animals were followed up to 3 years of age. All ponies were castrated using a primary closure technique under general anaesthesia. Weight and morphometric measurements were monitored monthly from birth until 8 months of age in both groups. Then, measurements were taken every 3 months until 2 years of age and then every 6 months until 3 years of age. Temperament tests were performed on all animals when they were 1- and 3-years old.

RESULTS

No differences were observed between the EC and TC groups in terms of physical development from birth until 40 months of age or in terms of temperament and behaviour at either 1 or 3 years of age.

MAIN LIMITATIONS

The study included only one breed (Welsh ponies) and only 22 animals that were castrated before 2 years of age, precluding comparison with castration performed at older ages.

CONCLUSIONS

We demonstrate that early castration at 3 days does not interfere with morphological or behavioural development.

Physiologic and pathophysiologic considerations for ruminant and swine anesthesia

This article presents physiologic and pathophysiologic processes that may affect decisions regarding anesthetic protocol. Various organ systems are discussed with specific attention given to pathophysiologic alterations and their effects on anesthesia.

Anesthesia and sedation of foals

Physiologic similarities and differences between foals and adult horses, including response to pain, cardiopulmonary function, ability to compensate for dehydration and hemorrhage, and response to anesthetic drugs, are considered in this article. Preanesthetic evaluation, choice of anesthetic drugs, technique, and monitoring support requirements through to anesthetic recovery are based on these physiologic considerations. Anesthetic techniques discussed include drugs for premedication, parenteral or inhalational anesthetic induction, and maintenance using inhalational and parenteral anesthesia. Where possible, the cardiopulmonary response of foals to individual anesthetic drugs or a combination of them is provided.

Management of anesthesia in the foal

Several unique pharmacologic and physiologic factors must be considered when attempting to anesthetize premature or neonatal foals. Juvenile foals are similar to adults in their physiology and metabolism. Anesthetic drug and protocol selection should reflect the differences between these two age groups. Neonates are best anesthetized using an inhalation technique, whereas older foals can be safely anesthetized with either parenteral or inhalation anesthetic agents. Careful monitoring is absolutely essential when anesthetizing foals. The clinician should plan to routinely administer fluids and measure electrolyte levels. A basic plan and knowledge of the methods and agents used to treat hypovolemia, severe cardiopulmonary collapse, and life-threatening arrhythmias can result in survival of many critically ill foals.

Clinical use of positive-pressure ventilation in the horse

Positive-pressure ventilation is used to provide improved ventilatory support during anesthesia in the horse. Because of the horse's size and the physiologic changes it undergoes during anesthesia, however, the use of positive-pressure ventilation does not always provide the improvement seen in smaller species. Careful attention to respiratory rate, inspiratory pressure, and I:E ratio minimizes the negative aspect of IPPV on the cardiovascular system. The goal of future ventilatory techniques will be to improve oxygenation without cardiovascular compromise and to do so at a reasonable cost to the client.

Cardiopulmonary effects of xylazine sedation in the foal

Six healthy foals underwent instrumentation for measurement of the cardiopulmonary effects of sedation with 1.1 mg/kg bodyweight xylazine hydrochloride given intravenously. Responses to xylazine in foals at 10 and 28 days of age were not significantly different. Foals became sedate and markedly ataxic, and four of the six foals became recumbent. Heart rate decreased significantly but no arrhythmias were detected. Arterial blood pressure increased initially and then fell significantly below pre-injection values. Changes in respiratory airflow, upper airway obstruction and respiratory noise were noted in the initial 20 mins of sedation, after which respiratory rate fell, tidal volume increased, and minute volume decreased gradually. Arterial blood gas tensions and pH did not change significantly during the 120 mins following xylazine administration. Control studies showed no significant changes. All foals recovered uneventfully.