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Class of Horse

Foals

Foals commonly undergo general anaesthesia and surgery to treat angular or flexural limb deformities ("bent legs").

Foals may also undergo general anaesthesia and surgery to treat injuries, infections, colic or ruptured bladder.

In general, the specific risks associated with anaesthesia and surgeries of newborn foals are related to the immaturity of their physiological systems.

Any condition which causes stress to a foal may predispose the foal to gastric ulceration. This may lead to perforation of the stomach or intestine and subsequent death. To minimise stress, foals are kept with the mare as much as possible in the induction of and recovery from anaesthesia.

Colic surgery in foals is a high risk procedure and foals are susceptible to all of the complications of colic.

In particular, colic surgery in foals is associated with an increased risk of "adhesion formation" (internal scarring within the abdomen), which can lead to subsequent episodes of colic and possibly death.

Foals with ruptured bladders are high risk patients. They are unable to excrete potassium from the body. High blood potassium can cause serious heart problems and death if not corrected. These cases are treated medically before surgical repair is performed under general anaesthesia however the effects of electrolyte imbalances make the foal more susceptible to the adverse effects of anaesthetic drugs.

Pregnant mares

Pregnant mares may undergo general anaesthesia and surgery for treatment of a variety of conditions including injury, infection, colic and foaling difficulties.

General anaesthesia during pregnancy carries a risk of abortion. This risk is extremely low, especially in the first two thirds of pregnancy. When possible, elective surgery under general anaesthesia in heavily pregnant mares is avoided. There is no evidence that any of the anaesthetic drugs commonly used in horses cause foetal damage or loss.

Anaesthesia in pregnant mares also carries increased risks associated with reduced heart function, blood flow and respiration. Pregnant mares have an increased risk of catastrophic limb fracture during recovery from anaesthesia. Limb fracture usually results in death of the mare.

Stallions

Stallions may undergo general anaesthesia and surgery for treatment of a variety of conditions including injury, infection and colic.

Specific risks associated with surgery on stallions are related to temperament and size. Stallions may be at increased risk of myositis (muscle injury) or neuropathy (nerve injury) because of their increased muscle mass and weight. Temperament may lead to poor anaesthetic induction or recovery which can lead to injury.

Sperm production and fertility can be affected by any condition which causes a stress reaction in a stallion; these conditions can include pain, infection, high temperature, general anaesthesia and surgery

Older Horses

Older horses may undergo general anaesthesia and surgery for treatment of a variety of conditions including injury, infection and colic.

Ageing is associated with less effective organ function, diseases affecting metabolism, lameness, reduced joint flexion, osteoporosis ("weak bones") and muscle weakness. All of these factors are associated with increased risks for general anaesthesia and surgery.

Sick Horses

Horses which are suffering from underlying illness may need to undergo general anaesthesia and surgery for treatment of a variety of conditions including injury, infection and colic.

There is an increased risk associated with anaesthesia and surgery of sick horses.

The underlying illness may be associated with less effective organ function, including a lower ability to cope with the adverse effects of anaesthetic drugs and an increased susceptibility to infection.

The underlying illness can result in severe and potentially life threatening consequences.

Medical treatment including fluid therapy may be recommended prior to performing surgery in some cases.

The advantages and disadvantages of performing surgery on any sick horse are considered and discussed prior to a decision being made.

Fit Athletic Horses

Fit athletic horses may undergo general anaesthesia and surgery for treatment of a variety of conditions including injury, infection and colic.

There is an increased risk associated with anaesthesia of fit horses. Fit horses often have significantly lowered respiratory and heart rates during anaesthesia. Fitness, coupled with the effects of the anaesthetic drugs can lead to decreased heart and lung function and to low blood pressure which can result in severe and potentially life threatening consequences.

It is common practice for fit horses to be rested or "let down" for a period of time before elective surgery.