General approach to surgery and anesthesia in large animals
In large animal species, surgery may be performed in the standing sedated animal, in the recumbent sedated animal or with the animal under general anesthesia and either in lateral recumbency (most common) or in dorsal recumbency. The preferred approach to surgery depends on the species, facilities, procedure and veterinary comfort.
Many procedures are performed in horses using standing sedation and local blocks. This avoids the risk of general anesthesia and can make surgery easier due to the position, height and decreased blood loss.[ Standing patients bleed less due to lower blood flow to the head and back.] However, standing procedures can be more dangerous for the veterinarian and any assistants; patient selection is important.
Horse surgery is rarely done with the animal just sedated and in lateral recumbency. They don’t just lie down and are dangerous if they get too light (too awake under anesthesia). Instead, horses are typically fully anesthetized. However, horses are rarely intubated for field procedures as there is no oxygen source or ventilator available in those situations.
While it is sometimes necessary (ex: castration), general anesthesia in horses can be challenging due to horse’s fight or flight response. Horses tend to react rather than think; this can lead to dangerous situations particularly when they are waking up from anesthesia in a foreign environment. Large horses can also develop myopathies and neuropathies due to the pressure of the large body weight on bony prominences. Finally horses tend to not ventilate well and hence have poor oxygenation under anesthesia. This means most field anesthesia is restricted to short procedures (under 60 minutes). Field recoveries are typically smooth and uneventful as the horse is waking up in its usual environment.
Cattle surgery is typically performed standing.
Bloat occurs rapidly in the recumbent animal (whether sedated or under general anesthesia) and can lead to respiratory difficulty and poor venous return to the heart. Cattle may not even require sedation but will stand quite well for surgery using only local anesthesia (local block or epidural).
Recumbent surgery is more common in calves and is required for hernia repair, some abdominal procedures and for many teat surgeries. Depending on the health of the animal, the patient may be heavily sedated with a local block used for analgesia or the animal may be fully under general anesthesia. Unless performed in a hospital with oxygen and anesthesia machines, patients are not intubated. Intubation requires a much deeper plane of anesthesia than is required for most procedures and increases the risk involved in field anesthesia (since the benefits are limited).
Small ruminants, camelids and pigs
Most small ruminant procedures are performed with the patient recumbent. While you could do surgery in a standing goat, you would need facilities that allowed the animal to be lifted to a better working height and to be restrained with a head gate or chute. This is most likely on a working dairy goat farm. The rest of your small ruminant patients will usually be sedated in lateral recumbency. Camelids will tend to kush (lie down) regardless of what you do but some will stay standing. Pigs do the opposite of whatever you want and noisily. Rarely are these animals intubated in the field; however, small animal machines can be used on many of these animals in the clinic. If the animal can be brought into the facility, intubation and inhalant anesthesia are very useful for more involved or longer procedures.