In large animal species, surgery may be performed in the standing sedated animal, in the recumbent sedated animal (dangerous) 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. Veterinarians can be injured even with horses restrained in stocks.
Recumbent horse surgery usually requires general anesthesia rather than just sedation. However, horses are rarely intubated for field procedures as there is no oxygen source or ventilator available in those situations. Anesthesia is maintained through repeated injections or iv infusion protocols.
Horses are not the best anesthesia candidates. They tend to ventilate poorly and often have poor oxygenation when under general anesthesia. Horses also have strong flight or fight responses and tend to react rather than think, particularly in foreign environments. Field anesthesia is usually safe and effective if it is 1) kept to less than 60 minutes and 2) done in a safe outdoor space.
If injectable anesthesia is required for more than 60 minutes, the risk of complications and rough recovery increases. Large horses can also develop myopathies and neuropathies due to the pressure of the large body weight on bony prominences.
Hills, traffic and physical obstacles can be issues during recovery. Open grassy fields away from roads are ideal. Stall recoveries are dangerous places for both the waking horse and surgeon. Recovery stalls are necessary in hospital environments but typically are padded and have safe observation decks and exit plans.
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.