xylazine (0.2 mg/kg IV) to a bull to produce immobilization for wire placement during mandibular fracture repair. No additional local anesthetic was needed during the wiring process. The duration of deep sedation was 30 minutes and the bull stood within an hour after administration of the drugs [138]. Diazepam (0.1 mg/kg IV) and butorphanol (0.1 mg/kg IV) induce recumbency for a short period of time in camelids [139].
Midazolam (0.2 mg/kg IV) was able to reduce the response of sheep to painful mechanical stimulation [130]. In goats, IM midazolam (0.6 mg/kg) induced 20 minutes of sedation. Hypnosis with recumbency occurred and lasted for 10–20 minutes when midazolam was administered intravenously at 0.6 and 1.2 mg/kg. Increasing the dose to 1.2 mg/kg enhanced the degree of reflex suppression, and the animals appeared to be in a light plane of anesthesia as indicated by the lack of response to mechanical stimulation applied using the tail base clamp [140]. In goats with urethral obstruction, when the effect of increasing the urine output of xylazine is contraindicated, diazepam or midazolam can be given alone or with other anesthetics to induce anesthesia. Flumazenil, a benzodiazepine antagonist, can be administered at 0.02 mg/kg IV or a 1 : 13 ratio (1 part of flumazenil to 13 parts of diazepam) to antagonize the CNS effects of diazepam and midazolam [10].
2.5.2 Swine
Diazepam has been given to miniature pigs at doses from 5.5 to 8.5 mg/kg IM with maximal sedation occurring within 30 minutes following administration [22]. Prolonged recovery has occurred when large doses of diazepam are given intramuscularly to older sows and boars. A continuous rate infusion (CRI) of diazepam (CRI: 1 mg/kg/hour IV, following 0.5–10 mg/kg IM and 0.44–2 mg/kg IV) has been used in pigs to maintain long‐term hypnosis and sedation for up to 6 hours in a research setting [141, 142]. Satisfactory sedation with 0.1–0.5 mg/kg of midazolam IM has been reported [18], whereas a calming effect and sedation occur within 3–4 minutes following intranasal administration of 0.2–0.4 mg/kg of the drug [143]. In piglets and adult swine, midazolam administered either intramuscularly or intranasally at 0.1–0.2 mg/kg produced effective tranquilization [143, 144]. Midazolam (1 mg/kg IM) has been combined with azaperone (4 mg/kg IM) to produce preanesthetic tranquilization prior to induction with propofol [145]. Midazolam in general has minimal cardiopulmonary effects. However, it has been shown to cause a 20% decrease in heart rate and 50% decrease in respiratory rate in pigs receiving 0.1 mg/kg IM of midazolam [144].
2.6 Chloral Hydrate
Chloral hydrate was one of the first general anesthetics used in large animal practice. Chloral hydrate itself does not have a CNS‐depressing effect; it depends on its metabolite, trichloroethanol, to produce sedative and anesthetic effects. This latency of action as well as the narrow margin of safety of the drug makes it an undesirable anesthetic for use in clinical practice. Nonetheless, chloral hydrate is a very reliable sedative. In horses, chloral hydrate is often administered as an alternative when other tranquilizers or sedatives fail to produce the desired calming effect. Chloral hydrate does not have an analgesic effect, thus an additional analgesic is required if the animal is in pain or the procedure being performed is painful. Chloral hydrate is very irritating to the tissue. Therefore, IV injection of the drug is better via an IV catheter to prevent accidental perivascular injection and the consequential severe tissue damage. Chloral hydrate has been used to sedate unapproachable but confined cattle via oral administration. Water should be withheld for 24–36 hours prior to offering the animal diluted chloral hydrate drinking solution to ensure complete consumption of the drug. The dose recommended for oral administration is 100–150 g in 8–12 l of water per animal for sedation and 5–7 g per 100 kg (220 lb) for light to moderate narcosis [146].
In pigs, oral chloral hydrate (13 g/50 kg [110 lb]) produced sedation within 20–30 minutes following administration via a stomach tube [147]. Though intraperitoneal administration (4–6 ml of 5% solution/kg) has been reported in the pig, the technique is not recommended as peritonitis is a common complication [148]. However, Jennings reported intraperitoneal chloral hydrate administration (0.3 mg/kg in 5% solution) produced sedation within 30 minutes with a duration of 60 minutes. No tissue irritation or signs of peritonitis were observed [146]. Chloral hydrate (1–4 ml of 5% solution) has been used in combination with azaperone (4 mg/kg IM) in 500 pigs to produce general anesthesia for 2 hours with complete recovery to standing within 4–5 hours [149].
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