Anesthesia Guidelines: Ruminants

Find guidelines for ruminant anesthesia, including recommended anesthetic drugs and procedures.

Research Animal Resources (RAR) veterinary staff designed these guidelines to be general recommendations, not an inclusive list of all possible drug combinations that can be used in ruminants.

Consequently, guidelines do not reference to specific research-associated concerns. If you have questions about using anesthetics for your particular situation, please work with your area veterinarian to develop the most effective anesthetic plan.


Species-specific considerations

Bloat

Gross distention of the rumen is a problem with prolonged anesthesia. Rumen distention can impede diaphragm function, leading to abnormalities in breathing and oxygenation.  

Bloat or rumen distension can be minimized by fasting ruminants for a minimum of 24 hours. Bloat can be also minimized by passing a rumen tube, and administering Magnalax through the rumen tube (~480 mls). 

Regurgitation  

Regurgitation during anesthesia can be a problem in ruminants due to large volumes of food in the forestomach.

Anesthesia depresses the swallowing reflex, which increases the risk of aspirating stomach contents into the lungs. Active regurgitation can occur at light levels of anesthesia, especially when the larynx is stimulated by intubation.

Regurgitation can be avoided by:

  • Administering additional anesthetic if swallowing, coughing, or chewing are noted while preparing to intubate. 
  • Lowering the head of the animal and suctioning of the mouth, to facilitate fluid drainage. 
  • Decreasing the depth of anesthesia (if using an inhalation agent). Passive regurgitation occurs with deeper levels of anesthesia and is characterized by a stream of stomach fluid draining from the mouth. Decreasing the depth of anesthesia (if using an inhalation agent) may cause this response to cease.
  • Intubating with a cuffed endotracheal tube if ruminants are to be anesthetized for longer than 20 minutes. This helps decrease the risk of aspirating regurgitated rumen contents.
  • Placing a rumen tube to decrease the risk of aspiration.

General considerations

Acclimation

Do not use newly arrived animals for experimental procedures until 72 hours after entry into the facility. A one-week acclimation period is recommended. This stabilization period is not required for animals used acutely (anesthetized and euthanized at the end of the procedure), although it is recommended. This provision allows animals to acclimate to the facility and reduces the chance of stress-induced disease, including anesthetic death.

Padding and positioning

Proper padding and optimal positioning of ruminants during surgery is important. Whenever possible, standing surgeries with local anesthetic blocks are preferred. However, if recumbency is required, place ruminants on a flat surface with sufficient padding. A minimum of one- to two-inch thickness is recommended for calves, sheep, and goats. Because of their size, ruminants often require mechanical ventilation during anesthetic procedures.

Fasting

Fast animals for 24 hours prior to an anesthetic event.   

Heat

Because most anesthetic drugs cause hypotension and hyperthermia, provide supplemental heat under anesthesia. Despite having wool, sheep become hypothermic during anaesthesia and standard methods should be used to maintain body temperature (insulating blankets, heating pads, etc.). Regardless of heat source, never place animals directly on the heat.

Catheterization

Following sedation, place an indwelling catheter to administer anesthetic drugs, emergency drugs, and intravenous fluid support. The most common site for catheter placement is the jugular vein. Appropriate sizes for jugular catheterization: 16G or 18G in sheep, goats, or calves, and 12G or 14G in adult cattle.  

Fluid support

It is important to provide supplemental fluid support. Appropriate fluid rates range from 5-10 mls/kg/hour, and may vary based on the anesthetic combination used.  

Rumen tubes

Due to the propensity for ruminants to regurgitate and/or develop bloat, place a rumen tube in anesthetized ruminants. 

Monitoring

Standard mammalian monitoring techniques apply to ruminants. The goal of monitoring should be to maintain cardiovascular homeostasis and core body temperature.

Understanding the basic physiologic effects of the anesthetics used is paramount to correctly interpreting monitoring parameters. View description of anesthetic agents.

Parameters to be monitored in anesthetized ruminants include anesthetic depth, heart rate, respiratory rate, oxygen saturation, expired CO2 (EtCO2), temperature, blood pressure, and mucous membrane color.

Normal ranges (without anesthesia)

  • Temperature = 101-104°F (sheep, goats); 100-102.5°F (calves); 101.5-103.5°F (adult cattle)
  • Heart rate (beats/minute) = 60-120 (sheep, goats); 100-120 (calves); 55-80 (adult cattle)
  • Respiratory rate (breaths/minute) = 10-30 (sheep, goats, adult cattle); 15-40 (calves)
  • Blood pressure: >60 mm Hg (mean) and >90 mm Hg (systolic)
  • Oxygen saturation = >95%
  • EtCO2: 35-45
  • Mucous membranes = pink, not pale, white, gray, or blue

Normal ranges (with anesthesia)

  • Temperature = >98°F
  • Heart rate (beats/minute) = 80-120 (sheep, goats, calves); 70-100 (adult cattle)
  • Respiratory rate (breaths/minute) = 30-40 (sheep, goats, calves); 20-40 (adult cattle)
  • Blood pressure: >70 mm Hg (mean) and >100 mm Hg (systolic)
  • Oxygen saturation = >95%
  • EtCO2: 35-45 
  • Mucous membranes = pink, not pale, white, gray, or blue

For more involved procedures, EKG, invasive pressure monitoring, and blood gas analysis may be indicated.  


Anesthetic drugs and procedures

Ruminant anesthesia is generally broken up into premedication (sedation), anesthetic induction, and anesthetic maintenance.  

As with other species, anesthesia (maintenance) can be accomplished via inhalation or parenteral methods.  

Sedation

Sedation

Administering sedative drugs decreases excitement and causes relaxation to allow for the placement of indwelling catheters (for IV drug and fluid administration) or allow for intubation (for inhalation anesthesia).

Induction is often required in addition to sedation to provide a sufficient level of sedation/anesthesia for intubation.

The anticholinergic glycopyrrolate (0.004-0.01 mg/kg IM) may be used as a premedication to dry oral and respiratory secretions and for its vagolytic (ability to block vagal nerve stimulation and consequent bradycardia) effects during endotracheal intubation.

In ruminants, anticholinergics may make secretions more viscous. These agents can also reduce normal stomach contractions. For these reasons, anticholinergics are not routinely used in ruminants.

For sedation, the intramuscular (IM) route is most common.


Acepromazine

Dose: 0.05-0.2
Route: IM
Comments: Slow onset of mild sedation, usually without recumbency.


α-2 Agonists 

Rapid onset of profound sedation, often with recumbency.

Xylazine

Dose: 0.05-0.2
Route: IM
Comments: Recumbency for ~60 minutes. Alpha 2 agonists such as xylazine may cause adverse pulmonary changes and hypoxemia in sheep, especially when given at high dose or IV. For xylazine reversal, use yohimbine (0.1- 1.0 mg/kg IV) or atipamezole (0.1-0.2 mg/kg IV or IM).

Dexmedetomidine

Dose: 0.015 mg/kg 
Route: IM
Comments: Alpha 2 agonists such as dexmedetomidine may cause adverse pulmonary changes and hypoxemia in sheep, especially when given at high dose or IV. Use atipamezole for dexmedetomidine reversal: 0.1-0.2 mg/kg IV or IM.


Benzodiazepines

Provide muscle relaxation, hypnosis, decreased anxiety, and mild sedation.

Diazepam

Dose: 1.0-1.5
Route: IM
Comments: Reversal for diazepam or midazolam can be accomplished with flumazenil (0.02 mg/kg IV or IM).

Midazolam

Dose: IM
Route: 0.5-1.0
Comments: Reversal for diazepam or midazolam can be accomplished with flumazenil (0.02 mg/kg IV or IM).


Dissociatives

Ketamine

Dose: 10-15 
Route: IM

Telazol 

Dose: 4-6
Route: IM


Combinations

Ketamine + Xylazine 

Dose: Ketamine: 11 mg/kg + Xylazine: 0.20 mg/kg
Route: IM
Comments: Xylazine must be given first. 

Ketamine + Dexmedetomidine

Dose: Ketamine: 0.015 mg/kg + Dexmedetomidine: 1 mg/kg 
Route: IM
Comments: Alpha-2 agonists such as dexmedetomidine may cause adverse pulmonary changes and hypoxemia in sheep, especially when given at high dose or IV. Use atipamezole for dexmedetomidine reversal: 0.1-0.2 mg/kg IV or IM. 

Induction

Induction

Induction refers to an anesthetic administered to place an animal in an unconscious state and allow for tracheal intubation.


Isoflurane

Dose: 3-5%
Route: Inhalation/facemask


Propofol 

Dose: 2-6 mg/kg 
Route: IV
Comments: Should be given to effect. Propofol causes respiratory depression. Any animal receiving propofol should be intubated following administration.


Pentobarbital

Dose: 10-12 mg/kg
Route: IV
Comments: Should be given to effect. Causes profound respiratory depression. Any animal receiving pentobarbital should be intubated following administration.

Maintenance

Maintenance

Maintenance refers to drugs administered to keep animals unconscious and allow for surgical (or other) procedures to be performed.

Parenteral administration: For parenteral administration of maintenance anesthesia, the intravenous (IV) route used.

Endotracheal intubation: Inhalation anesthesia may be delivered by a facemask, but is generally delivered via endotracheal intubation. If ruminants are to be anesthetized for longer than 20 minutes, intubate with a cuffed endotracheal tube to decrease the risk of aspirating regurgitated rumen contents.

  • Ruminants can be intubated with the use of a laryngoscope.
  • Endotracheal tube sizes vary. A good starting point for small ruminants is a 7.5-9.0 mm internal diameter. Larger ruminants will require larger tubes, depending on their size. It is important to have several sizes available and ready with appropriate ties when attempting intubation.
  • Applying sterile surgical lubricant to the tip of the endotracheal tube will help facilitate intubation.
  • The endotracheal tube should extend approximately from outside of the mouth to the thoracic inlet. This can be used as a guide for how far the tube should be inserted upon intubation. 
  • Verify proper placement of the endotracheal tube by ausculting all lung fields for strong breath sounds. If no breath sounds are heard, back the tube out until sounds are heard in all lung fields. 
  • Endotracheal tubes need to have a cuff and cuffs need to be inflated during anesthesia. Inflate the cuff just enough to stop gas leakage. Over-inflation of the endotracheal tube cuff can damage the trachea.

Gas anesthesia machines: Facemasks and intubation require gas anesthesia machines with an oxygen source and a precision vaporizer. For ruminants, use a rebreathing system.

Gas scavenging systems: When using inhalant anesthesia, use an anesthetic system equipped with a gas scavenging system to minimize occupational exposure to exiting gases.

Ophthalmic ointments: For anesthetic events lasting more than five minutes and whenever facemasks are used, apply an ophthalmic ointment (e.g., Paralube® or Lacrilube®) to eyes to prevent corneal drying and trauma.


Isoflurane

Dose: 1-3% 
Route: Inhalation/facemask
Comments: Given to effect.


Propofol 

Dose: 5-7 mg/kg/hour constant rate infusions (CRI) after bolus induction
Route: IV

References for these guidelines are available by request.