Sedation, anaesthesia and analgesia for farm animals in the field – why is it important?

Analgesia Seda

Pain in farm animals either following surgery or secondary to disease is not only a welfare issue, but evidence suggests that it results in increased morbidity and poor weight gain, thus directly impacting on profitability.

There can be perceived barriers or reasons for substandard provision of analgesia including time of administration, cost, licensing, meat and milk withdrawal periods, poor recognition of pain and perceived benefits of pain in that it allows protection of the affected area. Recognition of pain in these prey species can be challenging, but acknowledging the likely degree of pain and duration can allow rational analgesic plans to be generated.

The use of pre-emptive, multimodal analgesia will always provide superior results in our patients as it prevents perception and transmission of pain. Acute pain can often be managed relatively easily once the underlying cause is addressed. However, management of chronic pain, such as chronic lameness, can be extremely challenging as the prolonged stimulation leads to hyper-algesia and wind-up which ultimately becomes a pain cycle that can be challenging to break without long courses.

There are 5 classes of drug that have analgesic properties that we can consider for use in our patients:

• NSAID’s
• local anaesthetics
• alpha-2 agonists
• ketamine
• opioids 

We have no opioids licensed for use in food-producing animals and the use of alpha-2 agonists is often precluded due to the profound sedation and recumbency that is associated with their administration. Data suggests that use of more than one drug that acts upon different parts of the pain pathway provides superior analgesia – so-called multi-modal analgesia. Route of administration of these classes of drug can also dramatically impact on the success of pain management in individual cases. We are obviously familiar with intravenous, intramuscular and subcutaneous administration, but oral, topical, epidural, perineural, periarticular and regional analgesia can be very effective. Nerve blocks could perhaps be better utilised in more cases allowing provision of superior analgesia and thus welfare. Splints and blocks can prove invaluable for management of distal limb pain.

Sedation and anaesthesia

In elective cases, preparation for sedation and anaesthesia can help to reduce morbidity and mortality, particularly regarding with-holding food prior to recumbency. Sedation is primarily provided by administration of alpha-2 agonists. However, administration of these drugs in small ruminants should be used with caution and other options are limited but available. Anaesthesia is not undertaken as frequently in ruminants as in other species, but for certain procedures can be extremely useful and may be more appropriate than heavy sedation. Ketamine is the most commonly used induction agent. It has many advantages, but its use can be challenging due to its short half-life when used in the field.

In summary, appropriate use of sedative, anaesthetic and analgesic drugs can not only make it easier to more effectively undertake procedures but provide superior care and improve welfare in our patients.