Pain Management in Food Animals

Pain Management in Food Animals

Overview

  • Presentation by Hilari M French and Eoin Ryan, adapted from A. Jacques Fuselier, DVM, DACT, DABVP.

Types of Analgesics and Anesthetics

  • Injectable Anesthetics:

    • Ketamine: A dissociative anesthetic primarily used for induction of anesthesia and analgesia.

  • Sedatives:

    • Xylazine: Often used for its sedative and analgesic properties.

  • Opioids:

    • Butorphanol: A mixed agonist-antagonist opioid used for pain management in animals.

    • Morphine: A full agonist opioid.

  • NSAIDs (Non-Steroidal Anti-Inflammatory Drugs): Used for managing pain and inflammation.

  • Local Anesthetics:

    • Blocks sodium channels, inhibits conduction and transmission of pain signals.

  • α2-Agonists: Agents such as xylazine that provide sedation and analgesia.

  • Dissociative Anesthetics:

    • Ketamine: Mentioned as a dissociative agent that alters perception of pain.

Pain Processing and Management

  • Perception, Transmission, and Modulation:

    • Pathways involved include the thalamus and spinothalamic tract.

    • Focus on regional anesthesia, epidural, and local anesthetics for pain management.

    • Importance of multimodal analgesia: using different drugs in combination enhances pain relief.

Behavioral Signs of Pain in Food Animals

  • Indicators:

    • Vocalizing or grunting

    • Tail swishing

    • Limping

    • Bruxism (grinding teeth)

    • Laying down

    • Signs of depression

    • Lowering of the head

    • Rigid posture

    • Kicking or stomping

    • Excessive licking of a painful area

    • Reluctance to move

    • Inappetence (loss of appetite)

Physiological Signs of Pain

  • Increased physiological parameters indicating pain include:

    • Respiration rate: Increased during pain

    • Body temperature: Often elevated

    • Heart rate: Increased as well

    • Pupil size: Mydriatic response to pain

  • Caution: These signs can also be a normal stress response.

Assessment of Pain Management Practices

  • Surveys on Pain Management:

    • Canadian veterinary survey on castration revealed low rates of pain management in pigs (0.0015%) and varying rates in calves: 6.9% for beef, 18.7% for dairy.

    • UK survey indicated 57% of adult cattle received epidural anesthesia or post-operative analgesics for laparotomies and C-sections.

    • AABP & AVC survey showed only 20% of respondents provided analgesics or local anesthesia for castration.

    • Brazilian study indicated an 84% consensus amongst large animal veterinarians that their ability to recognize and treat pain was insufficient, with only 58.5% of laparotomies receiving pre-operative analgesics.

Pain Management Strategies

  • Target acute pain efficiently with:

    • Quick-acting analgesics for initial management followed by longer-acting medications:

    • NSAIDs

    • Opioids

    • Local anesthetics

    • NMDA receptor antagonists

    • α2-agonists

  • Emphasizes that a multimodal approach yields the best outcomes.

Local Anesthesia Mechanism

  • Local anesthetics operate by:

    • Blocking sodium channels in nerve cells, reducing the conduction and transmission of pain signals.

    • Effectiveness is reduced in infected tissues due to lower pH levels.

  • Properties of common local anesthetics:

    • Lidocaine:

    • Onset: 2-5 min

    • Duration: 90 minutes (approximately)

    • Increase to 300 min when epinephrine added.

    • Bupivacaine:

    • Onset: 20-30 min

    • Duration: 5-8 hours

  • Methods of administration include intravenous, topical, and local nerve blocks.

Impact of Local Anesthesia at Castration

  • Evidence suggests administration of a local anesthetic during castration can lead to a significant decrease in cortisol levels (by 25%), leading to reduced vocalization and struggling.

  • Considerations regarding efficacy after the anesthetic wears off and suggestions for analgesics like lidocaine and bupivacaine combined with epinephrine (e.g., Tri-Solfen) post-operatively show positive results.

Cortisol Levels and Pain Procedures

  • Data depicted as percentage change in peak plasma cortisol concentration (Cmax) in analgesic-treated calves compared with untreated control calves.

    • Significant insights are garnered from plots visualizing the differences in these treatments.

Surgical Techniques: Castration

  • Described methods involve:

    • OPEN CASTRATION:

    • Perform while the animal is standing in a crush restraint.

    • Clean and dry the scrotal sac followed by local anesthesia (consider xylazine epidural) 15 minutes before incising (about 2-5 inch incision).

    • Utilize emasculator to remove testicular cord, with various surgical challenges to monitor after the procedure such as hemorrhage or infection.

Local Anesthesia in Other Procedures

  • Dehorning/Disbudding:

    • Examining the effectiveness of local anesthesia on cortisol levels indicates stress and pain are reduced, with cornual block providing longer efficacy.

    • Various block techniques have been analyzed, focusing on sensation checks prior to procedures.

Analgesics Available for Food Animals

  • Comprehensive tables provided detail different classes of analgesics, their respective dosages, routes of administration, and indications:

    • Flunixin Meglumine:

    • Approved for use in cattle/swine for fever and inflammation.

    • Route: IV or PO with specific withdrawal times for meat/milk.

    • Ketoprofen:

    • Non-approval for use in cattle in the USA but used in EU and Canada for pain.

    • Requires multiple doses due to short half-life.

    • Meloxicam:

    • Approved in EU & Canada for respiratory diseases, diarrhea, and dehorning pain, with specific comments on availability.

Sedative-Analgesic Combination Therapies

  • The use of opioids, α2-agonists, and NMDA receptor antagonists together synergistically increases analgesic effects, improving animal welfare and reducing risks for operators.

Opioids and Their Mechanism

  • General Function:

    • Bind to specific spinal and supraspinal receptors introducing analgesic effects.

  • Mu Receptor: Causes sedation and may lead to adverse effects like respiratory depression.

  • Butorphanol:

    • Common opioid option providing effective analgesia with fewer adverse effects when used in conjunction with other agents.

Conclusion

  • Importance of continuous research and improvement in pain management practices in food animals for welfare, productivity and to minimize stress during medical procedures.

Questions

  • Open floor for any inquiries regarding pain management in food animals, surgical procedures, and analgesic therapies.