Category of Invasiveness

Canadian Council on Animal Care:

  • Established in 1968, the CCAC has established enhanced animal care and use programs within the scientific community through its voluntary compliance, education and code of ethics
  • The CCAC is a national peer review organization with a mandate to work for the improvement of animal care and use on a Canada wide basis 
  • Its Assessment Program focuses on institutional animal care and use programs, and the functioning of the local Animal Care Committee


All animal protocols using vertebrates or invertebrates must be assigned a CCAC category of invasiveness in animal experimentation

CCAC categories of Invasiveness:

Category A

Experiments on most invertebrates or on live isolates. 

  • Tissue culture
  • Tissues obtained at necropsy or from the slaughterhouse
  • Use of eggs, single celled organisms, protozoa and metazoa

Category B

Experiments that cause little or no stress or discomfort. 

  • Maintenance of domestic herds/flocks
  • Commercial herd/flock production
  • Short term and skillful restraint of animals for observation or physical examination
  • Blood sampling
  • Injection of material via intravenous, intramuscular, subcutaneous, intraperitoneal and oral routes with no known adverse reaction
  • Short periods of water and/or food deprivation equivalent to periods of abstinence in nature
  • Acute non survival studies

Category C

Experiments which cause minor stress or pain of short duration.

There should be no significant alterations to the animal’s appearance, or physiological parameters such as respiratory and heart rates, food and water intake and urine and fecal output.

In addition, category “C” animals must not demonstrate any self mutilation, dehydration, anorexia or alterations in behaviour (aggression, withdrawal, increased or decreased recumbency or dormancy, social interactions)


  • Cannulation or catheterization of blood vessels or body cavities under anesthesia
  • Minor surgical procedures under anesthesia (biopsies, laparoscopy)
  • Short periods of restraint beyond that for simple observation with minimal distress
  • Short periods of water and/or food deprivation exceeding periods of abstinence in nature
  • Exposure to non lethal doses of drugs or chemicals

Category D

Experiments which cause moderate to severe distress and discomfort.

Procedures in Category D should not cause prolonged or severe distress evident by the following clinical signs: abnormalities in behaviour, absence of grooming, dehydration, abnormal vocalization, immobility, prolonged anorexia, indications of severe local or systemic infection or extreme lethargy.


  • Major survival surgical procedures under general anesthesia
  • Behavioural stresses (maternal deprivation, aggression, predator-prey interactions)
  • Physical restraint for prolonged periods (several hours or more)
  • Exposure to chemical/drugs that impair physiological systems
  • Production of radiation sickness
  • Use of Freund’s Complete Adjuvant
  • Induction of anatomical or physiological abnormalities that cause pain and distress
  • Exposure to noxious, inescapable stimuli
  • Procedures causing severe, persistent or irreversible disruption/malfunction of the sensorimotor centres

Category E

Experiments that cause severe pain near, at or above the pain tolerance threshold of conscious, unanesthetized animals.

This category is not restricted to surgical procedures, and includes exposure to noxious chemicals or agents with unknown or ill-defined effects, or that markedly impair physiological systems causing extreme distress, pain and death. Death is often the endpoint.


  • Use of muscle relaxants or paralytic agents without anesthesia
  • Injection of noxious substances
  • Induction of severe stress or shock
  • Extremely invasive surgical procedures
  • New biomedical experiments with a high degree of invasiveness
  • Burn or trauma infliction on unanesthetized animals
  • Any experiment where the pain cannot be relieved by analgesia


Major Surgery

  • A survival procedure with direct visual access to a major body cavity (cranium, thorax, spinal canal, abdomen, pelvis)
  • Exposure of major vascular, lymphatic, muscular, skeletal, or glandular structures
  • Removal and /or alteration to a functionally significant amount of viable tissue

Minor Surgery

  • A surgical procedure that does not result in removal or alteration to a functionally significant amount of viable tissue
  • Often no clear delineation between “major” and “minor” surgery
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