RETROSPECTIVE ANALYSES OF THE NEUTROPHIL TO LYMPHOCYTE RATIO IN PRIMATES HOUSED AT A SINGLE ZOO

Area of Science:

• Veterinary Medicine
• Primate Research
• Biomarker Discovery

Background:

• The neutrophil-to-lymphocyte ratio (NLR) is a recognized biomarker for inflammation and stress in humans.
• Limited research exists on NLR in nonhuman primates, with prior studies focusing on age, sex, rearing, and acute stressors.

Purpose of the Study:

• To investigate the influence of demographic factors (age, sex, rearing) on NLR in nonhuman primates.
• To assess NLR as a stress marker by comparing routine versus clinical event samples.
• To determine if immobilization methods affect NLR.
• To evaluate the association between routine NLR and mortality risk.

Main Methods:

• Analysis of blood samples from 377 nonhuman primates across 23 species at the Saint Louis Zoo.
• Generalized linear mixed-effect models for demographic and stressor effects.
• Cox proportional hazards models for mortality risk analysis by taxonomic groups.

Main Results:

• Demographic effects on NLR varied significantly by species, with sex impacting NLR in only four species.
• NLRs were significantly higher during clinical events compared to routine events in lemurs and African/Eurasian monkeys, but not in Central/South American monkeys or great apes.
• Inhalation and hand injection immobilization methods were associated with lower NLRs.
• Routine NLR did not predict mortality risk across any taxonomic group.

Conclusions:

• NLR is a variable biomarker in nonhuman primates, influenced by species-specific demographics and physiological states.
• NLR can serve as a stress indicator in certain primate groups, particularly during clinical events.
• Immobilization methods can influence NLR, necessitating careful consideration in research and clinical practice.
• Routine NLR is not a reliable predictor of mortality risk in nonhuman primates.