Hematology and Clinical Chemistry Reference Intervals for Inbred Strain 13/n Guinea Pigs (Cavia Porcellus )

Abstract

Inbred Strain 13/N Guinea Pigs are Frequently Used As Animal Models in Studies of Emerging and High-pathogenicity Viruses. To Date, Clinical Reference Intervals Have Not Been Established for Hematology and Clinical Chemistry Parameters in This Strain. We Obtained Whole-blood Samples from the Cranial Vena Cava of Healthy Strain 13/N Colony Animals for Inhouse Cbc and Clinical Chemistry Analyses. Analyte Values Were Investigated to Determine Subpopulation Differences According to Age and Sex. Glucose, Albumin, Alp, Lymphocyte Percentage, Hgb, and Mchc Decreased with Age, Whereas Neutrophil and Monocyte Percentages, Bun, Creatinine, Calcium, and Amylase Increased with Age. Total Protein and Wbc Counts Increased Over the First 300 D of Life Before Stabilizing. Across All Age Categories, Female Guinea Pigs Consistently Had Lower Rbc, Hct, Hgb, Alt, Alp, and Amylase Levels and Higher Mcv Values Than Males. These Trends Were Strongest in Adults (age, 151 Through 900 D). Most Parameters Stabilized by 300 D; Previous Studies Used 60 D or 120 D As Adult Age and 90 to 120 D As Sexual Maturity. We Recommend Age Group Definitions of 0 Through 150 D for Juveniles, 151 Through 900 D for Adults, and Older Than 900 D for Geriatric Adult Strain 13/N Guinea Pigs.

Figure 1.

WBC commonly found in guinea pig blood smears. (A) Lymphocytes have a higher nuclear:cytoplasmic ratio than (D) monocytes. Eosinophils (C) are easily differentiated from (B) neutrophils, which also are known as heterophils in rabbits and guinea pigs, by the larger, more prominent pink granules in eosinophils. (E) Basophils contain large blue-purple granules. (F) Foa-Kurloff cells (F) contain pink intracytoplasmic inclusion bodies of varying size and have shown natural killer activity in vitro. Wright-Giemsa staining; magnification, ×100 (oil immersion).

Figure 2.

Erythrocyte analysis by sex and age in strain 13/N guinea pigs. Erythrocyte number (RBC), Hgb, and Hct are consistently higher in males than females. These parameters peak by 450 d and then decrease over time. Erythrocyte volume (MCV) has a bimodal distribution that is undifferentiated by age or sex. The solid and dashed red lines represent the mean and 95% CI, respectively, of each parameter. The shaded area represents the 95% predictive interval of each parameter.

Figure 3.

Lymphocyte analysis by sex and age in strain 13/N guinea pigs. (A) Changes with age in WBC, neutrophils, lymphocytes, monocytes, eosinophils, and platelets in female and male strain 13/N guinea pigs. (B) Longitudinal sampling of 15 strain 13/N guinea pig pups revealed a steady increase in total WBC and neutrophils and decreasing percentage of lymphocytes over the first 6 mo of life compared with the adult cohort (age, 5–30 mo). The solid and dashed red lines represent the mean and 95% CI, respectively, of each parameter. The shaded area represents the 95% predictive interval of each parameter.

Figure 4.

Effect of age and sex on clinical chemistry in strain 13/N guinea pigs. BUN and creatinine increase with age in strain 13/N guinea pigs. Total protein sharply increases for the first 400 d of life, followed by a steady drop along with albumin concentration, as a secondary sign of protein loss. In addition, calcium and amylase increased with age. The solid and dashed red lines represent the mean and 95% CI, respectively, of each parameter. The shaded area represents the 95% predictive interval of each parameter.

Figure 5.

Effect of age and sex on liver enzymes in strain 13/N guinea pigs. ALP sharply decreases in the first 200 d. Males have a consistently higher ALT than females, but this trend is not seen with AST or GGT. The solid and dashed red lines represent the mean and 95% CI, respectively, of each parameter. The shaded area represents the 95% predictive interval of each parameter.

Figure 6.

Longitudinal sampling of clinical chemistry analytes in 15 strain 13/N guinea pig pups. Total protein (TP) and amylase (AMY) increase with age in strain 13/N guinea pig pups. Albumin (ALB) did not significantly rise in this same period, indicating that most of the protein increase is related to immunoglobulin production in the developing immune system. High ALP levels are often seen at high levels in young, growing animals. Here, ALP appears to reach levels similar to those of adults by 6 mo of age. GGT drops suddenly after 1 mo before steadily increasing within the adult range. Calcium (CA) reaches adult 5-30 mo values by 3 mo and continues to rise through 6 mo.