Reference intervals and physiologic alterations in hematologic and biochemical values of free-ranging desert tortoises in the Mojave Desert

Desert tortoise (Gopherus agassizii) populations have experienced precipito us declines resulting from the cumulative impact of habitat loss, and human and disease-related mortality. Evaluation of hematologic and biochemical r esponses of desert tortoises to physiologic and environmental factors can f acilitate the assessment of stress and disease in tortoises and contribute to management decisions and population recovery. The goal of this study was to obtain and analyze clinical laboratory data from free-ranging desert to rtoises at three sites in the Mojave Desert (California, USA) between Octob er 1990 and October 1995, to establish reference intervals, and to develop guidelines for the interpretation of laboratory data under a variety of env ironmental and physiologic conditions. Body weight, carapace length, and ve nous blood samples for a complete blood count and clinical chemistry profil e were obtained from 98 clinically healthy adult desert tortoises of both s exes at the Desert Tortoise Research Natural area (western Mojave), Goffs ( eastern Mojave) and Ivanpah Valley (northeastern Mojave). Samples were obta ined four times per year, in winter (February/March), spring (May/June), su mmer (July/August), and fall (October). Years of near-, above- and below-av erage rainfall were represented in the 5 yr period. Minimum, maximum and me dian values, and central 95 percentiles were used as reference intervals an d measures of central tendency for tortoises at each site and/or season. Da ta were analyzed using repeated measures analysis of variance for significa nt (P < 0.01) variation on the basis of sex, site, season, and interactions between these variables. Significant sex differences were observed for pac ked cell volume, hemoglobin concentration, aspartate transaminase activity, and cholesterol, triglyceride, calcium, and phosphorus concentrations. Mar ked seasonal variation was observed in most parameters in conjunction with reproductive cycle, hibernation, or seasonal rainfall. Year-to-year differe nces and long-term alterations primarily reflected winter rainfall amounts. Site differences were minimal, and largely reflected geographic difference s in precipitation patterns, such that results from these studies can be ap plied to other tortoise populations in environments with known rainfall and forage availability patterns.