The Influence of Body Size, Season, Sex, Age and Other Factors upon Some Blood Parameters in Small Mammals

Abstract

Measurements were made of hemoglobin concentration, hematocrit ratio, mean corpuscular hemoglobin concentration (MCHC) and erythrocyte diameter in 34 species of wild mammals from widely separated areas in the United States and Canada representing 5 orders, 10 families and 25 genera. Included in these determinations were measurements on two races of Tamias striatus , two races of Oryzomys palustris , two races of Peromyscus leucopus and three races of Peromyscus maniculatus . Differences in blood values related to species, age, body size and other factors were evident. Hemoglobin concentrations, hematocrit ratios and MCHC's showed a correlation with body size, smaller species generally having higher blood values. A number of exceptions were noted which were probably related to season, altitude, behavior or special physiological adaptations. Members of the families Soricidae and Vespertilionidae which include many small-bodied forms with high rates of metabolism generally had the highest blood values. Pregnant and lactating females usually had lower mean blood values than non-gravid females and males, but no significant differences were found between adult non-gravid females and males. Hemoglobin and hematocrit values in juveniles were often significantly lower than in adults. There was some indication that erythrocyte size was larger in juveniles than in adults, and this may have compensated in some unexplained way for the lower hemoglobin and hematocrit values. No significant differences were noted between the blood values of immatures (subadults) and adults. Seasonal differences in mean blood values were observed in cotton rats ( Sigmodon hispidus ), harvest mice ( Reithrodontomys fulvescens ) and deer mice ( Peromyscus leucopus , P. maniculatus and P. boylii ). Lower blood values in summer in cotton rats could possibly be correlated with either increase in weight or increase in the ambient temperature of the environment during this season. A tendency for high-altitude forms to have higher mean blood values than forms living at low altitudes was noted, but it was inferred from the data that the differences were probably mainly due to differences in ambient temperature. High blood oxygen capacities associated with high hemoglobin and hematocrit values in species of small body size with high metabolic rates would be a distinct advantage in increasing the delivery of oxygen to the tissues. The advantage of increased blood oxygen capacity of the smaller species coupled with a higher carbonic anhydrase activity in their red cells is discussed.