Effect of estrous cycle phase on clinical pathology values in beagle dogs

In dogs, the diestrus phase is considerably longer than in most domestic animals, and is characterized by high circulating progesterone concentrations that may influence clinical pathology values.

The objective of this retrospective study was to investigate differences in clinical pathology data in dogs in diestrus compared with data from dogs in all other phases of the estrous cycle.

Phase of the estrous cycle was determined by histologic evaluation of reproductive tissues from 86 control female Beagles that had participated in 23 toxicity studies. Serum biochemical, hematologic, and urinalysis values from dogs in diestrus were compared with data from dogs in all other estrous cycle phases using a 2-tailed t-test.

In Beagles in diestrus (n = 38), serum cholesterol concentrations and eosinophil counts were 35% (P < .0001) and 45.8% (P = .0035) higher, respectively, than for Beagles in all other phases of the estrous cycle (n = 48). Furthermore, Beagles in diestrus had 14% lower AST activity (P = .0011), 1% lower chloride concentration (P = .0224), 7.8% lower hemoglobin concentration (P < .0001), 7.8% lower RBC count (P < .0001), and 7.6% lower hematocrit (P < .0001) compared with female dogs in all other phases of the estrous cycle. Urine values did not differ significantly between groups.

Differences in clinical pathology values between dogs in different phases of the estrous cycle could potentially confound interpretation of data in toxicity studies, which often have small group sizes. Interpretation of clinical pathology data in female dogs should be performed with due consideration given to the phase of the estrous cycle.