Seasonal Variation in Hematology and Blood Plasma Chemistry Values of the Timber Rattlesnake (Crotalus horridus)

Hematology, biochemical analyses, and body condition indices are useful tools for describing animal health, especially when making management decisions for species of conservation concern. We report hematologic, biochemical, and body condition index data for 13 free-ranging timber rattlesnakes (Crotalus horridus) sampled repeatedly over an active season in Indiana, USA. Hematology, biochemical, and body condition index analyses are useful tools for diagnosing diseases at early stages (Strik et al. 2007) and assessing the relationship between a population's health and the quality of habitat (Allender et al. 2006). Furthermore, changes in environ- mental conditions or disease can cause stress, which can be detected in hemato- logic data (Oppliger et al. 1998), especially if they change over time (Peterson 2002). The monitoring of individuals' data over time is necessary for detecting significant deviations and is especially useful when making management decisions for species of conservation concern (Christopher et al. 1999). However, baseline hematology, bio- chemical, and body condition data from healthy, wild individuals are rare or nonex- istent in many wildlife species. The timber rattlesnake (Crotalus horri- dus) is the most widespread rattlesnake in the eastern US (Conant and Collins 1998), and it is imperiled at some level across much of its range (MacGowan et al. 2009); however, no baseline hematologic and plasma biochemical temporal reference intervals exist for this species. To aid in its conservation, we report baseline and tem- poral hematologic and plasma biochemical reference intervals for this species. We repeatedly captured and sampled 13 (five male and eight female) healthy, radiomarked (MacGowan and Walker 2013), free-ranging timber rattlesnakes over the course of an active season (April-September 2012) in south-central Indiana. All individuals had survived at least one winter after transmitters were implanted, indicating they had recovered. We sampled each individual between 6:00 AM and 8:00 PM at each of three sampling periods: spring (6-18 April), midsummer (9-25 July), and autumn (7-23 Septem- ber). We captured and restrained snakes using snake hooks and a snake tube. To minimize effects of handling stress on our results, we collected blood samples imme- diately upon capture (Kimble and Wil- liams 2012). We drew 0.5-1.0 mL of blood from the caudal vein using a lithium- heparinized 25-gauge, 1.9-cm needle. Immediately after blood collection, we made three blood smears per individual (Sykes and Klaphake 2008) and fixed them with 100% methanol in the field. We stored the remaining blood in lithium- heparinized tubes on ice for later labora- tory analysis. We released snakes imme- diately at the point of capture. Animals were handled according to Purdue Uni- versity Animal Care and Use Protocol 07-037.