Author's address (for correspondence): Wolfgang Heuwieser, Faculty of Veterinary Medicine, Clinic for Animal Reproduction, Freie Universität, Königsweg 65, 14163 Berlin, Germany. E-mail: email@example.com
Finding innovative, non-invasive methods for continuously measuring body temperature minimizing human interference is important for accurate data collection. The objective of this study was to assess feasibility and accuracy of continuous body temperature measurements with loggers placed in the vaginal cavity of bitches. First, an in vitro experiment was performed to compare values obtained by temperature loggers (n = 26) to a calibrated liquid-in-glass thermometer. The mean differences between the two methods were low. Next, an in vivo experiment was performed using five healthy bitches, and values obtained by the vaginal loggers were compared to measurements collected rectally with digital thermometers. The results show that rectal and vaginal temperatures were correlated. The mean differences between rectal and vaginal temperatures were negligible. We conclude that the utilized temperature loggers provide accurate and reliable data.
Measurement of body temperature is considered a fundamental element of physical examination in veterinary science (Goodwin 1998), and research on minimal invasive methods is required (Greer et al. 2007; Quimby et al. 2009). Numerous technologies have been used to measure body temperature in mammals, such as subcutaneously implanted microchip transponders (Greer et al. 2007), sensors implanted into the abdomen (Refinetti and Piccione, 2005; Miyazaki et al. 2002) and ingestible temperature sensors (Angle and Gillette 2011). Another method of temperature measurement in cows utilized temperature loggers inserted into the vagina (Burdick et al. 2011; Burfeind et al. 2011). The objective of this study was to validate the application of temperature loggers (electronic devices which record and store data over time to continuously measure vaginal temperature) in bitches and to compare values obtained with rectal temperatures.
Material and Methods
Temperature measurements obtained by the loggers in vitro were compared to a calibrated liquid-in-glass thermometer, which was defined as the gold standard. Twenty-six temperature loggers (DST micro-T®, Star Oddi, Gardabaer, Iceland) were used. The temperature loggers weighed 3.3 g and had a diameter of 8.3 mm and a length of 25.4 mm. The housing material consisted of implantable, biocompatible ceramic material. The temperature loggers were programmed to measure changes in temperature at 10 s intervals. According to the manufacturer, the temperature loggers are capable of recording temperatures from 5.0°C to +45.0°C, with an accuracy of ±0.2°C and a resolution of 0.032°C. The liquid-in-glass thermometer was validated by the Office of Legal Metrology of the State of Hessen, Germany (Type E 0.1/0/50 DIN 12775; verification certificate 5-3636-09).
The devices were placed into the same water bath (F10 – UC, Julabo, Seelbach, Germany). Every 10, min the temperature of the water bath was increased by 1.0°C covering a range from 30.0 to 45.0°C. The values measured were compared to the value of the gold standard in 1-min intervals. Values measured in the 60 s following each temperature adjustment were discarded from analyses to exclude errors due to acclimatization of temperature changes. To ensure precise matching of paired observations (i.e. measured by loggers and liquid-in-glass thermometer), temperature values were read from the liquid-in-glass thermometer using a stopwatch. Data from the temperature loggers were downloaded (Mercury Application Software®, Star Oddi, Gardabaer, Iceland) and entered with the corresponding liquid-in-glass thermometer data into Excel spreadsheets (MS Office 2003; Microsoft Corporation, Redmond, WA, USA).
The second experiment consisted of five privately owned bitches which were non-spayed generally and gynaecologically healthy. An informed consent was obtained from the owner. The bitches were 7 months to 5 years old and represented following breeds: Boxer, English Setter, Rhodesian Ridgeback, German Shepherd Mix and Terrier Mix. The mean weight was 30.2 kg (range, 22.0–40.0 kg). Vaginal inspection was conducted via speculum (Model 63956, length 15 cm, diameter 2 cm, Storz, Tuttlingen, Germany). Vaginal cytology (Haema–Schnellfärbung, Labor + Technik, Berlin, Germany) was conducted before logger application and after logger removal.
To prevent movement and potential displacement, temperature loggers were attached to a progesterone-free modified Controlled Internal Drug Release (CIDR-blank, Pfizer, New York, NY, USA) device for ewes. A transponder (1.4 × 0.2 cm, BackHome Bio Tec-Transponder, Virbac Corporation, Fort Worth, TX, USA) was placed under the silicon lining of the CIDR-blank. Utilizing a reading device (Minimax II®, Virbac Corporation, Fort Worth, TX, USA), the presence and position of the logger could be confirmed. The temperature loggers were programmed to measure temperatures in 10-min intervals over a 3-day period. The logger was pushed through the speculum using a sterile swab and placed approximately 18 cm deep into the vagina. The dogs were kept in their familiar surroundings with no restrictions to their individual daily exercise routine.
To retrieve the logger, a vaginal endoscopy was performed under carbon dioxide insufflation with a rigid endoscope (S 301-4037, Dr Fritz, Tuttlingen, Germany) consisting of a telescope (4 mm diameter, length 30 cm, 30° angled lens) and a sheath (7 × 5 mm diameter, length 25 cm). The temperature logger attached to the CIDR-blank was pulled out of the vagina by means of flexible biopsy forceps (5 Fr., 40 cm, Storz, Tuttlingen, Germany). Temperature data were downloaded after removal. Rectal temperature measurements were recorded with a digital thermometer (VT 1831®, Microlife USA, Incl, Clearwater, FL, USA) and compared to the vaginal temperature measurements obtained by the logger at the same minute.
Data were analysed using SPSS® for Windows (Version 18.0, IBM Corporation, New York, NY, USA). In the in vitro experiment, the mean difference between the temperature loggers and the liquid-in-glass-thermometer was calculated using a paired t-test. Furthermore, Pearson correlation was determined between the values measured by the loggers and the liquid-in-glass thermometers. The same statistics were performed in the in vivo experiment comparing measures of rectal and vaginal temperature of the bitches. Since using correlation coefficients for clinical measurement comparison can be inappropriate, agreement between the liquid-in-glass thermometer and the logger and vaginal and rectal temperatures, respectively, were analysed graphically for both experiments using the method of Bland and Altman (1986).
In the first experiment, a total of 144 paired observations from each of the 26 temperature logger (total of 3744 paired observations) were generated and used for analysis. The mean difference between the temperature loggers and the gold standard was low (Mean ± SD = 0.1 ± 0.1°C). An association existed between both measurements (r = 1.0; p = 0.000). The differences between the 26 loggers were small (CV = 0.0003). According to Bland and Altman, mean difference was - 0.08, 95% CI:−0.02 to 0.05 (Fig. 1).
In the second experiment, a total of 118 paired observations (23.60 ± 11.37 per bitch) were used for analysis. The vaginal and rectal temperatures were correlated (r = 0.79, p< 0.05). The mean difference was 0.0 ± 0.2°C (p = 0.07). According to Bland and Altman, mean difference was 0.03, 95% CI, −0.31 to 0.37 (Fig. 2). The visual inspection of the vagina after removal of the logger did not show any macroscopic signs of inflammation. The percentages of neutrophil granulocytes in stained vaginal smear obtained immediately before logger application and after removal were 3% and 19%, 50% and 73%, 11% and 73%, 0% and 96%, and 0% and 61%, respectively.
Exploring new, non-invasive methods for measuring body temperature in animals could provide easy and reliable techniques with minimal human interference (Angle and Gillette 2011; Sousa et al. 2011). This feasibility study presents precise agreement with the gold standard in the water bath and rectal measurements. Data collection in vivo demonstrated a close correlation to rectal temperature measurements. The application and removal of the temperature logger was well tolerated with no observation of vocalization or evasive body movements. An increase of neutrophil granulocytes was found in vaginal cytology after removal of the logger. This is in accordance to the findings of Ahmadi et al. (2007) who observed changes in percentage of neutrophils after CIDR application in dairy cows. However, the visual inspection of the vagina showed no macroscopic signs of tissue irritation. The effects of this technique on tissue level in bitches should be further investigated.
The data obtained in vitro and in vivo demonstrated that the temperature loggers provide accurate, safe, easy, comfortable and reliable data. The described method may be valuable for research settings. It allows continuous sampling in females, thus collecting more data and reducing stress due to less handling of the dogs which could bias measured temperatures.
The authors thank the owners of the dogs for their fantastic cooperation and time commitment. They also thank Maria Grau for her assistance in handling of the bitches.
Conflicts of interest
None of the authors have any conflicts of interest to declare.
BM participated in the design of the study and data acquisition, carried out clinical assessments and data collection, performed data analyses and drafted the manuscript. SA participated in the design of the study and helped to draft the manuscript. OB investigated the data analyses. WH participated in the design of the study and coordination, and helped to draft the manuscript.