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An early detection of parturition is generally desired to allow optimal preparation and close monitoring of the bitch in order to reduce the risk of overlooking signs of dystocia. Two studies were conducted to investigate and examine the parameter of a temperature decline in bitches before whelping and its diagnostic potential to predict parturition. In the first study a new method of body temperature measurement was applied which enables continuous sampling of vaginal temperature in bitches. A validation procedure was performed by an in vitro and in vivo experiment.
The in vitro experiment consisted of utilizing a water bath to compare values measured by the temperature loggers with those measured by a calibrated liquid-in-glass thermometer as a gold standard. The loggers (n = 26) were programmed to measure temperature in 10 second intervals. Every 10 minutes the temperature of the water bath was increased by 1 °C covering a range from 30.0 to 45.0 °C. The mean difference between the measured temperatures of the loggers and the gold standard was low (Mean ± SD = 0.1 ± 0.1 °C). An association existed between both methods (r = 1.0; p = 0.000).
The differences between the temperature loggers were small (CV = 0.0003).
The in vivo experiment was carried out with 5 healthy, privately owned, non-spayed bitches of different breeds. The loggers were programmed to measure temperatures in 10 minute intervals. For the application of the logger a sterile round speculum was inserted into the vagina. The logger was pushed through the speculum and placed approximately 18 cm deep into the vagina. This procedure as well as the logger retrievement after a three day period by means of endoscopy was well tolerated. No alterations were performed towards the bitches individual daily exercise routine or their surroundings.
Rectal temperature measurements were documented with a digital thermometer by the owners of the dogs and compared to the vaginal temperature value obtained by the logger at the same minute. The vaginal and rectal temperature were correlated (r = 0.79, p < 0.05).
The mean difference was 0.0 ± 0.2 °C (p = 0.07). 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. The macroscopic visual inspection of the vagina presented no signs of inflammation after retrievement of the logger. Overall, the results of this study indicate that the data obtained in vitro and in vivo demonstrated that this technique is a useful and accurate noninvasive method for prolonged monitoring of body temperature in bitches. Following the validation procedure of the first study the second study was conducted with 18 pregnant bitches of different breeds. The objective of this study was to record and document continuous vaginal temperature measurement and to determine sensitivity and specificity of a temperature decline to predict parturition in bitches.
Sensitivity was defined as the proportion of positive events (occurrence of delivery within 24 h, 36 h and 48 h) correctly predicted by the test (decrease of vaginal temperature). Specificity was defined as the proportion of negative events (absence of delivery within 24 h, 36 h or 48 h) correctly diagnosed as negative by the test (no decrease of vaginal temperature). Furthermore, different scenarios of measuring only once or twice daily were calculated for sensitivity and specificity for the prediction of parturition. The logger was applied into the vagina of each of the bitches on day 56 – 61 after estimated ovulation or first mating date. This procedure was performed in the dog’s familiar environment with no restrictions to their daily exercise routine.
The logger was spontaneously expelled from the vagina before delivery of the first pup. This event was defined as the time of onset of parturition. In the last 24 h before parturition mean temperature was lower (37.3 ± 0.3 °C) than 24 to 48 h (37.6 ± 0.2 °C), 49 to 72 h (37.7 ± 0.1 °C), 73 to 96 h (37.7 ± 0.1 °C) and 97 to 120 h (37.8 ± 0.1 °C, P < 0.05) earlier. Although bitches may display a decrease in vaginal temperature around the time of parturition, detecting this decrease does not determine the onset of whelping precisely. Overall the calculated values for specificity were higher than for sensitivity indicating that the prognosis of parturition not occurring is more reliable.
In conclusion veterinarians and breeders should be advised that measuring temperature around the time of parturition may assist in providing additional information regarding the onset of parturition but should be conscious of the fact that the temperature decrease may only 0.3 °C or does not occur at all. When measuring once daily at specific times the values for sensitivity were lower in the times from 2.00 – 19.00 (33.3 - 69.2 %) in comparison to measurements taken within the time range of evening and night (20.00 – 1.00, 69.2 – 84.6 %). From 2.00 – 19.00 the specificity ranged from 66.7 – 95.7% and from 20.00 – 1.00 ranged it from 88.0 – 95.8%. When monitoring temperature for the prediction of parturition it is recommendable to conduct the measurements in the later evening hours.