Relationship between Rectal Temperature and Vaginal Temperature in Grazing Bos taurus Heifers

SIMPLE SUMMARY: Body temperature is widely used to evaluate health status and thermal balance in cattle. There are numerous well-documented measures of body temperature in cattle including rectal, vaginal, tympanic, and rumen. However, in many instances, the relationship that exists between these measures has not been extensively evaluated. This study evaluated the relationship between rectal temperature and vaginal temperature in grazing beef heifers. Gaining a greater understanding of the relationships that exists between measures of body temperature may allow for greater between-study comparisons to occur. ABSTRACT: This study evaluated the relationship between rectal temperature (T(REC), °C) and vaginal temperature (T(VAG), °C) in grazing Bos taurus heifers, to develop an understanding of the reliability of these measures as estimates of core body temperature. Nineteen Angus heifers (BW = 232.2 ± 6.91 kg) were implanted with intra-rectal and intra-vaginal data loggers. Rectal temperature and T(VAG) were simultaneously recorded at 20 s intervals over 18.5 h. Heifers were housed as a singular cohort on grazing pastures for the duration of the study. A strong linear relationship (R(2) = 0.72, p < 0.0001) between the measurement sites was identified. The mean difference between T(REC) and T(VAG) was small, in which T(VAG) was on average 0.22 ± 0.01 °C lower than T(REC). Individual twenty second T(REC) and T(VAG) data were used to determine the pooled mean T(REC) and T(VAG) and then to highlight the within measure variation over time. The coefficient of variation was, on average, lower (p < 0.001) for T(VAG) (0.38%) than T(REC) (0.44%), indicating that T(VAG) exhibited less variation. Overall, the results from the current study suggest that a strong relationship exists between T(REC) and T(VAG,) and that T(VAG) may be a more reliable estimate of core body temperature than T(REC) in grazing Bos taurus heifers.