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

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 (R² = 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.