Sampling strategy and measurement device affect vaginal temperature outcomes in lactating dairy cattle

Abstract

Body temperature (BT) is widely used to evaluate health and heat load status in cattle. Despite its importance, studies vary in how BT is measured and in the biological interpretation of the results. Costs, practicality, labor, and welfare concerns can affect how BT is measured, including frequency of measurement and the type of device used. Inaccurate BT outcomes may have implications for cattle welfare; for example, animals may only receive treatment when fever is identified. Our objectives were (1) to compare measurement of vaginal temperature (VT) using relatively small, inexpensive, and low-accuracy loggers (±0.5 to ±1°C, iButton range; Embedded Data Systems, Lawrenceburg, KY) to a high-accuracy logger (±0.1°C; StarOddi, Gardabaer, Iceland), and (2) to evaluate how different BT sampling strategies correspond to 24-h VT in lactating dairy cows. To address the first objective, VT data from 54 cows were recorded every 45 min for 12 d/ cow, on average, using 2 different types of temperature loggers (StarOddi DST centi-T and iButton DS1921H or DS1922L) attached to a shortened, hormone-free controlled internal drug release insert. Average VT obtained from both loggers were compared using mixed models and regression analyses. In addition, we tested the consistency of the low-accuracy loggers in detecting cows with elevated BT using the kappa coefficient of concordance. To address the second objective, VT data from 20 cows were recorded every min for 9 to 11 d/ cow using StarOddi loggers. Using these data, we estimated average VT using 11 sampling strategies (every 5, 10, 15, 30, 45, 60, and 120 min, 1×/d recorded in the morning or afternoon, 2×/d, or 3×/d). Estimates and observed means were compared using linear regression. Compared with StarOddi loggers, the iButtons either underestimated (H model: 38.7 vs. 38.0 ± 0.06°C) or overestimated VT (L model: 38.7 vs. 39.2 ± 0.04°C). When considering elevated or fever VT thresholds, iButtons did not correctly classify animals; kappa coefficients of concordance were ≤0.35. Measuring VT as often as every 120 min resulted in more accurate estimates compared with strategies that recorded it once to thrice per day. These results indicate that the type of device (i.e., data logger) and sampling strategies affect BT outcomes and that these decisions affect the interpretation of BT data.

Recent Advances on Early Detection of Heat Strain in Dairy Cows Using Animal-Based Indicators: A Review

“…A daily temperature circadian rhythm in cattle older than two months was observed with RT at dusk up to 1.4 • C higher than that in dawn [60]. It is noted by Tresoldi et al [36] that RT measured a few times a day may result in a relatively lower daily average, especially when measuring only once in the morning. Except for circadian rhythm, many heat-producing events (e.g., feeding, exercise, estrus) would lead to an increased RT [30,60].…”

“…The prices of data loggers vary distinctly. When considering elevated VT thresholds, inexpensive data loggers failed to correctly classify animals compared with an expensive and high-accurate data logger [36].…”

“…VT is highly correlated with RT with a correlation coefficient up to 0.97 and the measured values are very close, especially when measuring with the same temperature loggers [33,35,67,68]. This correlation is highly biased by the accuracy of the devices, as the digital thermometers used for RT measurement are supposed to have higher accuracy than most of the data loggers used for measuring VT [33,36]. Mean VT was found higher than mean RT which might be due to the fact that the data logger measuring VT was inserted into the vagina deeper than the thermometer measuring RT [34].…”

“…All the indwelling devices for measuring VT can only be placed in the vagina for up to 24 days (around a week in most applications) [31,36] due to the increased risk of irritation and infection [35]. Thus, long-term monitoring cannot be carried out and only short-term monitoring is meaningful for research purposes.…”

“…Due to the access to continuous measurement, VT is better at describing circadian rhythm than RT [33]. To reflect daily average CBT accurately, VT should be measured every 120 min or more [36].…”