This report presents data on the effect of low fluctuating ambient air temperatures on the rectal temperature, heart rate, and respiration rate in lactating Holstein-Friesian cows.Daily minimum ambient air temperature (DMAAT) inside the uninsulated University of Saskatchewan loose-housing shed ranged from −5° F. to 38° F. As ambient temperature decreased, rectal temperature and heart rate increased, while respiration rate decreased. Levels of significance were 10, 9, and 1 per cent for regressions of rectal temperature, heart rate, and respiration rate, respectively, on DMAAT. Levels of significance were 7, 10, and 1 per cent for regressions of rectal temperature, heart rate, and respiration rate, respectively, on degree hours per day (d-h/day). Degree hours per day is a measurement unit developed by the authors and is based on time and difference in degrees from 50° F.Change in rectal temperature and heart rate were not significantly (P = >.05) correlated with either change in d-h/day or change in DMAAT. Change in respiration rate was significantly (P = <.02) and negatively correlated with change in d-h/day and significantly (P = <.06) and positively correlated with change in DMAAT.Heart rate, rectal temperature, and respiration rate were not significantly correlated with each other. However, change in respiration rate was positively correlated with change in rectal temperature (P = <.03).While the influence of low temperatures resulted in small changes in these physiological characteristics compared to those experienced elsewhere in high temperature zones, it cannot be concluded that lactating cows were entirely free of thermal stress at temperatures as low as 0° F.
Effect modification of omega-3 fatty acids on short-term associations between ambient air temperature and heart rate variability
