|Title||Grazing behavior of free-ranging beef cows to initial and prolonged exposure to fluctuating thermal environments|
|Publication Type||Journal Article|
|Year of Publication||1994|
|Authors||Prescott, M, Havstad, KM, Olson-Rutz, KM, Ayers, EL, Petersen, MK|
Effects of initial and prolonged exposure to cold ambient temperatures on the behaviors of free-ranging beef cows were examined over a fall and winter season. Mean daily temperature (<i>MDT</i>) and short-term thermal stress (<i>STTS</i>) were used to express thermal stressors. Short-term thermal stress was defined as the deviation of the current day's mean temperature from a running mean temperature of previous days (an acclimation period). Twenty different acclimation periods (calculated using temperatures from the previous 1–20 days) were used to express 20 different acclimation lengths for determining <i>STTS</i>. Daily grazing time and forage intake were estimated for 15, 6-year-old gestating cows during January and February (winter trial), and for 12 of these cows during October and November (fall trial). In the winter, daily grazing time increased with increased ambient temperature and decreased with increased thermal stress (<i>P</i><0.10). Observed fluctuations in winter daily grazing time in relation to thermal stress were less than 84 min day<sup>-1</sup>. Daily grazing time was lower in the fall than winter. Cattle acclimated more quickly to <i>STTS</i> in the winter than in the fall. However, forage intake was consistent during both seasons and unresponsive to thermal stress. The thermal environment in these northern latitudes appeared to be only a minor influence upon grazing behaviors. It is likely that forage quality and availability, and accessibility of sites with moderate microclimates are more important environmental features effecting daily intake and total grazing time.