Body temperature of dry cows on pasture: environmental and behavioral effects.

To investigate interrelations among factors potentially affecting body temperature, we observed body temperature, activity, and relative aggregation of 3 to 5 dry cows from a herd of 12 to 15 every 20 min. Ambient conditions were noted every 1 h and fly counts every 3 h. Observations during daylight for 5 d with and without shade indicated effects of shade were minimal and were extended to 24 h without shade at six weekly intervals. Cows lie down during the evening, grazed near sunrise and sunset, and alternated standing and grazing during the day. The aggregation index was greatest during periods of standing and least during grazing; however, it remained constant across periods of similar activity. Cows shifted activity from grazing to standing during periods of increased fly activity. Ambient temperatures ranging from 13 to 35 degrees C had little influence on measured variables. Body temperatures showed one to three daily dips (greater than 1 degree C) and a hysteresis pattern. Almost all dips were associated with transitions from lying to grazing. Body temperature was constant in the morning, rose to a higher level in the afternoon, and remained high until the next morning.