Season and physiological status affects the circadian body temperature rhythm of dairy cows

The circadian body (vaginal) temperature rhythm was measured in 36 dairy cows: Holstein-Friesian (HF. n = 12), Jersey (J, n = 12) and their crossbreed, Holstein-Friesian x Jersey (HF x J, n = 12) at six different periods (5-7 days in duration) during the year that could potentially be a seasonal and physiological stressor. These were a) early winter (late pregnancy). (b) early spring (early lactation), (c) late spring (before mating at mid-lactation). (d) early summer (after mating at mid-lactation), (e) late summer (late lactation, early pregnancy) and, (f) early autumn (drying-off at the end of lactation, mid-pregnancy). Live weight and body condition score was recorded on the first day of each measurement period. Live weight differed (P<0.001) with breed with HF cows heaviest and J cows lightest (HF: 525 +/- 51, HF x J: 456 +/- 56. J: 401 +/- 30 kg). HF cows tended (P = 0.099) to have a higher body condition than either J or HF x J cows although the overall change in body condition during the experiment was similar (P = 0.961) amongst breeds. The circadian body temperature rhythm differed markedly between each measurement period, being flatter and having a less prominent morning nadir and afternoon peak during early winter compared to spring and summer. The timing of peak body temperature was 4-5 h earlier in early autumn in HF and HF x J cows relative to J cows. There was no breed difference (P >= 0.162) in daily mean body temperature except for a tendency (P=0.075) for mean body temperature to be moderately higher in J cows (38.5 degrees C during late summer compared to HF and HF x J cows (38.4 degrees C), primarily due to an increase (P= 0.001) in daily minimum body temperature (38.0 vs. 37.8 degrees C. The daily range of oscillation (maximum-minimum) in the body temperature rhythm was highest during late summer, particularly in HF and HF x J cows. Minimum body temperature was also higher (P = 0.033) for J cows than HF and HF x J cows during early autumn (37.9 vs. 37.8 degrees C). In conclusion, season and physiological status of cattle had a profound effect on the circadian body temperature rhythm but there was little difference between the breeds of dairy cows studied. (C) 2009 Elsevier B.V. All rights reserved.