Circadian and Ultradian Temperature Rhythms of Lactating Dairy Cows

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Abstract
Thermistors were implanted in the right front quarter of udder and peritoneal cavity of 6 lactating Holstein cows to investigate whether udder temperature is regulated independently of deep body temperature. Sequential measurements of udder, body chamber and outdoor temperatures were every 1.4 min (1024 readings/probe per 24 h) by digital computer. Cows were housed (except for short exercise periods) in a chamber at 16.7 .+-. 0.3.degree. C, lights on from 0730-1630 h and 2100-0200 h. Temperature was monitored continuously for 5 days in 3 cows in early lactation and in 3 cows in late lactation. Udder temperature was closely correlated with body temperature (body and udder temperatures were 38.8 .+-. 0.1.degree. C). Five of 6 cows showed 2 patterns of temperature variation: a 24-h pattern with 2 troughs each day, minimum at 0930-1100 h, increase 1.0.degree. C by 1200-1300 h, decline 1.degree. C from 2000-2200 h, 2nd minimum by 2100-2200 h, and constant elevation from 2300-0800 h (peak to trough, 1.23 .+-. 0.09.degree. C); and superimposed on the 24-h rhythm was an ultradian rhythm with an approximate 90 min period (peak to trough, 0.5 .+-. 0.03.degree. C). Rhythmicity of udder and body temperatures should be considered in research on the chronobiology of milk secretion and mastitis.