Impact of climate on thermal rhythm in pastoral sheep

Tim E. Lowe, Christian J. Cook, John R. Ingram, Phillip J. Harris

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)


The effects of environmental conditions on temperature rhythms were investigated in ewe lambs at pasture. Two groups of 20 lambs had heart rate (HR), vaginal temperature (Tv), ear-canal temperature (Tc) and ear-pinna temperature (Tp) monitored continuously for 3 days. Climatic conditions were recorded at the same time and Temperature Humidity Index (THI) calculated. One group experienced fine clear weather for the 3 days, the other group experienced 2 days of heavy rain. During periods of fine weather, the daily rhythm for Tv and Tc was monophasic. However, heavy rain and a constant THI reduced the amplitude of the recorded temperature rhythms. Daily Tv and Tc patterns correlated strongly with THI, with a phase lag of 2 h. Peak Tv and Tc were at approximately 17:00 h each day. Mean maximum daily amplitudes were approximately 1.3°C for Tv and Tc. Mean Tv was 39.3±0.1 and 39.6±0.1 for weeks 1 and 2, respectively, while mean Tc was 38.9±0.1 and 39.2±0.1. Changes in Tv and Tc were closely correlated. We conclude that climate has a major effect on body temperature rhythms.

Original languageEnglish
Pages (from-to)659-664
Number of pages6
JournalPhysiology and Behavior
Issue number4-5
Publication statusPublished - 2001
Externally publishedYes


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