The effects of thermoregulatory behaviour on the heat loss from shorn sheep as measured by a model ewe for micro-climate integration

A thermostatic, taxidermic model sheep was used to assess the effects of thermoregulatory behaviour of shorn sheep at night in a winter environment with mean air temperatures slightly above freezing, variable wind speeds, rain and cloud cover.Testing in a wind tunnel showed that angle of incidence to the wind had no effect on heat loss at wind speeds < 2 m s⁻¹ (7 km h⁻¹), but at wind speeds of 7 m s⁻¹ (25 km h⁻¹), heat loss was 14% greater when the model was side-on rather than tail- or head-on to the wind.In tests on pasture, standing side-on to the early morning sun reduced heat loss from the model by 33%. Three hours “lying” on the lee side of a 1-m high synthetic Sarlon windbreak on a frosty night resulted in a reduction in heat loss of 6% below that when standing or 11% below that in a standing position in the open. When the model was placed in the centre of a tight group of 16 shorn sheep, its heat loss was reduced by an average of 14%.Heat loss was also reduced if the model was moved from the open, to regions of lower wind speed adjacent to windbreaks; the effect was greater on the leeward than the windward side.The reduction one metre leeward of a grass hedge (hybrid Phalaris) was 15% compared with 12% one metre leeward of a synthetic (Sarlon) windbreak, which is consistent with the preference of shorn sheep to shelter by Phalaris rather than Sarlon windbreaks.The microclimates where heat loss from the model were lowest correspond to those sought by shorn sheep in cold weather, and the results indicate that shorn sheep have very sensitive thermosensing mechanisms and efficient thermoregulatory behaviour.