Climatic energy demand of horses

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Summary

The objective of this study was to determine the climatic energy demand i.e. the non-evaporative heat loss expressed in watts per square metre (W/m2) of horses at low temperatures. Five horses were used; 4 Standardbred trotters and 1 Shetland pony stallion. The horses were fed for maintenance and light work and housed in a warm environment (15–20°C). Measurements were made in a climate chamber at 6 different temperatures; -3, 6, 15, 20, 30 and 37°C. Each horse was in the climate chamber for 1.5 h on each occasion. The measuring period was 1 h. A hygrometric tent inside the climate chamber was used to measure evaporative heat loss. Ambient air temperature, radiant temperature, deep body temperature, skin and coat temperatures were measured and, together with cutaneous evaporative heat loss, used to calculate the non-evaporative heat loss. The lower critical temperature (LCT) was estimated for each horse in the study. The average LCT of horses acclimatised to an indoor temperature of 15–29°C was 18.2°C. At LCT the average total heat loss was 127 W/m2. The corresponding partitioned heat loss was 96 W/m2 non-evaporative and 31 W/m2 evaporative. The results show an average maximal tissue thermal resistance of 0.076 K·m2/W and an average thermal resistance of the coat of 0.087 K·m2/W. The climatic energy demand for these horses was 3 W/m2·°C for temperatures below LCT in dry and calm conditions. For a 500 kg horse this additional energy requirement could be met by an extra 0.15 kg hay/°C below LCT. Smaller and lighter weight horses need relatively more feed in cold conditions.

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